The acrosome is a characteristic organelle of spermatids and sperm playing an important role in fertilization. Acrosomal hydrolases allow the sperm to penetrate through the layers surrounding the oocyte and are also involved in the sperm-oocyte recognition (1). Recently, the acrosome has been considered as a specialized type of secretory granule (2). As opposed to lysosomes, the molecular machinary of targeting of proteins to secretory granules has not been thoroughly investigated (3). The Golgi complex of early spermatids is involved in acrosome formation. Previous morphological studies indicate that the TGR of this cell type contains uncoated and clathrin-coated vesicles and tubules (2). Clathrin-coated vesicles might be involved in the anterograde transport of acrosomal enzymes form the Golgi apparatus to the acrosome. Recent studies from our group indicated that the TGR of early spermatids also contains COP-coated vesicles which are different to those typically found at the cis golgi side (4). The role of this novel type of vesicles is unknown. However, COP-coated buds have been described at the acrosomal membrane suggesting a role in acrosome biogenesis.
(1) Yanagimachi R, In: The Physiology of Reproduction, Raven Press, NY (1994) (2) Mart!nez-Men rguez et al., J. Histochem. Cytochem. 44: 313-329 (1996) (3) Arvan P & Castle D, Trends Cell Biol. 2:327-331 (1994) (4) Mart!nez-Men rguez et al., Eur. J. Cell Biol, in press (1996)