query: when does the acrosome reaction occur in sperm

pos: Acrosome reaction Acrosome reaction During fertilization, a sperm must first fuse with the plasma membrane and then penetrate the female egg in order to fertilize it. Fusing to the egg usually causes little problem, whereas penetrating through the egg's hard shell or extracellular matrix can present more of a problem to the sperm. Therefore, sperm cells go through a process known as the acrosome reaction which is the reaction that occurs in the acrosome of the sperm as it approaches the egg. The "acrosome" is a cap-like structure over the anterior half of the sperm's head. As the sperm approaches the zona

pos: Acrosome reaction Acrosome reaction During fertilization, a sperm must first fuse with the plasma membrane and then penetrate the female egg in order to fertilize it. Fusing to the egg usually causes little problem, whereas penetrating through the egg's hard shell or extracellular matrix can present more of a problem to the sperm. Therefore, sperm cells go through a process known as the acrosome reaction which is the reaction that occurs in the acrosome of the sperm as it approaches the egg. The "acrosome" is a cap-like structure over the anterior half of the sperm's head. As the sperm approaches the zona

pos: Acrosome reaction Acrosome reaction During fertilization, a sperm must first fuse with the plasma membrane and then penetrate the female egg in order to fertilize it. Fusing to the egg usually causes little problem, whereas penetrating through the egg's hard shell or extracellular matrix can present more of a problem to the sperm. Therefore, sperm cells go through a process known as the acrosome reaction which is the reaction that occurs in the acrosome of the sperm as it approaches the egg. The "acrosome" is a cap-like structure over the anterior half of the sperm's head. As the sperm approaches the zona

neg: Acrosome reaction the acrosome reaction has already occurred, sperm are then able to penetrate the zona pellucida due to mechanical action of the tail, not because of the acrosome reaction itself. The first stage is the penetration of corona radiata, by releasing hyaluronidase from the acrosome to digest cumulus cells surrounding the oocyte and exposing acrosin attached to the inner membrane of the sperm. The cumulus cells are embedded in a gel-like substance made primarily of hyaluronic acid, and developed in the ovary with the egg and support it as it grows. It is necessary for the acrosome reaction to occur before

neg: Acrosome reaction mind that a certain percentage of sperm cells will undergo a spontaneous acrosome reaction without the presence of the ovum. Those cells are not able to fertilise the egg, even if they do reach it later. Other cells will spontaneously shed their acrosome during the process of apoptosis/necrosis. When using intracytoplasmic sperm injection (ICSI) for IVF, the implantation rate is higher in oocytes injected with spermatozoa that have undergone acrosome reaction (~40%) vs. those injected with nonreacted spermatozoa (~10%). The implantation rate is ~25% in when injected with both reacted and nonreacted spermatozoa. The delivery rate per cycle follows the

neg: Acrosome reaction species a protuberance (the acrosomal process) forms at the apex of the sperm head, supported by a core of actin microfilaments. The membrane at the tip of the acrosomal process fuses with the egg's plasma membrane. In some echinoderms, including starfish and sea urchins, a major portion of the exposed acrosomal content contains a protein that temporarily holds the sperm on the egg's surface. In mammals the acrosome reaction releases hyaluronidase and acrosin; their role in fertilization is not yet clear. The acrosomal reaction does not begin until the sperm comes into contact with the oocyte's zona pellucida. Upon coming

neg: Acrosome reaction "acrosome reaction". The sperm cell acquires a "hyperactive motility pattern" by which its flagellum produces vigorous whip-like movements that propel the sperm through the cervical canal and uterine cavity, until it reaches the isthmus of the fallopian tube. The sperm approaches the ovum in the ampulla of the fallopian tube with the help of various mechanisms, including chemotaxis. Glycoproteins on the outer surface of the sperm then bind with glycoproteins on the zona pellucida of the ovum. Sperm that did not initiate the acrosome reaction prior to reaching to the zona pellucida are unable to penetrate the zona pellucida. Since

neg: Acrosome vitro" by substances a sperm cell may encounter naturally such as progesterone or follicular fluid, as well as the more commonly used calcium ionophore A23187. This can be done to serve as a positive control when assessing the acrosome reaction of a sperm sample by flow cytometry or fluorescence microscopy. This is usually done after staining with a fluoresceinated lectin such as FITC-PNA, FITC-PSA, FITC-ConA, or fluoresceinated antibody such as FITC-CD46. In the case of globozoospermia (sperm with round heads), the Golgi apparatus is not transformed into the "acrosome", causing male infertility. Acrosome The acrosome is an organelle that develops

neg: Fertilisation the sperm and activating the acrosome reaction. ZP3 is sufficient though unnecessary for sperm/egg binding. Two additional sperm receptors exist: a 250kD protein that binds to an oviduct secreted protein, and SED1, which independently binds to the zona. After the acrosome reaction, the sperm is believed to remain bound to the zona pellucida through exposed ZP2 receptors. These receptors are unknown in mice but have been identified in guinea pigs. In mammals, the binding of the spermatozoon to the GalT initiates the acrosome reaction. This process releases the hyaluronidase that digests the matrix of hyaluronic acid in the vestments around

neg: Acrosome reaction same trend. The acrosome reaction can be stimulated in vitro by substances a sperm cell may encounter naturally such as progesterone or follicular fluid, as well as the more commonly used calcium ionophore A23187. Birefringence microscopy, flow cytometry or fluorescence microscopy can be used for assessing the shedding of the acrosome or "acrosome reaction" of a sperm sample. Flow cytometry and fluorescence microscopy are usually done after staining with a fluoresceinated lectin such as FITC-PNA, FITC-PSA, FITC-ConA, or fluoresceinated antibody such as FITC-CD46. The antibodies/lectins have a high specificity for different parts of the acrosomal region, and will only bind

neg: Acrosome Acrosome The acrosome is an organelle that develops over the anterior half of the head in the spermatozoa (sperm cells) of many animals including humans. It is a cap-like structure derived from the Golgi apparatus. Acrosome formation is fully completed 5–10 years after testicular maturation. In Eutherian mammals the acrosome contains digestive enzymes (including hyaluronidase and acrosin). These enzymes break down the outer membrane of the ovum, called the zona pellucida, allowing the haploid nucleus in the sperm cell to join with the haploid nucleus in the ovum. This shedding of the acrosome, or acrosome reaction, can be stimulated "in

neg: Acrosome reaction into contact with the zona pellucida, the acrosomal enzymes begin to dissolve and the actin filament comes into contact with the zona pellucida. Once the two meet, a calcium influx occurs, causing a signaling cascade. The cortical granules inside the oocyte then fuse to the outer membrane and a transient fast block reaction occurs. It also alters a patch of pre-existing sperm plasma membrane so that it can fuse with the egg plasma membrane. A sperm penetration assay includes an acrosome reaction test that assesses how well a sperm is able to perform during the fertilization process. Sperm that are

neg: Acrosome reaction unable to properly go through the acrosome reaction will not be able to fertilize an egg. However, this problem only occurs in about 5% of men that have the test done. This test is rather expensive and provides limited information on a man's fertility. In other cases, such as in the wood mouse "Apodemus sylvaticus", premature acrosome reactions have been found to cause increased motility in aggregates of spermatozoa promoting fertilization. The acrosomal reaction normally takes place in the ampulla of the fallopian tube (site of fertilization) when the sperm penetrates the secondary oocyte. A few events precede the actual

neg: Hyperactivation Hyperactivation Hyperactivation is a type of sperm motility. Hyperactivated sperm motility is characterised by a high amplitude, asymmetrical beating pattern of the sperm tail (flagellum). This type of motility may aid in sperm penetration of the zona pellucida, which encloses the ovum. Hyperactivation could then be followed by the acrosome reaction where the cap-like structure on the head of the cell releases the enzymes it contains. This facilitates the penetration of the ovum and fertilisation. Some definitions consider sperm activation to consist of these two processes of hyperactivation and the acrosome reaction Hyperactivation is a term also used to express

neg: Acrosome reaction to a specific site (acrosomal content/ inner/outer membrane). If bound to a fluorescent molecule, regions where these probes have bound can be visualised. Sperm cells with artificially induced acrosome reactions may serve as positive controls. For fluorescence microscopy a smear of washed sperm cells are made, airdried, permealized and then stained. Such a slide is then viewed under light of a wavelength that will cause the probe to fluoresce if it is bound to the acrosomal region. At least 200 cells are viewed in an arbitrary fashion and classified as either acrosome intact (fluorescing bright green) or acrosome reacted (no

neg: Acrosome reaction pellucida of the egg, which is necessary for initiating the acrosome reaction, the membrane surrounding the acrosome fuses with the plasma membrane of the sperm's head, exposing the contents of the acrosome. The contents include surface antigens necessary for binding to the egg's cell membrane, and numerous enzymes which are responsible for breaking through the egg's tough coating and allowing fertilization to occur. There are considerable species variations in the morphology and consequences of the acrosome reaction. In several species the trigger for the acrosome reaction has been identified in a layer that surrounds the egg. In some lower animal

neg: Human fertilization undergo capacitation in the female's reproductive tract over several hours, which increases its motility and destabilizes its membrane, preparing it for the acrosome reaction, the enzymatic penetration of the egg's tough membrane, the zona pellucida, which surrounds the oocyte. After binding to the corona radiata the sperm reaches the zona pellucida, which is an extra-cellular matrix of glycoproteins. A special complementary molecule on the surface of the sperm head binds to a ZP3 glycoprotein in the zona pellucida. This binding triggers the acrosome to burst, releasing enzymes that help the sperm get through the zona pellucida. Some sperm cells consume

neg: Spermatozoon into the tails. The whip-like tail (flagellum) of the sperm is studded with ion channels formed by proteins called CatSper. These channels are selective, allowing only calcium ions to pass. The opening of CatSper channels is responsible for the influx of calcium. The sudden rise in calcium levels causes the flagellum to form deeper bends, propelling the sperm more forcefully through the viscous environment. Sperm hyperactivity is necessary for breaking through two physical barriers that protect the egg from fertilization. The second process in sperm activation is the acrosome reaction. This involves releasing the contents of the acrosome, which disperse,

neg: Biochemical cascade the ability to fertilize the female gamete, this cell suffers capacitation and acrosome reaction in female reproductive tract. The signaling pathways best described for spermatozoon involve these processes. The cAMP/PKA signaling pathway leads to sperm cells capacitation; however, adenilyl cyclase in sperm cells is different from the somatic cells. Adenilyl cyclase in spermatozoon doesn't recognize G proteins, so it is stimulated by bicarbonate and Ca ions. Then, it converts ATP into cAMP, which activates PKA. PKA leads to protein tyrosine phosphorylation. Phospholipase C (PLC) is involved in acrosome reaction. ZP3 is a glycoprotein present in zona pelucida and it interacts

neg: Acrosome reaction from binding. There is some evidence that this binding is what triggers the acrosome to release the enzymes that allow the sperm to fuse with the egg. It is likely that a similar mechanism occurs in other mammals, but the diversity of zona proteins across species means that the relevant protein and receptor may differ. More recent scientific evidence demonstrate the acrosomal reaction is necessary to expose a protein called IZUMO1 on the sperm, however, it is not critical for penetration of the egg shell or zona pellucida. As seen in mouse studies, IZUMO1 binds to the oocyte protein JUNO

neg: Acrosome reaction probe present, or only on the equatorial region). It is then expressed as a percentage of the counted cells. For assessment with flow cytometry the washed cells are incubated with the chosen probe, (possibly washed again) and then sampled in a flow cytometer. After gating the cell population according to forward- and side-scatter the resulting data can be analysed (E.g. mean fluorescences compared). With this technique a probe for viability, like propidium iodide (PI) could also be included in order to exclude dead cells from the acrosome assessment, since many sperm cells will spontaneously lose their acrosome when they die.

neg: Human fertilization be expelled by exocytosis to the zona pellucida. This in turn causes the glyco-proteins in the zona pellucida to cross-link with each other — i.e. the enzymes cause the ZP2 to hydrolyse into ZP2f — making the whole matrix hard and impermeable to sperm. This prevents fertilization of an egg by more than one sperm. The cortical reaction and acrosome reaction are both essential to ensure that only one sperm will fertilize an egg. After the sperm enters the cytoplasm of the oocyte (also called ovocyte), the tail and the outer coating of the sperm disintegrate and the cortical reaction

neg: Human embryogenesis directs the movement of the sperm towards the ovum. Secondly there is an adhesive compatibility between the sperm and the egg. With the sperm adhered to the ovum, the third process of acrosomal reaction takes place; the front part of the spermatozoan head is capped by an acrosome which contains digestive enzymes to break down the zona pellucida and allow its entry. The entry of the sperm causes calcium to be released which blocks entry to other sperm cells. A parallel reaction takes place in the ovum called the zona reaction. This sees the release of cortical granules that release

neg: Hamster zona-free ovum test However, the incidence of acrosome reaction in freely swimming human sperm does not accurately reflect the fertilizing ability of the sperm. The practice is made licensable in the United Kingdom by the Human Fertilisation and Embryology Act 1990. This test has a poor predictive value for the success of fertilization in IVF treatment at any insemination concentration. No strong correlation has been found between hamster egg penetration rates and the various semen parameters and the role of the hamster egg penetration test in the investigation of the causes of infertility should be evaluated further. However, a negative result on the

neg: Capacitation not require this capacitation step and are ready to fertilize an oocyte immediately after release from the male. After this capacitation, the sperm must undergo the final maturation step, activation, involving the acrosome reaction. Historically, the term "capacitation" has evolved in meaning and this should be taken into account when consulting sources. Capacitation has 2 effects: destabilisation of the acrosomal sperm head membrane which allows it to penetrate the outer layer of the egg, and chemical changes in the tail that allow a greater mobility in the sperm. The changes are facilitated by the removal of sterols (e.g. cholesterol) and

neg: Acrosin the zymogen form of the protease is then processed into its active form, β-acrosin. The active enzyme then functions in the lysis of the zona pellucida, thus facilitating penetration of the sperm through the innermost glycoprotein layers of the ovum. The importance of acrosin in the acrosome reaction has been contested. It has been found through genetic knockout experiments that mouse spermatozoa lacking β-acrosin (the active protease) still have the ability to penetrate the zona pellucida. Thus, some argue for its role in assisting in the dispersal of acrosomal contents following the acrosome reaction, while others demonstrate evidence for its

neg: Cortical reaction the acrosomal reaction within the sperm, where the acrosome, a specialized secretory vesicle that is homologous to cortical granules, is fused with the plasma membrane of the sperm cell to release its contents which degrade the egg's tough coating and allow the sperm to bind to and fuse with the egg. In the well-studied sea urchin model system, the granule contents modify a protein coat on the outside of the plasma membrane (the vitelline layer) so that it is released from the membrane. The released cortical granule proteins exert a colloid osmotic pressure causing water to enter the space between

neg: Hyperactivation epithelium. Thus, only those sperm which have undergone hyperactivation have the ability to fertilize the egg. Hyperactivation Hyperactivation is a type of sperm motility. Hyperactivated sperm motility is characterised by a high amplitude, asymmetrical beating pattern of the sperm tail (flagellum). This type of motility may aid in sperm penetration of the zona pellucida, which encloses the ovum. Hyperactivation could then be followed by the acrosome reaction where the cap-like structure on the head of the cell releases the enzymes it contains. This facilitates the penetration of the ovum and fertilisation. Some definitions consider sperm activation to consist of these

neg: Acrosome reaction and once bound together, the sperm and the egg fuse together to form two pronuclei These pronuclei supply the zygote with the genetic material necessary for the formation of an embryo. Additionally, once the fusion of the sperm and oocyte is complete, phospholipase C zeta is released from the sperm. As the sperm arrive at the egg, it is the egg that chooses the sperm and pulls it towards her. The selected sperm actually tries to swim away from the egg but is tethered to the egg by female hormones. The membrane around the egg literally opens up and swallows

neg: Intracytoplasmic sperm injection Intracytoplasmic sperm injection Intracytoplasmic sperm injection (ICSI ) is an in vitro fertilization (IVF) procedure in which a single sperm cell is injected directly into the cytoplasm of an egg. This technique is used in order to prepare the gametes for the obtention of embryos that may be transferred to a maternal uterus. With this method acrosome reaction is skipped. There are several differences within classic IVF and ICSI. However, the steps to be followed before and after insemination are the same. In terms of insemination, ICSI needs one only sperm cell per oocyte, meanwhile IVF needs between 50 and

neg: Hamster zona-free ovum test whose sperm fail the hamster test are a third as fertile than those whose sperm pass. Donated sperm and intracytoplasmic sperm injection techniques are considered more strongly for those whose sperm fail this test. Contrary to some assertions by medical professionals, if the human sperm penetrates the hamster egg, a hybrid embryo is indeed created. The resulting hamster-hybrid is known as a humster. These embryos are typically destroyed before they divide into two cells and are never known to have been implanted in either a hamster or human uterus to develop. This test evaluates the acrosome reaction of human spermatozoa.

neg: Intracytoplasmic sperm injection twin pregnancies with a second gestational sac with a dead fetus, first trimester screening should be based solely on the maternal age and the nuchal translucency scan as biomarkers are significantly altered in these cases. Intracytoplasmic sperm injection Intracytoplasmic sperm injection (ICSI ) is an in vitro fertilization (IVF) procedure in which a single sperm cell is injected directly into the cytoplasm of an egg. This technique is used in order to prepare the gametes for the obtention of embryos that may be transferred to a maternal uterus. With this method acrosome reaction is skipped. There are several differences within

neg: Veratridine applicability as a neuropharmacological tool for the study of electrical properties of nerve and muscle fibers. It has also been tested as a treatment for myasthenia gravis, in light of its potential to increase muscle responses to motor neuron stimulation. Furthermore, this compound has recently been reported to increase sperm progressive motility (although it does not produce hyperactivation by itself). It has the potential of enhancing protein tyrosine phosphorylation, which takes place during capacitation, and its eﬀects are inhibited in the presence of lidocaine and tetrodotoxin. Veratridine has not been reported to have any eﬀect on the acrosome reaction on

neg: Acrosome reaction the sperm cell reaches the zona pellucida. Acrosin digests the zona pellucida and membrane of the oocyte. Part of the sperm's cell membrane then fuses with the egg cell's membrane, and the contents of the head sink into the egg. In the mouse it has been demonstrated that ZP3, one of the proteins that make up the zona pellucida, binds to a partner molecule (to the β1,4-galactosyl transferase receptors) on the sperm. This lock-and-key type mechanism is species-specific and prevents the sperm and egg of different species from fusing. The zona pellucida also releases Ca granules to prevent additional sperm

neg: Antisperm antibodies or anal intercourse. In both men and women, ASA production are directed against surface antigens on sperm, which can interfere with sperm motility and transport through the female reproductive tract, inhibiting capacitation and acrosome reaction, impaired fertilization, influence on the implantation process, and impaired growth and development of the embryo. As of 2017 research was ongoing in several areas related to ASA. Research has been conducted, but not clinically tested, to use sperm antigens or recombinant ASAs as contraceptive vaccines for humans, as well as captive and wild animals. The mechanisms through which both women and men develop ASA is

neg: Human fertilization their acrosome prematurely on the surface of the egg cell, facilitating the penetration by other sperm cells. As a population, sperm cells have on average 50% genome similarity so the premature acrosomal reactions aid fertilization by a member of the same cohort. It may be regarded as a mechanism of kin selection. Recent studies have shown that the egg is not passive during this process. Once the sperm cells find their way past the zona pellucida, the cortical reaction occurs. Cortical granules inside the secondary oocyte fuse with the plasma membrane of the cell, causing enzymes inside these granules to

neg: Acroplaxome Acroplaxome Spermatozoa develop in the seminiferous tubules of the testes. During their development the spermatogonia proceed through meiosis to become spermatozoa. Many changes occur during this process: the DNA in nuclei becomes condensed; the acrosome develops as a structure close to the nucleus. The acrosome is derived from the Golgi apparatus and contains hydrolytic enzymes important for fusion of the spermatozoon with an egg cell. During spermiogenesis the nucleus condenses and changes shape. Abnormal shape change is a feature of sperm in male infertility. The acroplaxome is a structure found between the acrosomal membrane and the nuclear membrane. The acroplaxome

neg: Acroplaxome contains structural proteins including keratin 5, F-actin and profilin IV. Acroplaxome Spermatozoa develop in the seminiferous tubules of the testes. During their development the spermatogonia proceed through meiosis to become spermatozoa. Many changes occur during this process: the DNA in nuclei becomes condensed; the acrosome develops as a structure close to the nucleus. The acrosome is derived from the Golgi apparatus and contains hydrolytic enzymes important for fusion of the spermatozoon with an egg cell. During spermiogenesis the nucleus condenses and changes shape. Abnormal shape change is a feature of sperm in male infertility. The acroplaxome is a structure found

neg: Veratridine its own, but it is able to block the progesterone-induced acrosome reaction. Moreover, veratridine has the effect of turning the membrane potential to a more positive one and also modiﬁes the eﬀect of progesterone on [Ca2+]i and sperm membrane potential. The activation of Nav1.8 is a key point in Veratradine's mechanism of action and, consequently, this sodium ion channel coordinates the effects of this compound. Veratradine also activates additional Nav channels. These facts contribute to support the importance of these Veratradine-sensitive proteins in the regulation of mature sperm function, such as human sperm fertility acquisition regulating motility, capacitation and the

neg: VEZT to the fusion of the sperm with the egg as, it is the outer acrosomal domain which initiates the acrosome reaction, enabling the sperm to fuse. Vezatin is present in both these domains, but the translocation of vezatin from the inner to the outer membrane is unknown. Furthermore, vezatin is not expressed in the epididymal cells, thus vezatin cannot be added to the exterior membrane during maturation of the spermatozoa. However, knowledge of the localisation of vezatin in this outer membrane and its known role in adherens junctions suggests that it plays a role in the fusion of the mammalian

neg: Zona pellucida system), the zona glycoprotein, ZP3, is responsible for sperm binding, adhering to proteins on the sperm plasma membrane (GalT). ZP3 is then involved in the induction of the acrosome reaction, whereby a spermatozoon releases the contents of the acrosomal vesicle. The exact characterisation of what occurs in other species has become more complicated as further zona proteins have been identified. In humans, five days after the fertilization, the blastocyst performs zona hatching; the zona pellucida degenerates and decomposes, to be replaced by the underlying layer of trophoblastic cells. The zona pellucida is essential for oocyte growth and fertilization. In some

neg: Intracytoplasmic sperm injection 100 thousands. This is due to the fact that in IVF acrosome reaction has to take place and thousands of sperm cells have to be involved. Once fertilized, the egg is transformed into a proembryo and it has to be transferred to the uterus to continue its development. The first human pregnancy generated by ICS was carried out in 1991 by Gianpiero Palermo and his team. Round spermatid injection (ROSI) is a technique of assisted reproduction whereby a round spermatid is injected into oocyte cytoplasm in order to achieve fertilization. This technique can be used to enable genetic fatherhood to

neg: Reproductive immunology and hopefully will be an effective contraceptive for humans. Normally, spermatozoa fuse with the zona pellucida surrounding the mature oocyte; the resulting acrosome reaction breaks down the egg's tough coating so that the sperm can fertilize the oovum. The mechanism of the vaccine is injection with cloned ZP cDNA, therefore this vaccine is a DNA based vaccine. This results in the production of antibodies against the ZP, which stop the sperm from binding to the zona pellucida and ultimately from fertilizing the oovum. Another vaccine in investigation is one against HCG. This immunization would produce antibodies against hCG and TT.

neg: Acrosome reaction the sperm. Upon penetration, if all is occurring normally, the process of egg-activation occurs and the oocyte is said to have become activated. This is thought to be induced by a specific protein phospholipase c zeta. It undergoes its secondary meiotic division, and the two haploid nuclei (paternal and maternal) fuse to form a zygote. In order to prevent polyspermy and minimise the possibility of producing a triploid zygote, several changes to the egg's cell membranes renders them impenetrable shortly after the first sperm enters the egg. The aforementioned process describes the physiologically relevant events. One should however bear in

neg: Testicular immunology "Chlamydia trachomatis" which infects the genitals. It more commonly affects women, and if untreated, can lead to pelvic inflammatory disease and infertility. Serious symptoms in men are rare, but include swollen testicles and an unusual discharge from the penis. It is effectively treated with antibiotics. Antisperm antibodies (ASA) have been considered as infertility cause in around 10–30% of infertile couples. ASA production are directed against surface antigens on sperm, which can interfere with sperm motility and transport through the female reproductive tract, inhibiting capacitation and acrosome reaction, impaired fertilization, influence on the implantation process, and impaired growth and development of

neg: Biochemical cascade dispersion of actin and consequently promotes plasmatic membrane and outer acrosome membrane fusion. Progesterone is a steroid hormone produced in cumulus oophorus. In somatic cells it binds to receptors in nucleus; however, in spermatozoon its receptors are present in plasmatic membrane. This hormone activates AKT that leads to activation of other protein kinases, involved in capacitation and acrosome reaction. When ROS (reactive oxygen species) are present in high concentration, they can affect the physiology of cells, but when they are present in moderated concentration they are important for acrosome reaction and capacitation. ROS can interact with cAMP/PKA and progesterone pathway,

neg: Corona radiata (embryology) primary stage. These cuboidal granulosa cells, also known as the granulosa radiata, form more layers throughout the maturation process, and remain attached to the zona pellucida after the ovulation of the Graafian follicle. For fertilization to occur, sperm cells rely on hyaluronidase (an enzyme found in the acrosome of spermatozoa) to disperse the corona radiata from the zona pellucida of the secondary (ovulated) oocyte, thus permitting entry into the perivitelline space and allowing contact between the sperm cell and the nucleus of the oocyte. Corona radiata (embryology) The corona radiata is the innermost layer of the cells of the cumulus

neg: Asthenozoospermia which allows the fluidy of the membrane, necessary to the fusion with the ovule. Studies in mice have shown that DHA is essential for acrosome reaction and a DHA deficiency results in abnormal sperm morphology, lost of motility and infertility; which can be restored by dietary DHA supplementation. Futhermore, the supplementation with DHA in human has been reported to increase sperm motility. But also, DHA supplement can protect spermatozoa against the damage caused by the cryopresevation process. González-Ravina, Cristina; Aguirre-Lipperheide, Mercedes; Pinto, Francisco; Martín-Lozano, David; Fernández-Sánchez, Manuel; Blasco, Víctor; Santamaría-López, Esther; Candenas, Luz (2018). "Effect of dietary supplementation with a

neg: Female infertility menopausal levels after four series. Other hormonal changes in chemotherapy include decrease in inhibin B and anti-Müllerian hormone levels. Women may choose between several methods of fertility preservation prior to chemotherapy, including cryopreservation of ovarian tissue, oocytes or embryos. Antisperm antibodies (ASA) have been considered as infertility cause in around 10–30% of infertile couples. ASA production are directed against surface antigens on sperm, which can interfere with sperm motility and transport through the female reproductive tract, inhibiting capacitation and acrosome reaction, impaired fertilization, influence on the implantation process, and impaired growth and development of the embryo. Factors contributing to the

neg: Human fertilization Upon encountering the secondary oocyte, the acrosome of the sperm produces enzymes which allow it to burrow through the outer jelly coat of the egg. The sperm plasma, then fuses with the egg's plasma membrane, the sperm head disconnects from its flagellum and the egg travels down the Fallopian tube to reach the uterus. In vitro fertilization (IVF) is a process by which egg cells are fertilized by sperm outside the womb, "in vitro". The sperm binds through the corona radiata, a layer of follicle cells on the outside of the secondary oocyte. Fertilization occurs when the nucleus of both

neg: VEZT almost always expressed with vezatin but the absence of this partnership within the testis is yet to be fully understood. However, vezatin has been shown to be expressed within the acrosomal region of the actual spermatozoa. Vezatin is not found in the early spermatid but only appears when the formation of the acrosome occurs later on in the process of spermatogenesis. The acrosome itself is divided into two functional domains, the inner acrosomal membrane which faces the nucleus and the outer acrosomal membrane which is in contact with the exterior surfaces of the sperm. This compartmentalisation of functions is vital

neg: ADCY10 ADCY10 Adenylyl cyclase 10 also known as ADCY10 is an enzyme that, in humans, is encoded by the "ADCY10" gene. The protein encoded by this gene belongs to a distinct class of mammalian adenylyl cyclase that is soluble and insensitive to G protein or forskolin regulation. It is localized in the cytoplasm and is thought to function as a general bicarbonate sensor throughout the body. It may also play an important role in the generation of cAMP in spermatozoa, implying possible roles in sperm maturation through the epididymis, capacitation, hypermotility, and/or the acrosome reaction. Mutations in the "ADCY10" gene are

neg: Zona pellucida injected into the bloodstream of another, it results in sterility of the second species due to immune response. This effect can be temporary or permanent, depending on the method used. In New Jersey, immunocontraception using porcine zona pellucida has been trialled for the control of deer populations, for example using the products "SpayVac" and "GonaCon". There are four major "zona pellucida glycoproteins", termed ZP1-4. ZP1, ZP3 and ZP4 bind to capacitated spermatozoa and induce the acrosome reaction. Successful fertilization depends on the ability of sperm to penetrate the extracellular matrix that surrounds the egg. In the mouse: Data with native

neg: AKAP3 fibrous sheath in the principal piece of the sperm tail. It may function as a regulator of both motility- and head-associated functions such as capacitation and the acrosome reaction. AKAP3 has been shown to interact with: AKAP3 A-kinase anchor protein 3 is an enzyme that in humans is encoded by the "AKAP3" gene. The A-kinase anchor proteins (AKAPs) are a group of structurally diverse proteins, which have the common function of binding to the regulatory subunit of protein kinase A (PKA) and confining the holoenzyme to discrete locations within the cell. This gene encodes a member of the AKAP family,

neg: ZP3 binding and stimulation of the sperm acrosome reaction. The nascent protein contains a N-terminal signal peptide sequence, a conserved "ZP domain" module, a consensus furin cleavage site (CFCS), a polymerization-blocking external hydrophobic patch (EHP), and a C-terminal transmembrane domain. Cleavage at the CFCS separates the mature protein from the EHP, allowing it to incorporate into nascent ZP filaments. A variation in the last exon of this gene has previously served as the basis for an additional ZP3 locus; however, sequence and literature review reveals that there is only one full-length ZP3 locus in the human genome. Another locus encoding a

neg: Paragordius varius releases his sperm immediately. However, if the sperm does not land on the appropriate posterior area of the female, conception does not occur. When conception does occur, "P. varius" lay eggs, which comes out in a long, white, spaghetti-like string. These eggs are hatched into free-swimming larvae and must find an intermediate host, such as freshwater snails, mosquito larvae, or other small aquatic critters, to infect within a few days or they will die. Upon infection of one of these hosts, the larva takes about 5–14 days to develop into a cyst. At this stage it is ready to infect

neg: Spermatozoon and the exposure of enzymes attached to the inner acrosomal membrane of the sperm. This occurs after the sperm first meets the egg. This lock-and-key type mechanism is species-specific and prevents the sperm and egg of different species from fusing. There is some evidence that this binding is what triggers the acrosome to release the enzymes that allow the sperm to fuse with the egg. ZP3, one of the proteins that make up the zona pellucida, then binds to a partner molecule on the sperm. Enzymes on the inner acrosomal membrane digest the zona pellucida. After the sperm penetrates the

neg: Reproductive system stimulates some of the ova to develop and grow. One ovum is released and it passes through the fallopian tube into the uterus. Hormones produced by the ovaries prepare the uterus to receive the ovum. It sita her and awaits the sperm for fertilization to occur. When this does not occur i.e. no sperm for fertilization, the lining of the uterus, called the endometrium, and unfertilized ova are shed each cycle through the process of menstruation. If the ovum is fertilized by sperm, it attaches to the endometrium and the fetus develops. Most mammal reproductive systems are similar, however, there

neg: Fertility testing semen testing and genetic testing, as other factors such as impotence are obvious. Semen can be tested for sperm count, sperm motility, sperm morphology, pH, volume, fructose content, and acrosome activity. Checks are also made to identify undescended testicles and retrograde ejaculation, along with medical history, such as cancer treatment, radiation, drug use, etc. In some cases the hamster zona-free ovum test may also be used to diagnose fertility. Genetic testing and chromosomal analysis can rule out some other causes of male infertility, such as Klinefelter syndrome. A recent study identified epigenetic patterns in male sperm that may contribute to

neg: Globozoospermia People with globozoospermia have normal physical and mental development, normal clinical features and normal hormonal profile. The presence of round headed sperm in a semen analysis sample confirms the diagnosis of globozoospermia. The lack of acrosome can be ascertained by a technique known as immunofluorescence. Until 1995, the only options for people with globozoospermia who wished to conceive were adoption or sperm donation. With the advancement of assisted reproductive techniques (ART) it is now possible for those with globozoospermia to conceive using their own sperm. The main technique used is intracytoplasmic sperm injection (ICSI) where fertilisation is achieved by a

neg: Globozoospermia Globozoospermia Globozoospermia (also known as round-headed sperm syndrome) is a rare and severe form of monomorphic teratozoospermia. This means that the spermatozoa show the same abnormality, and over 85% of spermatozoa in sperm have this abnormality. Globozoospermia is responsible for less than 0.1% of male infertility. It characterised by round-headed spermatozoa without acrosome, an abnormal nuclear membrane and midpiece defects. Affected males therefore suffer from either reduced fertility or infertility. Studies suggest that globozoospermia can be either total (100% round-headed spermatozoa without acrosomes) or partial (20-60% round acrosomeless spermatozoa with normal sperm also identified in the sperm count,) however it

neg: Teratospermia Teratospermia Teratospermia or teratozoospermia is a condition characterized by the presence of sperm with abnormal morphology that affects fertility in males. The causes of teratozoospermia are unknown in most cases. However, Hodgkin's disease, coeliac disease, and Crohn's disease may contribute in some instances. Lifestyle and habits (smoking, toxin exposure, etc.) can also cause poor morphology. Varicocele is another condition that is often associated with decreased normal forms (morphology). In cases of globozoospermia (sperm with round heads), the Golgi apparatus is not transformed into the acrosome that is needed for fertilization. The presence of abnormally-shaped sperm can negatively affect fertility by

neg: Embryogenesis single sperm. Slow block begins the first few seconds after fertilization and is when the release of calcium causes the cortical reaction, various enzymes releasing from cortical granules in the eggs plasma membrane, to expand and harden the outside membrane, preventing more sperm from entering. Cell division with no significant growth, producing a cluster of cells that is the same size as the original zygote, is called cleavage. At least four initial cell divisions occur, resulting in a dense ball of at least sixteen cells called the morula. The different cells derived from cleavage, up to the blastula stage, are

neg: Sand lizard occur. Active selection of sperm by females appears to occur in a manner that enhances female fitness. On the basis of this selective process, the sperm of males that are more distantly related to the female are preferentially used for fertilization, rather than the sperm of close relatives. This preference may enhance the fitness of progeny by reducing inbreeding depression. Sand lizard The sand lizard ("Lacerta agilis") is a lacertid lizard distributed across most of Europe and eastwards to Mongolia. It does not occur in the Iberian peninsula or European Turkey. Its distribution is often patchy. The sand lizard is

neg: Acrosin which is protonated through His-57. Finally, His-57 deprotonates a water molecule, which can then serve as a nucleophile by similarly reacting with the carbonyl carbon. Collapse of the tetrahedral intermediate then results in a Ser-195 leaving group, which is protonated through His-57, resulting in all residues returned to their pre-catalytic state, and a carboxylic acid where there was previously a peptide bond. Acrosin is the major proteinase present in the acrosome of mature spermatozoa. It is stored in the acrosome in its precursor form, proacrosin. Upon stimulus, the acrosome releases its contents onto the zona pellucida. After this reaction occurs,

neg: Acrosin virus-inoculated lymphocytes. This suggests the further role of acrosin inhibitors as potentially viable agents in the prevention of HIV transmission. Acrosin Acrosin is a digestive enzyme that acts as a protease. In humans, acrosin is encoded by the "ACR" gene. Acrosin is released from the acrosome of spermatozoa as a consequence of the acrosome reaction. It aids in the penetration of the Zona Pellucida. Acrosin is a typical serine proteinase with trypsin-like specificity. The reaction proceeds according to the usual serine protease mechanism. First, His-57 deprotonates Ser-195, allowing it to serve as a nucleophile. Deprotonated Ser-195 then reacts with the

neg: Acrosin Acrosin Acrosin is a digestive enzyme that acts as a protease. In humans, acrosin is encoded by the "ACR" gene. Acrosin is released from the acrosome of spermatozoa as a consequence of the acrosome reaction. It aids in the penetration of the Zona Pellucida. Acrosin is a typical serine proteinase with trypsin-like specificity. The reaction proceeds according to the usual serine protease mechanism. First, His-57 deprotonates Ser-195, allowing it to serve as a nucleophile. Deprotonated Ser-195 then reacts with the carbonyl carbon of a peptide, forming a tetrahedral intermediate. The tetrahedral intermediate then collapses, resulting in an HN-R leaving group,

neg: Sexual reproduction one sex and changing to the other. In at least one hermaphroditic species, self-fertilization occurs when the eggs and sperm are released together. Internal self-fertilization may occur in some other species. One fish species does not reproduce by sexual reproduction but uses sex to produce offspring; "Poecilia formosa" is a unisex species that uses a form of parthenogenesis called gynogenesis, where unfertilized eggs develop into embryos that produce female offspring. "Poecilia formosa" mate with males of other fish species that use internal fertilization, the sperm does not fertilize the eggs but stimulates the growth of the eggs which develops into

neg: Wrinkle-faced bat to be both polyestrous and asynchronous, pregnant females have been recorded every month between January and August except May. Males emit a musky odour from the chin area to attract females. Their sperm morphology is unique in that the sperm head has a rounded nucleus and extremely pointed acrosome. "C. senex" subsp. "senex" is found in Belize, Colombia, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama and Venezuela. "C. senex" subsp. "greenhalli" is only found in Trinidad and Tobago. The binomial name "Centurio senex" is formed from the Latin "centurio" meaning division into hundreds and "senex" referring to old

neg: Male infertility Male infertility Male infertility refers to a male's inability to cause pregnancy in a fertile female. In humans it accounts for 40–50% of infertility. It affects approximately 7% of all men. Male infertility is commonly due to deficiencies in the semen, and semen quality is used as a surrogate measure of male fecundity. Factors relating to male infertility include: Antisperm antibodies (ASA) have been considered as infertility cause in around 10–30% of infertile couples. ASA production are directed against surface antigens on sperm, which can interfere with sperm motility and transport through the female reproductive tract, inhibiting capacitation and acrosome

neg: Globozoospermia also looks at causing oocyte activation in conjunction with ICSI, this time using spermatic binding-proteins, phospholipase C zeta (PLCζ) and postacrosomal sheath WW domain binding protein (PAWP). Globozoospermia Globozoospermia (also known as round-headed sperm syndrome) is a rare and severe form of monomorphic teratozoospermia. This means that the spermatozoa show the same abnormality, and over 85% of spermatozoa in sperm have this abnormality. Globozoospermia is responsible for less than 0.1% of male infertility. It characterised by round-headed spermatozoa without acrosome, an abnormal nuclear membrane and midpiece defects. Affected males therefore suffer from either reduced fertility or infertility. Studies suggest that

neg: Human reproduction a sperm may penetrate and merge with the egg, fertilizing it with the help of certain hydrolytic enzymes present in the acrosome. The fertilization usually occurs in the oviducts, but can happen in the uterus itself. The zygote then becomes implanted in the lining of the uterus, where it begins the processes of embryogenesis and morphogenesis. When the fetus is developed enough to survive outside of the uterus, the cervix dilates and contractions of the uterus propel it through the birth canal, which is the vagina. The ova, which are the female sex cells, are much larger than the spermatozoon

neg: Intracytoplasmic sperm injection some men who have no spermatozoa in the ejaculate (azoospermia) and in whom spermatozoa cannot be obtained surgically from the testicles. This condition is called nonobstructive or secretory azoospermia, as opposed to obstructive azoospermia, in which complete sperm production does occur in the testicles, and potentially fertilizing spermatozoa can be obtained by testicular sperm extraction (TESE) and used for ICSI. In cases of nonobstructive (secretory) azoospermia, on the other hand, testicular sperm production is blocked at different stages of the process of sperm formation (spermatogenesis). In those men in whom spermatogenesis is blocked at the stage of round spermatids, in

neg: GPX5 GPX5 Glutathione peroxidase 5 (GPx-5), also known as epididymal secretory glutathione peroxidase is an enzyme that in humans is encoded by the "GPX5" gene. GPx-5 belongs to the glutathione peroxidase family. It is specifically expressed in the epididymis in the mammalian male reproductive tract, and is androgen-regulated. Unlike mRNAs for other characterized glutathione peroxidases, this mRNA does not contain a selenocysteine (UGA) codon. Thus, the encoded protein is selenium-independent, and has been proposed to play a role in protecting the membranes of spermatozoa from the damaging effects of lipid peroxidation and/or preventing premature acrosome reaction. Alternatively spliced transcript variants encoding

neg: Sexual selection in scaled reptiles females. However, if females store sperm from a variety of sires, females can produce both sons and daughters with high fitness. When the female sand lizard "Lacerta agilis" mates with two or more males, sperm competition within the female's reproductive tract may occur. Active selection of sperm by females appears to occur in a manner that enhances female fitness. On the basis of this selective process, the sperm of males that are more distantly related to the female are preferentially used for fertilization, rather than the sperm of close relatives. This preference may enhance the fitness of progeny by reducing

neg: Parthenogenesis a human parthenogenetic stem cell line. Apomixis can apparently occur in "Phytophthora", an oomycete. Oospores from an experimental cross were germinated, and some of the progeny were genetically identical to one or other parent, implying that meiosis did not occur and the oospores developed by parthenogenesis. A form of asexual reproduction related to parthenogenesis is gynogenesis. Here, offspring are produced by the same mechanism as in parthenogenesis, but with the requirement that the egg merely be stimulated by the "presence" of sperm in order to develop. However, the sperm cell does not contribute any genetic material to the offspring. Since

neg: Squamata progeny. The WW females are likely produced by terminal automixis. When female sand lizards mate with two or more males, sperm competition within the females reproductive tract may occur. Active selection of sperm by females appears to occur in a manner that enhances female fitness. On the basis of this selective process, the sperm of males that are more distantly related to the female are preferentially used for fertilization, rather than the sperm of close relatives. This preference may enhance the fitness of progeny by reducing inbreeding depression. Recent research suggests that the evolutionary origin of venom may exist deep

neg: Mating of gastropods amputator because it prevents the amputee from mating again in the near future, which would result in sperm competition. The amputee is at least prevented from mating in the future as a male, which could divert resources from producing eggs with the amputator’s sperm. In addition to "Ariolimax" species, autoapophallation (self-amputation) has been documented in "Deroceras laeve". Here, it is a regular part of mating, although the penis does not get trapped in the other slug (as there is external sperm transfer), and may occur because the amputee’s penis retraction ability has been inhibited by the partner by transfer of

neg: Exoenzyme bacterial cell can be assessed using plate assays. Bacteria are streaked across the agar, and are left to incubate. The release of the enzyme into the surroundings of the cell cause the breakdown of the macromolecule on the plate. If a reaction does not occur, this means that the bacteria does not create an exoenzyme capable of interacting with the surroundings. If a reaction does occur, it becomes clear that the bacteria does possess an exoenzyme, and which macromolecule is hydrolyzed determines its identity. Amylase breaks down carbohydrates into mono- and disaccharides, so a starch agar must be used for

neg: Aerobic denitrification the intermediate species nitrous oxide (NO). A simple denitrification reaction proceeds as: The respiration reaction which utilizes oxygen as the oxidant is: Classically, it was thought that denitrification would not occur in the presence of oxygen since there seems to be no energetic advantage to using nitrate as an oxidant when oxygen is available. Experiments have since proven that denitrifiers are often facultative anaerobes and that aerobic denitrification does indeed occur in a broad range of microbial organisms with varying levels of productivity, usually lower productivity than results from purely aerobic respiration. The advantages of being able to perform denitrification

neg: Nucleophilic substitution at the γ unsaturated carbon in place of the carbon bearing the leaving group. This may be seen in the reaction of 1-chloro-2-butene with sodium hydroxide to give a mixture of 2-buten-1-ol and 1-buten-3-ol: The Sn1CB mechanism appears in inorganic chemistry. Competing mechanisms exist. In organometallic chemistry the nucleophilic abstraction reaction occurs with a nucleophilic substitution mechanism. Nucleophilic substitution via the S1 or S2 mechanism does not generally occur with vinyl or aryl halides or related compounds. Under certain conditions nucleophilic substitutions may occur, via other mechanisms such as those described in the nucleophilic aromatic substitution article. When the substitution

neg: Lepidoptera genitalia in which sperm is received, transported and stored. The oviducts of the female join together to form a common duct (called the 'oviductus communis') which leads to the vagina. When copulation takes place, the male butterfly or moth places a capsule of sperm (referred to as 'spermatophore') in a receptacle of the female (called the 'corpus bursae'). The sperm, when released from the capsule, swims directly into or via a small tube into a special seminal receptacle (called 'spermatheca'), where the sperm is stored until it is released into the vagina for fertilisation during egg laying, which may occur hours,

neg: Cortical reaction Cortical reaction The cortical reaction is a process initiated during fertilization by the release of cortical granules from the egg, which prevents polyspermy, the fusion of multiple sperm with one egg. In contrast to the fast block of polyspermy which immediately but temporarily blocks additional sperm from fertilizing the egg, the cortical reaction gradually establishes a permanent barrier to sperm entry and functions as the main part of the slow block of polyspermy in many animals. To create this barrier cortical granules, specialized secretory vesicles located within the egg's cortex (the region directly below the plasma membrane), are fused with

neg: Adverse vaccine reactions in pets reaction to vaccine allergy is very rare in dogs. When it does occur, however, anaphylaxis is a life-threatening emergency. More often, dogs will develop urticaria, or hives within minutes of receiving a vaccine. When this occurs, a veterinarian will treat the reaction with antihistamines and corticosteroid drugs and this is usually effective. Future vaccine protocols must be modified according to the vaccine component suspected to have triggered the reaction. FVRCP vaccines have also come under scrutiny of late due to possible risks to long term health. A study at Colorado State University noted an association between vaccination with parenteral (injectable)

neg: Glycolysis 2 new molecules have now been synthesized. This step, one of the two substrate-level phosphorylation steps, requires ADP; thus, when the cell has plenty of ATP (and little ADP), this reaction does not occur. Because ATP decays relatively quickly when it is not metabolized, this is an important regulatory point in the glycolytic pathway. ADP actually exists as ADPMg, and ATP as ATPMg, balancing the charges at -5 both sides. "Cofactors:" Mg Phosphoglycerate mutase isomerises 3-phosphoglycerate into 2-phosphoglycerate. Enolase next converts 2-phosphoglycerate to phosphoenolpyruvate. This reaction is an elimination reaction involving an E1cB mechanism. "Cofactors:" 2 Mg: one "conformational" ion

neg: Reaction progress kinetic analysis the intercepting reaction (designed to mimic the amount of product expected to be present in the parent reaction at the same substrate concentration). A perfect overlay of the rate vs. substrate concentration plots under same-excess-same product conditions indicates that product inhibition does occur under the reaction conditions used. While the failure of the rate vs. substrate concentration plots to overlay under same-excess-same product conditions does not preclude product inhibition, it does, at least, indicate that other catalyst deactivation paths must also be active. Same-excess experiments probing catalyst deactivation and product inhibition are among the most widely used applications of reaction

neg: Germ cell testicles and go on continuously. Spermatogonia are immature germ cells. They proliferate continuously by mitotic divisions around the outer edge of the seminiferous tubules, next to the basal lamina. Some of these cells stop proliferation and differentiate into primary spermatocytes. After they proceed through the first meiotic division, two secondary spermatocytes are produced. The two secondary spermatocytes undergo the second meiotic division to form four haploid spermatids. These spermatids differentiate morphologically into sperm by nuclear condensation, ejection of the cytoplasm and formation of the acrosome and flagellum. The developing male germ cells do not complete cytokinesis during spermatogenesis. Consequently, cytoplasmic

neg: Exercise induced anaphylaxis redness and itching. In the early stage, generalised urticaria develops. If the reaction does not diminish, it may become fully developed EIAn, in which gastrointestinal symptoms and constriction of the airway may occur. The late phase, which follows recovery from the reaction, includes frontal headaches and a feeling of fatigue; these symptoms may manifest themselves up to 72 hours following onset of the reaction. Cardiovascular symptoms are reported in 1/3 of patients diagnosed with EIAn. Food-Dependent Exercise-Induced Anaphylaxis (FDEIAn) is a subcategory of the disorder where exercise only invokes a reaction when followed by the ingestion of a food allergen.

neg: Zona pellucida Zona pellucida The zona pellucida (plural zonae pellucidae, also egg coat or pellucid zone) is a glycoprotein layer surrounding the plasma membrane of mammalian oocytes. It is a vital constitutive part of the oocyte. The zona pellucida first appears in unilaminar primary oocytes. It is secreted by both the oocyte and the ovarian follicles. The zona pellucida is surrounded by the cumulus oophorus. The cumulus is composed of cells that care for the egg when it is emitted from the ovary. This structure binds spermatozoa, and is required to initiate the acrosome reaction. In the mouse (the best characterised mammalian

neg: Zona pellucida human protein are not currently available. Zona pellucida The zona pellucida (plural zonae pellucidae, also egg coat or pellucid zone) is a glycoprotein layer surrounding the plasma membrane of mammalian oocytes. It is a vital constitutive part of the oocyte. The zona pellucida first appears in unilaminar primary oocytes. It is secreted by both the oocyte and the ovarian follicles. The zona pellucida is surrounded by the cumulus oophorus. The cumulus is composed of cells that care for the egg when it is emitted from the ovary. This structure binds spermatozoa, and is required to initiate the acrosome reaction. In

neg: Sperm competition Sperm competition Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring. Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase males' chance of reproductive success. Sperm competition results in a sexual conflict of interest between males and

neg: Darzens reaction new carbon–carbon bond. These first two steps are similar to a base-catalyzed aldol reaction. The oxygen anion in this aldol-like product then does an intramolecular S2 attack on the formerly-nucleophilic halide-bearing position, displacing the halide to form an epoxide. This reaction sequence is thus a condensation reaction since there is a net loss of HCl when the two reactant molecules join. The primary role of the ester is to enable the initial deprotonation to occur, and other carbonyl functional groups can be used instead. If the starting material is an α-halo amide, the product is an α,β-epoxy amide. If an

neg: Fertilisation a receptor on the sperm and causes the acrosomal reaction. The acrosomal vesicles of the sperm fuse with the plasma membrane and are released. In this process, molecules bound to the acrosomal vesicle membrane, such as bindin, are exposed on the surface of the sperm. These contents digest the jelly coat and eventually the vitelline membrane. In addition to the release of acrosomal vesicles, there is explosive polymerisation of actin to form a thin spike at the head of the sperm called the acrosomal process. The sperm binds to the egg through another ligand reaction between receptors on the vitelline

neg: Cysteine-rich secretory protein venom ophanin, for example, has 16 strictly conserved cysteines in addition to 8 disulfide bonds. CRISPs are found in the testes and epididymis of mammals, and are also involved in the process of fertilisation. In the spermatogenesis process (development of the spermatozoa in the testis), the CRISP2 protein is incorporated into the acrosome where it is believed to be involved in the adhesion of germ cells with Sertoli cells. CRISP2 also forms part of the sperm tail where it is thought to be involved in regulating flagellar beating. Proteins CRISP1 and CRISP4 are both found in the epididymis where they

neg: Acrosin binding protein Acrosin binding protein Acrosin binding protein is a protein that in humans is encoded by the ACRBP gene. The protein encoded by this gene is similar to proacrosin binding protein sp32 precursor found in mouse, guinea pig, and pig. This protein is located in the sperm acrosome and is thought to function as a binding protein to proacrosin for packaging and condensation of the acrosin zymogen in the acrosomal matrix. This protein is a member of the cancer/testis family of antigens and it is found to be immunogenic. In normal tissues, this mRNA is expressed only in testis, whereas it

neg: Acrosin binding protein is detected in a range of different tumor types such as bladder, breast, lung, liver, and colon. Acrosin binding protein Acrosin binding protein is a protein that in humans is encoded by the ACRBP gene. The protein encoded by this gene is similar to proacrosin binding protein sp32 precursor found in mouse, guinea pig, and pig. This protein is located in the sperm acrosome and is thought to function as a binding protein to proacrosin for packaging and condensation of the acrosin zymogen in the acrosomal matrix. This protein is a member of the cancer/testis family of antigens and it

neg: V-ATPase of insects, and certain tumor cells. Plasma membrane V-ATPases are involved in processes such as pH homeostasis, coupled transport, and tumor metastasis. V-ATPases in the acrosomal membrane of sperm acidify the acrosome. This acidification activates proteases required to drill through the plasma membrane of the egg. V-ATPases in the osteoclast plasma membrane pump protons onto the bone surface, which is necessary for bone resorption. In the intercalated cells of the kidney, V-ATPases pump protons into the urine, allowing for bicarbonate reabsorption into the blood. The yeast V-ATPase is the best characterized. There are at least 13 subunits identified to form

neg: ZP2 ZP2 Zona pellucida sperm-binding protein 2 is a protein that in humans is encoded by the "ZP2" gene. The zona pellucida is an extracellular matrix that surrounds the oocyte and early embryo. It is composed primarily of three (mouse) or four (human) glycoproteins (ZP1-4) with various functions during fertilization and preimplantation development. The protein encoded by this gene is a structural component of the zona pellucida and functions in secondary binding and penetration of acrosome-reacted spermatozoa. The nascent protein contains a N-terminal signal peptide sequence, a conserved ZP domain, a consensus furin cleavage site, and a C-terminal transmembrane domain. It

neg: Epigenetics of human development that imprinting may help protect the female from ovarian trophoblastic disease and parthenogenesis. Trophoblastic disease occurs when a sperm fertilizes an egg with no nucleus and a cancer-like mass forms in the placenta. Parthenogenesis occurs when an unfertilized egg develops into a fully functional organism that is genetically identical to the parent, who is female in the case of animals or both sexes, in the case of plants. This does not occur naturally in mammals. In most animals, especially mammals, uniparental inheritance of chromosomes is often lethal or results in developmental abnormalities, sometimes physically but often cognitively. Other hypotheses point

neg: Hook effect in serological tests for Brucellosis. The serological test is mainly seen in the precipitation reaction. The antibody that fails to react is known as the blocking antibody and prevents the precipitating antibody from binding to the antigens. Thus the proper precipitation reaction does not take place. However, when the serum is diluted, the blocking antibody is as well and its concentration decreases enough for the proper precipitation reaction to occur. Hook effect The hook effect or the prozone effect is a type of interference which plagues certain immunoassays and nephelometric assays, resulting in false negatives or inaccurately low results. Other

neg: Chondrocladia lyra for filaments and terminal balls. The terminal balls are relatively large, spherical casings full of spermatophores that can fertilize other harp sponges. The spermatophores are released by the terminal balls, and sigmas protruding from the sperm are caught by protruding isochelae on the filaments. The wide frame of "C. lyra" optimizes the chances for successful fertilization. It allows the sponge's sperm to have a wider range when traveling downstream. The harp sponge is also better at catching sperm, due to the widened stolons thoroughly lined with filaments. When the filaments snare spermatophores, they fuse with the recipient tissues. This reaction