REGIONAL DIFFERENCES IN GRANULOSA-CELLS OF PREOVULATORY MEDAKA FOLLICLES

The regional differences in morphology and steroid production of granu losa cells of the animal and vegetal hemispheres of the preovulatory m edaka (Oryzias latipes) follicles were investigated. Granulosa cells i n the animal pole region were distinguishable from those in the vegeta l pole region in their shape and distribution. The distribution of tal l granulosa cells was more compact in the vegetal pole area than in th e remaining areas. The gonadotropin-induced production of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one by granulosa cells alone was at a level sufficient to induce in vitro maturation of the oocyte. Production wa s significantly greater in the vegetal hemisphere than in the animal h emisphere. These results indicate that medaka follicles have morpholog ical and physiological differences in granulosa cells corresponding to regional differences along the animal-vegetal axis of the oocyte.