Size of Perivitelline Space and Incidence of Polyspermy in Mouse Oocytes Treated with Tunicamycin

The perivitelline space is the gap between the plasma membrane and the zona pellucida of the oocyte. Although not present in the oocytes in the germinal vesicle stage, the perivitelline space is known to start forming when meiotic maturation resumes and to enlarge in matured oocytes at the metaphase II stage (Kaufman et al., 1989; Okada et al., 1993). Recently, it has been suggested that there is a relationship between the size of perivitelline space in porcine oocytes and the incidence of polyspermy in those following insemination (Funahashi et al., 1994; Wang et al., 1998), but it is not clear whether the relationship is present in oocytes of another animals. It is generally thought that glycoproteins synthesized and secreted by cumulus cel ls are involved in the enlargement of the perivitelline space (Talbot and Dandekar, 2003). Glycoproteins secreted from cumulus cells accumulate between cumulus cells and in the perivitelline space (Talbot, 1984). Hyaluronan, a major component of the glycoprotein synthesizd and secreted by cumulus cells, in particular has a water absorbing property which results in enlargement of the matrix of cumulus and the perivitelline space (Talbot and Dandekar, 2003). In the cumulus-oocyte complex (COC) with cumulus cells whose glycoprotein synthesis was inhibited, therefore, it is supposed that the perivitelline space in oocytes fails to enlarge and the incidence of polyspermy after insemination increases. In the present study, the size of the perivitelline space was measured in mouse oocytes treated with tunicamycin, an inhibitor of glycoprotein synthesis, and also the incidence of polyspermy in those following insemination was observed, in order to examine whether the relationship between the incidence of polyspermy and the size of perivitelline space exists in mouse oocytes.