CUMULUS CELL-FUNCTION DURING BOVINE OOCYTE MATURATION, FERTILIZATION,AND EMBRYO DEVELOPMENT IN-VITRO

Several contemporary micromanipulation techniques, such as sperm micro injection, nuclear transfer, and gene transfer by pronuclear injection , require removal of cumulus cells from oocytes or zygotes at various stages. In humans, the cumulus cells are often removed after 15-18 hr of sperm-oocyte coincubation to assist the identification of the ferti lization status. This study was designed to evaluate the function of c umulus cells during oocyte maturation, fertilization, and in vitro dev elopment in cattle. Cumulus cells were removed before and after matura tion and after fertilization for 0, 7, 20, and 48 hr. The cumulus-free oocytes or embryos were cultured either alone or on cumulus cell mono layers prepared on the day of maturation culture. Percentages of oocyt e maturation, fertilization, and development to cleavage, morula, and blastocyst stages and to expanding or hatched blastocysts were recorde d for statistical analysis by categorical data modeling (CATMOD) proce dures. Cumulus cells removed before maturation significantly reduced t he rate of oocyte maturation (4-26% vs. 93-96%), fertilization (0-9% v s. 91-92%), and in Vitro development at all stages evaluated. Cumulus cells removed immediately prior to in Vitro fertilization (IVF) or 7 h r after IVF reduced the rates of fertilization (58-60% and 71%, respec tively, vs. 91-92% for controls), cleavage development (40-47% and 53- 54% vs. 74-78% for controls), and morula plus blastocyst development(1 5% and 24% vs. 45%, P < 0.05). Cumulus cell co-culture started at Vari ous stages had no effect on fertilization and cleavage development but significantly improved rates of embryo development to morula or blast ocyst stages (P < 0.05). Cumulus cell removal at 20 hr after IVF resul ted in similar development to controls (P > 0.05) at all stages tested in this study. The intact state of surrounding cumulus cells of oocyt es or embryos appears to be beneficial before or shortly after insemin ation (at or before 7 hr of IVF) but not essential at 20 hr after IVF. (C) 1995 Wiley-Liss, Inc.