MODULATION OF SPERMATOZOA AND ZONA-PELLUCIDA PROPERTIES BY THE SOLUBLE ACROSOME REACTION-INDUCING FACTOR OF THE OVULATED EGG-CUMULUS COMPLEX

Three sources of hamster periovulatory fluids (+/- heat inactivation a t 56 degrees C), with bovine serum albumin (BSA) as control, were test ed for effects on penetration of three classes of eggs by hamster sper m precapacitated in BSA. These fluids were a soluble extract of cumulu s oophorus fluid (COF) from the ovulated hamster egg-cumulus complex, serum, and follicular fluid. Egg types were ovulated, salt-stored (ovu lated), and follicular. In both COF and serum, there were significant differences among egg types in mean penetration, and significant effec ts of fluid addition. In contrast, there was no effect of follicular f luid and no differences between follicular and stored eggs. For the fo llicular eggs (combined data, normalized, ranked), patterns of respons e to the three factors (+/- heating) were different: only unheated COF and heated serum increased penetration significantly above BSA contro l levels (average rank 20.2, 41.4, 38, for BSA, COF (unheated), serum (heated), respectively). This indicated that the active component in C OF was heat labile, not present in either serum or follicular fluid, a nd, therefore, of oviductal origin. Oviduct and/or COF exposure of egg s and sperm was tested for effects as an acrosome reaction inducing fa ctor (ARIF) for acrosome reactions (AR; zona-bound and free-swimming s perm) and on sperm:zona binding and penetration. The COF ARIF for free -swimming sperm AR was heat stable. Penetration of follicular eggs inc reased after incubation in COF prior to sperm addition, but a greater response occurred when COF was added to eggs with sperm. In kinetic ex periments, 25 min following sperm attachment, follicular eggs had lost 41% of initially bound sperm, vs. 23% for ovulated eggs, and had only 16 AR sperm/egg, vs. 26 for ovulated. Follicular eggs incubated in CO F (then washed three times) had the same number of bound AR sperm as o vulated eggs. Acid solubilized zona pellucida (ASZP) from ovulated egg s was more effective as an ARIF per zona than ASZP from follicular egg s. Zonae of follicular eggs, as evidenced by dissolution times in beta -mercaptoethanol (beta-MEOH), were not ''harder'' than those of ovulat ed eggs. There were differences in lectin binding antigens on zonae of both fresh and stored, follicular and ovulated, eggs. We conclude tha t multiple biological factors orchestrate sperm:egg interactions in th e ampulla. Our data are consistent with the presence of at least three effective components: 1) the oviductal lectin-binding antigen (ZPO or oviductin), 2) an additional heat-labile component, and 3) the heat-s table ARIF for free-swimming sperm. (C) 1994 Wiley-Liss, Inc.