The combination of acrosome and acrosomal vesicle
formed the acrosomal system, usually referred to as acrosome.
The acrosome reaction consists of two steps--polymerization and lengthening of the acrosomal process with subsequent exocytosis of the acrosomal vesicle
, which exposes bindin; bindin then coats the acrosomal process and aids in sperm-egg attachment and fusion.
A cap-shaped acrosomal vesicle with condensing acrosomal material covered its apical portion.
6c, d, h-j) and the posterior portion of the acrosomal vesicle (Fig.
Sperm in contact with the jelly coat do not undergo an acrosome reaction involving exocytosis of the acrosomal vesicle, but in many instances they do undergo an elongation of the anterior portion of the acrosome [ILLUSTRATION FOR FIGURES 18, 19, 22 OMITTED].
Contact with the vitelline layer overlying the microvilli initiates the typical acrosome reaction, in which the outer acrosomal membrane and plasma membrane fuse at the apex and roll back in a manner that releases the contents of the acrosomal vesicle onto the vitelline layer [ILLUSTRATION FOR FIGURES 25, 26 OMITTED].
The lamprey, which is a cyclostome, has spermatozoa that carry a spherical acrosomal vesicle at the anterior end of their heads, subacrosomal material between the acrosome and the nucleus, and a long perforatorium rod through the nucleus (Follenius, 1965; Stanley, 1967; Nicander and Sjoden, 1971; Jaana and Yamamoto, 1981) [ILLUSTRATION FOR FIGURE 6B OMITTED].
The exocytosis of the acrosomal vesicle at several points in hagfish (our preliminary observation) as seen in higher vertebrates may be different from the acrosome reaction in sturgeon.
However, there was a significant decrease in sperm entry into the cytoplasm after binding by sperm that had lost their acrosomal vesicles
prior to binding.