Immunocytochemical localization of phospholipase A2 in hamster spermatozoa

Antibodies raised against porcine pancreatic phospholipase A2 (PLA2) react in immunoblottings with both the antigen as well as with one protein band of about 14 kDa from hamster spermatozoa extracts. Immunoblottings of proteins extracted from spermatozoon head and tail fractions also show similar results. Anti-PLA2 purified IgGs were employed for light and electron microscopic immunocytochemistry in order to detect PLA2 in hamster cauda epididymal spermatozoa. When whole mount spread spermatozoa were used under light (employing the PAP complex) or electron microscopy (using anti-rabbit gold conjugated), the acrosomal area of the gametes shows a noticeable labelling; a characteristic which is not observed in samples treated with the pre-immune serum. Immunocytochemistry undertaken in ultrathin sections from spermatozoon samples embedded in Lowicryl, demonstrates that the antigen appears preferentially distributed in the acrosome. Besides, sperm tails showed a scattered distribution of gold granules in the mitochondria of the midpiece. Results suggest that the antibody used recognizes a PLA2 which is preferentially located in the acrosome and mitochondria. On the other hand, the presence of a surface PLA2 in the plasma membrane covering the acrosome is suggested. This surface PLA2 would be probably related to the acrosome reaction phenomenon that occurs in the spermatozoon before penetrating the oocyte.