PROTEIN DISTRIBUTION AND GENE-EXPRESSION OF COLLAGEN TYPE-IV IN THE NEONATAL RAT OVARY DURING FOLLICLE FORMATION

Protein distribution and mRNA expression of basement membrane collagen (type IV) during follicle formation were studied using serial section s from 24, 48 and 72 hrs. old rat ovaries. Collagen type IV, a protein found only in the basal lamina of the basement membrane, was localize d under light microscope using a polyclonal antibody. During the first 24 hrs. postpartum, immunostaining was found as thin septa separating the clusters from the stroma. By 72 hrs. postpartum, immunostaining w as found around each newly formed primordial follicle. The cell types involved in collagen type IV synthesis were determined by in situ hybr idization using a biotinylated riboprobe. Before the follicles had bee n formed, the stromal cells showed intense staining while the epitheli al presumptive granulosa cells showed a pale staining. However, after a follicle had been formed, some of the granulosa cells enclosed withi n the follicular basement membrane showed strong staining for the mess age. The presumptive granulosa cells are presumed to be the progenitor s of granulosa cells. If so, these observations suggest that the expre ssion of the message coding for collagen type IV by the granulosa cell s may be a marker for commitment of the undifferentiated cell to the g ranulosa cell lineage.