Effect of removal of cumulus cells from one-cell mouse embryos on in vitro development

The effects of the removal of cumulus cells from fertilized mouse oocytes (one-cell embryos) and the presence of streptomycin in culture medium on in vitro development were studied. Ham's F-10 medium with (0.075 g/liter) or without streptomycin was supplemented with human serum (15%). Cumulus-intact embryos were harvested from oviducts after mice were superovulated with pregnant mare's serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG). Hyaluronidase (300 IU/ml) was used to remove the cumuli. Embryos were cultured (i) with cumulus/without streptomycin (n=238), (ii) with cumulus/with streptomycin (n=185), (iii) without cumulus/with streptomycin (n=210), and (iv) without cumulus/without streptomycin (n=218). Embryonic development was assessed 24, 96, and 120 hr after initiation of culture. Percentage two cells and percentage small or expanded blastocysts were not different (P>0.05) among experimental groups. Percentages hatched blastocysts for the four groups were (i) 36±8 and 54±7, (ii) 35±8 and 55±6, (iii) 19±5 and 42±6, (iv) 23±5 and 47±5 at 96 and 120 hr, respectively. Percentages all (small, expanded, and hatched combined) blastocysts were (i) 74±5 and 74±5, (ii) 74±9 and 72±5, (iii) 56±6 and 63±5, and (iv) 61±5 and 63±5 at 96 and 120 hr, respectively. A greater (P<0.05) percentage of embryos developed to blastocysts and hatched by 96 and 120 hr, when they were cultured with the cumulus intact. There was no effect of streptomycin on embryonic development. Cumulus cells may act as nurse cells during a critical stage of the development of the embryo.