Detection of a soluble acrosome reaction‐inducing factor, different from serum albumin, associated with the ovulated egg‐cumulus complex

Abstract

Soluble extracts of the ovulated hamster egg-cumulus complex (ECC) were tested on capacitated sperm for activity in inducing the physiological acrosome reaction (AR). Evidence for occurrence of the physiological AR included enhanced sperm penetration of intact homologous zonae pellucidae as well as induction of AR in nonattached and in zona-bound sperm following a brief coincubation with test compound. Since hamster serum albumin, a major protein of hamster body fluids, also induces spontaneous ARs under certain conditions, it was used as one of the comparators for the acrosome reaction inducing factor (ARIF; Westrick et al., Biol Reprod 32 [Suppl 1]. 213, 1985) activity in the ECC. Sperm exposure to concentrations of the soluble ECC extract ranging from 0.04 to 0.2 mg protein/ml significantly increased penetration of salt-stored zonae by 36%, mean numbers of penetrating sperm by 90%, ARs in nonattached sperm by 65%, and ARs in zona-bound sperm by 102%. Hamster serum albumin added after completion of capacitation had no significant effect on these parameters. We conclude that 1) the ovulated ECC contains a soluble ARIF that augments zona-induced ARs and sperm penetration and 2) the ARIF is not serum albumin.

Fertilization Capacity of Mouse Oocytes Matured <i>In Vitro</i>: Effect of PMSG, FSH and Epidermal Growth Factor (EGF) in Serum-Free Maturation Medium

“…The importance of cumulusexpansion was also supported by the low fertilizability of cumulus-free oocytes in the present study and previous reports [17,18]. Boatman and Robbins [19] reported that a soluble factor, possibly bound to the surface of the cumulus cells, promoted the acrosome reaction and increased fertilization rate. Therefore, cumulus cells might secrete some factors promoting fertilization into the expanded cumulus matrix.…”

Identification of a Sperm Penetration Factor in the Oviduct of the Golden Hamster1

“…For egg penetration experiments, cauda epididymal sperm were obtained undiluted under oil and, afier staggering inseminations by 2-5 min, incubated under capacitating conditions (2-4 X 106/ml) for 5 h in medium TAW-WA with sperm motility factors as previously described [16,17,39,40]. Then sperm were diluted 1:10 into drops of TALP-PVA containing 14-16 follicular eggs + biological factors.…”

“…Cumulus oophorus fluid (COF) eluate was prepared as previously described [16,17]. OVN was isolated from excised oviducts of mature female hamsters (n = 6 hamsters per collection) that were injected with 25 IU of eCG (Diosynth, Chicago, IL) on the morning of the post-estrus discharge [34] and then killed by cervical dislocation at 1500 h on Day 4.…”

“…There is considerable interest in identifying molecules present at the site of in vivo fertilization that act as cofactors for penetration and fertilization, potentially acting as acrosome reaction-inducing factor(s) (ARIF; [13][14][15][16]). Previously, we reported that the ovulated hamster egg cumulus complex contained a soluble, non-albumin ARIF that stimulated hamster sperm acrosome reactions and enhanced penetration through the zona pellucida [13,16,17]. The egg penetration-enhancing substance for follicular oocytes appeared to be of oviductal origin and functioned partly to increase the ARIF and spermbinding activities of the zona pellucida [17].…”

“…This contrasts with the in vitro situation, in which large numbers of sperm per egg are required for efficient penetration and the penetrating sperm may remain bound to the zona pellucida for prolonged periods before undergoing the acrosome reaction [10,11] or entering into the perivitelline space [12]. There is considerable interest in identifying molecules present at the site of in vivo fertilization that act as cofactors for penetration and fertilization, potentially acting as acrosome reaction-inducing factor(s) (ARIF; [13][14][15][16]). Previously, we reported that the ovulated hamster egg cumulus complex contained a soluble, non-albumin ARIF that stimulated hamster sperm acrosome reactions and enhanced penetration through the zona pellucida [13,16,17].…”