Modulation of fertilization by the vitellus after interaction with peptides released by hamster sperm-zona pellucida contact

Two to three minutes after hamster sperm make contact with and adhere to the surface of homologous zonae pellucidae in vitro, the first of several sets of peptides (S1 peptides) is released into the supernatant. This release occurs whether the zonae have or have not been mechanically separated from the vitellus (cellular part of the egg). Presence of the S1 peptides is detected by means of a sperm-egg assay, the premature binding assay. This assay is based on the ability of an aliquot of the medium, in which sperm are interacting with the zona surface, to induce early binding, upon addition of the aliquot to a second drop of interacting gametes. To determine if the vitellus affected the 2-min S1 peptides the ultrafiltrates of the supernatants containing them, released through sperm-egg and sperm-zona interactions, were fractionated on Biogel P-6 and their elution profiles were compared using the premature binding assay. The sperm-egg ultrafiltrates were resolved into two main domains of activity, while those of the sperm-zona formed three. The ultrafiltrates collected 2 min after the interaction of sperm with eggs or with isolated zonae were compared for their abilities to inhibit the penetration of the zona pellucida, a previously demonstrated capacity of the 2-min sperm-egg S1 peptides. The ultrafiltrate containing the sperm-zona peptides, except at a very low level, failed to inhibit penetration significantly. However, when the sperm-zona ultrafiltrate was preincubated with eggs then the resulting supernatant inhibited penetration in a dose-related manner, and the three-domain elution profile, characteristic of the sperm-zona ultrafiltrate, was converted to the egg-like two-domain profile. Taken together these data suggest that the 2-min S1 peptides consist of several subpopulations, at least one of which interacts with the vitellus. The resulting solution then acquires the ability to inhibit penetration of the egg by the sperm in a dose-related manner. Taken together these data indicate that by interacting with at least one of the components of the 2-min peptides, the vitellus is involved in regulating sperm-zona interactions.