Sperm enzyme dissolves egg

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During fertilization , a sperm must first fuse with the plasma membrane and then penetrate the female egg cell in order to fertilize it. Fusing to the egg cell 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 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.
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Egg Fertilization

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Unresolved Questions Concerning Mammalian Sperm Acrosomal Exocytosis

NCBI Bookshelf. Recognition of sperm by the vitelline envelope or zona pellucida is followed by the lysis of that portion of the envelope or zona in the region of the sperm head by the acrosomal enzymes Colwin and Colwin ; Epel This lysis is followed by the fusion of the sperm plasma membrane with the plasma membrane of the egg. The entry of a sperm into a sea urchin egg is illustrated in Figure 7. Sperm-egg binding appears to cause the extension of several microvilli to form the fertilization cone Summers et al. Homology between the egg and the sperm is again demonstrated, because the transitory fertilization cone, like the acrosomal process, appears to be extended by the polymerization of actin.
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How Sperm Get Hyperactive

In recent years, the study of mammalian acrosomal exocytosis has produced some major advances that challenge the long-held, general paradigms in the field. Principally, the idea that sperm must be acrosome-intact to bind to the zona pellucida of unfertilized eggs, based largely on in vitro fertilization studies of mouse oocytes denuded of the cumulus oophorus, has been overturned by experiments using state-of-the-art imaging of cumulus-intact oocytes and fertilization experiments where eggs were reinseminated by acrosome-reacted sperm recovered from the perivitelline space of zygotes. In light of these results, this minireview highlights a number of unresolved questions and emphasizes the fact that there is still much work to be done in this exciting field. Future experiments using recently advanced technologies should lead to a more complete and accurate understanding of the molecular mechanisms governing the fertilization process in mammals. The mammalian sperm is a highly polarized cell, consisting fundamentally of a head containing the male's genetic material in the condensed nucleus and a flagellum that provides the motive force to bring the sperm to the egg surface [ 1 ].
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This event occurs within the first 24 hours after the eggs have been released from the ovaries and can occur only if there are sperm present around the eggs at this critical time. The penetration of the egg by the sperm AND the resulting formation of the nucleus of the sperm and the nucleus of the egg within the interior of the egg is known as fertilization. In the Embryo lab, the eggs and sperm are combined by one of two processes, by insemination or by ICSI.
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