Acrosome Reaction

In sea-urchin eggs lysins have been demonstrated which act on the jelly covering and vitelline membrane of the egg. Evidence of this is seen. In Hydroides, where the spermatozoa leave holes in the vitelline membrane as they pass through. The acrosome of mammalin sperms contains the enzyme hyaluranidase which helps the sperms to penetrate the corona radiata cells. The zona pellucida is penetrated by proteases. Penetration of the egg by the sperm is initiated by the acrosome reaction.



When the sperm comes into contact with the egg covering the apex of the acrosome breaks. Fusion of the sperm plasma membrane and the outer protion of the acrosomal membrane takes place at the break. The acrosomal membrane takes place at the break. The acrosomal granule with its lysins comes into contact with the egg envelope. Eversion of the wall of the acrosomal vesicle near the nucleus takes place and acrosomal tubules are formed, while in Arbacia, Asterias and Saccoglossus there is only a single acrosomal filaments. The sperm makes its way through the egg envelope with the help of lysins. The acrosomal tubules come into contact with the egg plasma membrane, and interdigitate with the membrane. The changes which take place in the acrosome tubules interdigitate with the egg plasma membrane, fusion to the two membranes takes place. The internal sperm organelles now come deeper within the egg cytoplasm. They move through the tunnel formed by the fusion the sperm and egg plasma membranes.


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