Sperm–egg interaction is mediated by a sperm‐associated body in quail

The present study describes the holes in the inner vitelline membrane of fertile eggs of the quail Coturnix japonica, which remain after the spermatozoa pass through. It was shown that the light‐microscopically observable ‘holes’ correspond mostly to electron‐microscopically defined ‘disks’, and, to a lesser extent (about 5%), real holes. Immunofluorescent staining of the vitelline membranes with an antiquail ZPC antiserum was used to discriminate the holes from the disks light‐microscopically. Over 96% of holes were accompanied by calcium‐coated sperm‐associated bodies, indicating a close relationship between the two. There was no preferential localization of the disks, holes or sperm‐associated bodies in the vitelline membrane around the egg. The sperm‐associated bodies bound with the spermatozoa at the posterior end of sperm flagella. Incubation of the inner vitelline membranes, isolated from the largest follicles, with spermatozoa resulted in production only of the disks, whereas the holes (about 9%) were produced when the sperm‐associated bodies were added to the system. It was suggested that the sperm‐associated bodies assist fertile spermatozoa in binding to the inner vitelline membrane, making holes in the membrane and passing through them in fertile eggs.