THE ESTABLISHMENT OF FOLLICULAR DOMINANCE IN COCULTURED MOUSE OVARIANFOLLICLES

An in vitro model of dominant and subordinate ovarian follicles was de veloped to allow a closer investigation of the phenomenon of follicula r dominance. Preantral mouse ovarian follicles were cultured either al one or in pairs. Pairs of follicles were either in direct contact or i n shared medium, but without physical contact. The experiments showed that where contact was allowed to develop between follicles one follic le invariably became dominant, while the other would grow and develop little during the culture period. In contrast, there was no effect of co-culture on follicle development in the absence of contact between t he follicles. There was, therefore, no evidence of secretion of a diff usible factor by a dominant follicle that could affect the development of neighbouring follicles. After 6 days of co-culture with contact, h istological examination of the subordinate follicle showed that it was healthy, in spite of remarkably little growth during culture. In a fu rther experiment, the subordinate follicle was separated from the domi nant one after 2 days of co-culture (when a significant difference in size had already developed), and cultured alone. These 'released' foll icles exhibited a spurt of growth during the remaining culture period, attaining a size and appearance indistinguishable from those of contr ols by the end of culture. This confirms that the dominant follicle, w hile depressing the growth of its neighbour, is not inducing irreversi ble atresia in the subordinate follicle in this model. The in vitro mo del will allow a more detailed study of direct influences of dominant- subordinate follicle interactions, and should increase our knowledge o f a poorly understood phenomenon.