PHENOTYPE AND MATURATION RATE OF OOCYTES OF CHIMERIC MICE PRODUCED FROM 2 STRAINS THAT DIFFER IN OOCYTE QUALITY

The oocytes of females from the inbred mouse strains KE (albino) and C BA (agouti) differ in the following characteristics: the appearance of the cytoplasm is clear in KE but granular in CBA; the cumulus oophoru s dispersion with hyaluronidase is quick in KE but slow in CBA; dissol ution of the zona pellucida with a proteolytic enzyme is slow in KE bu t quick in CBA; and the maturation stage at the time of ovulation is m etaphase I in KE while in CBA the first polar body has been extruded. Aggregation chimaeras were produced to investigate whether these diffe rences are intrinsic or extrinsic to developing oocytes. Among 13 fert ile chimaeric females, two produced only CBA oocytes, four produced bo th CBA and KE oocytes and were germline chimaeras, and seven produced only KE oocytes, as recognized by progeny testing. The larger number o f females producing KE oocytes is a result of strong selection against CBA germ cells. All chimaeric females had cumuli composed of both KE and CBA cells, as recognized by the time of dispersion and glucose pho sphate isomerase electrophoresis, but the presence of non-homologous c umulus cells did not change the character of the developing oocytes si gnificantly. The conclusion from this study is that the rate of meioti c maturation, sensitivity of oocyte investments to enzymes, and deposi tion of granules in ooplasm are determined largely autonomously by gen es acting in the germ cells.