Mouse antral oocytes regulate preantral granulosa cell ability to stimulate oocyte growth in vitro

In this study we evaluated whether mouse oocytes derived from early antral or preovulatory follicles could affect the ability of preantral granulosa c ells to sustain oocyte growth in vitro. We found that early antral oocytes with a diameter greater than or equal to 75 mum did not grow any further du ring 3 days of culture on preantral granulosa cell monolayers in vitro, whi le most of the oocytes with a smaller diameter increased significantly in s ize. Similarly, about 65% of growing oocytes isolated from preantral follic les grew when cultured on preantral granulosa cells. By coculturing with gr owing oocytes fully grown early antral or preovulatory oocytes, a small pro portion (about 10%) of growing oocytes increased ill diameter, and changes in granulosa cell morphology were observed. Such effects occurred as a func tion of the fully grown oocyte number seeded and were not associated with a decrease in coupling index values. By avoiding physical contact between an tral oocytes and granulosa cells, the proportion of growing oocytes undergo ing a significant increase in diameter was about 36%. These results indicat e that fully grown mouse oocytes can control preantral granulosa cell growt h-promoting activity through the production of a soluble factor(s) and the maintenance of functional communications with surrounding granulosa cells. (C) 2001 Academic Press.