INHIBITION OF DOMESTIC CAT SPERMATOZOA ACROSOME REACTION AND ZONA-PELLUCIDA PENETRATION BY TYROSINE KINASE INHIBITORS

Spermatozoa from teratospermic domestic cats (> 60% morphologically ab normal spermatozoa per ejaculate) consistently exhibit lower levels of oocyte penetration in vitro than their normospermic (< 40% abnormal s permatozoa per ejaculate) counterparts. This could be caused by struct ural abnormalities or intracellular defects resulting in disruption of normal cellular functions. Spermatozoa from teratospermic cats also a ve compromised in the ability to capacitate and undergo the acrosome r eaction (AR) in vitro. Further, we recently identified two tyrosine ph osphorylated proteins (95- and 160-kDa) localized over the acrosome re gion in domestic cat spermatozoa. Phosphorylation of these proteins is reduced in teratospermic compared with normospermic ejaculates. To be gin to understand the relationship between tyrosine phosphorylation an d sperm function, we examined the effects of two protein tyrosine kina se inhibitors (tyrphostin RG-50864 and genistein) on (1) sperm motilit y; (2) protein tyrosine phosphorylation; (3) the ionophore A23187-indu ced AR; (4) the spontaneous and zona pellucida (ZP)-induced AR, and (5 ) the ability of spermatozoa from normospermic cats to penetrate consp ecific ZP-intact oocytes. Over a wide range of concentrations, neither inhibitor affected sperm percentage motility during incubation (P > 0 .05). Preincubation with either inhibitor reduced tyrosine phosphoryla tion of both (95- and 160-kDa) sperm proteins. Although both inhibitor s blocked the ZP-induced AR, neither influenced the spontaneous AR nor the A23187-induced AR, suggesting that tyrosine phosphorylation may b e involved in physiologic AR. No differences (P > 0.05) were observed in the ability of control or inhibitor-treated spermatozoa to bind to or penetrate the outer ZP layer. However, percentages of oocytes with treated spermatozoa in the inner ZP (tyrphostin, 8.7%; genistein, 20.4 %) and perivitelline space (tyrphostin, 0%; genistein, 2.3%) were less (P < 0.001) than untreated controls (inner ZP, 62.7%; perivitelline s pace, 10.2%). These results (1) demonstrate that ZP-induced acrosomal exocytosis in domestic cat spermatozoa is regulated via a tyrosine kin ase-dependent pathway and (2) suggest that defects in these Signaling pathways may represent one of the causes for compromised sperm functio n in teratospermic males. (C) 1998 Wiley-Liss, inc.