Oocyte Binding Research Articles

Aminopeptidase-like Protease Released from Oocytes Affects Oocyte Surfaces and Suppresses the Acrosome Reaction in Establishment of Polyspermy Block in Oocytes of the MusselMytilus edulis

Suppression of the acrosome reaction of sperm on fertilized oocytes inhibits sperm–oocyte binding and is considered one of the three mechanisms responsible for polyspermy block in oocytes of the musselMytilus edulis(Togoet al.,1995). When unfertilized oocytes were inseminated in the presence of aminopeptidase inhibitors and the fertilized oocytes were inseminated again, neither the acrosome reaction nor sperm binding to fertilized oocytes were suppressed, suggesting that aminopeptidase-like protease participates in suppression of the acrosome reaction. The supernatant solution obtained after centrifuging a suspension of fertilized oocytes hydrolyzed aminopeptidase substrates, and these activities were inhibited strongly or effectively by aminopeptidase inhibitors. When unfertilized oocytes were incubated with this supernatant solution and inseminated, both the number of sperm bound and the acrosome reaction rate decreased, and these effects were reversed by conducting this treatment in the presence of aminopeptidase inhibitors. These results suggest that aminopeptidase-like protease released from the oocyte at fertilization affects the oocyte surface to suppress the acrosome reaction and consequently inhibits sperm–oocyte binding.

Modulation of serotonin binding sites in spisula solidissima oocytes by phorbol ester

In Spisula solidissima oocytes, serotonin (5-hydroxytryptamine, 5-HT)-dependent meiosis reinitiation is mediated via specific 5-HT membrane binding sites. This oocyte response is inhibited by the phorbol ester TPA. To assess whether the inhibitory effect of TPA was due to alteration of oocyte membrane binding sites, we studied their characteristics after TPA treatment. [ 3H]-5HT binding assays revealed that TPA decreased the affinity and, after prolonged treatment, increased the number of oocyte binding sites. Moreover, inhibitory actions of TPA on 5-HT-induced meiosis reinitiation paralleled its inhibitory effects on 5-HT binding site affinity. The inhibitory actions in biological assays were restricted to TPA (an inactive analog of TPA, TPA-met was inefficient) and were completely reversed by staurosporine. Our data thus suggest an inhibitory role for protein kinase C on oocyte 5-HT binding sites under physiological conditions.

Induction of the acrosome reaction in human spermatozoa by a fraction of human follicular fluid

AbstractHuman ejaculated spermatozoa were washed through a Percoll gradient, preincubated for 10 hr in a defined medium containing serum albumin, and then induced to undergo rapid acrosome reactions by addition of human follicular fluid or a Sephadex G‐75 column fraction of the fluid. Induction by follicular fluid did not occur when the spermatozoa were preincubated for only 0 or 5 hr. The reactions were detected by indirect immunofluorescence using a monoclonal antibody directed against the human sperm acrosomal region. The percentage of acrosomal loss counted by transmission electron microscopy agreed with that counted by immunofluorescence. The apparent molecular weight of the Sephadex G‐75 fraction containing the peak of acrosome reaction‐inducing activity was 45,000 ± 4,200 (SD). The occurrence of physiological acrosome reactions was supported by: assessing motility (no significant loss of motility occurred during the treatment period when sperm were preincubated with bovine serum albumin), transmission electron microscopy (the ultrastructural criteria for the acrosome reaction were met), and zona‐free hamster oocyte binding and penetration (spermatozoa pretreated with the active fraction of follicular fluid, then washed and incubated with oocytes, showed significantly greater binding to and penetration of oocytes). The stimulation of the acrosome reaction by follicular fluid is apparently not due to blood serum contamination; treatment of preincubated spermatozoa with sera from the follicular fluid donors had no effect on the spermatozoa. The nature of the active component(s) in that fraction is currently being investigated.