MODIFICATIONS OF THE MOUSE ZONA-PELLUCIDA DURING OOCYTE MATURATION - INHIBITORY EFFECTS OF FOLLICULAR-FLUID, FETUIN, AND ALPHA-2HS-GLYCOPROTEIN

Mouse oocyte maturation in vivo or in vitro is accompanied by a precoc ious release of cortical granules. When oocytes are matured in vitro i n the absence of serum, cortical granule exocytosis results in modific ations of the zona pellucida (ZP) that are known to constitute the zon a pellucida block to polyspermy. Fetuin, a glycoprotein found in newbo rn calf serum, can inhibit these maturation-associated changes in the zona pellucida. In this report we demonstrate that the human fetuin ho mologue, alpha2HS-glycoprotein, is present in human follicular fluid. Human follicular fluid, or purified human alpha2HS-glycoprotein, inhib its the maturation-associated conversion of mouse ZP2 to ZP2, in a con centration-dependent manner. Although the concentration of alpha2HS-gl ycoprotein in human follicular fluid is high enough to account for the inhibitory effect of human follicular fluid on this maturation-associ ated conversion, human follicular fluid immunodepleted of alpha2HS-gly coprotein retains its full inhibitory activity. Thus, other inhibitory molecules are likely to he present in follicular fluid and contribute to the inhibition of the maturation-associated conversion of ZP2.