The vitelline coat spikes: a new peculiar structure of Mytilus galloprovincialis eggs with a role in sperm-egg interaction.

In the course of this study we found that in Mytilus galloprovincialis eggs long filamentous protrusions never described before, which we have termed "vitelline coat spikes," could be clearly detected using the lectin from Dolichos biflorus, which recognizes the GalNAc residues. The spikes could be also observed by transmission electron microscope but only in some fortuitous sections could their origin in the vitelline coat be clearly observed. The spikes were also clearly visible using the scanning electron microscope. Observations of the sperm-egg interaction very few seconds after insemination or using fixed eggs suggested that the spikes could play a role in a primary binding to the unreacted sperm. Experiments have been done to test the effect of GalNAc on the sperm-egg binding and on the fertilization process which seem to confirm this hypothesis.