Number of Cortical Granules in Mouse Oocytes from Inbred Strains Differing in Efficiency of Fertilization

Abstract

The number of cortical granules was estimated in unfertilized oocytes of 4 inbred strains of mice (CBA/Kw C57BL/Kw, KP and KE) and F1 hybrids (Series 1). KE oocytes had significantly fewer cortical granules than the oocytes of the other strains and F1 hybrids. The largest number of cortical granules was found in CBA/Kw oocytes. The analysis of ovarian and tubal oocytes of KE and CBA/Kw strains before and during ovulation (from 9-13 h after human chorionic gonadotropin injection, Series II) revealed that in freshly ovulated KE oocytes some cortical granules extrude their contents into the perivitelline space. This premature cortical reaction may be partly responsible for the low efficiency of fertilization that characterizes the KE strain.