Figure 2. A schematic of the spatial and temporal expression of local organizing factors in the transition of primordial follicles to primary follicles. The generation of primordial germ cells is dependent on the expression of the organizers Bmp4 and Bmp8b coming from somatic, extraembryonic ectoderm. Gonadogenesis is dependent on the migration of the germ cells to the gonadal ridge and the expression of specific factors in the indifferent cells of the presumptive gonad. Primary follicles are established by the appearance of the Figα-dependent transcription of zona pellucida proteins (ZP1,2,3), an extracellular matrix that defines and organizes the granulosa cells around the oocyte. The next layer of complexity involves the formation of the basal lamina, another extracellular matrix upon which the theca cells are organized, a process controlled in part by the oocyte-derived TGFß molecule, GDF-9. The potential sites of action of GDF-9 are indicated by the heavy yellow arrows and are discussed in the text. At this time the granulosa cells also express MIS, FSH-receptor and IGF-1/IGF-1 receptor, and cyclin D2. In response to the activation of these molecules granulosa cells proliferate, albeit slowly.
Source: Endocrinology 2001 Jun;142(6):2184-93
Edited by Aldo Campana,