The ontogeny of nexuses (gap junctions) in the ovary of the fetal mouse

Nexuses (gap junctions), the morphological correlates of direct cell-to-cell communication, were consistently detected between granulosa cells of primordial follicles in the ovaries of adult cycling, juvenile, or neonatal mice. To examine the ontogeny of these intercellular channels, the cellular interactions occurring during the fetal stages of folliculogenesis, which culminate in the formation of primordial follicles, were analyzed in ovaries from fetal days 13, 15, 17, and 19. On fetal day 13, the ovary is characterized by clusters of germinal cells and invading rete ovarii cells. The rete cells progressively penetrate the ovary and wall off clusters of oocytes by fetal day 17, at which time rete cells can be recognized as presumptive granulosa cells. Gap junctional contacts can be recognized between rete cells on day 13 and these contacts persist as the cells become recognizable as presumptive granulosa cells throughout ovarian histogenesis. Quantification of junctional contacts from days 15-19 indicated that the number of gap junctions increases with fetal age. In addition heterocellular gap junctional contacts were detected between oocytes and presumptive granulosa cells as early as fetal day 17, indicating that the potential for direct intercellular communication between granulosa cells and oocytes is established from the earliest contact.