A mammalian sperm is minute, microscopic, flagellated and motile gamete with no nutritive material, protective envelopes and most of cell- organelles like ribosome, endoplasmic reticulum, etc. The whole body of sperm is enveloped by plasma membrane only. It is small cap-like pointed structure present at the tip of nucleus. It is formed from a part of Golgi body of spermatid.
Role of actin cytoskeleton in mammalian sperm capacitation and the acrosome reaction
Polyspermy - Wikipedia
In human fertilization, the sperm introduces the centrosome-the microtubule organizing center-and microtubules are organized within the inseminated egg from the sperm centrosome. These microtubules form a radial array, the sperm aster, the functioning of which is essential for pronuclear movement for the union of the male and female genomes. We established functional assay for human sperm centrosomal function, by using heterologus ICSI system with bovine and rabbit eggs. After human sperm incorporation into mammalian egg, we observed that the sperm aster was organized from sperm centrosome, and the sperm aster enlarged as the sperm nuclei underwent pronuclear formation.
Fertilization: Sperm/Egg Recognition and Contact
In order to fertilize, the mammalian spermatozoa should reside in the female reproductive tract for several hours, during which they undergo a series of biochemical modifications collectively called capacitation. Only capacitated sperm can undergo the acrosome reaction after binding to the egg zona pellucida, a process which enables sperm to penetrate into the egg and fertilize it. Polymerization of globular G -actin to filamentous F -actin occurs during capacitation, depending on protein kinase A activation, protein tyrosine phosphorylation, and phospholipase D activation. F-actin formation is important for the translocation of phospholipase C from the cytosol to the sperm plasma membrane during capacitation. Prior to the occurrence of the acrosome reaction, the F-actin should undergo depolymerization, a necessary process which enables the outer acrosomal membrane and the overlying plasma membrane to come into close proximity and fuse.
During fertilization , a sperm must first fuse with the plasma membrane and then penetrate the female egg cell to fertilize it. Fusing to the egg cell usually causes little problem, whereas penetrating through the egg's hard shell or extracellular matrix can be more difficult. 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.