Endocrine Abstracts

The origins and lineages of somatic cells in mammalian ovaries are poorly understood and not universally agreed upon. By clonally-isolating different phenotypes of bovine fetal stromal cells and conducting microarray analysis, we identified markers of different somatic cells. Antibodies to these markers, markers of other known cell types in fetal ovaries and to extracellular matrix were used to examine bovine ovaries (60–300 days of gestation, n=51) by immunohistochemistry. We show that the gonadal ridge is initially formed by replication of surface epithelium of the mesonephros giving rise to a cluster of cells expressing only some epithelial markers (abbreviated to gonadal ridge epithelial like (GREL) cells). Primordial germ cells migrate into the gonadal ridge and form oogonia and replicate. Stroma from the mesonephros also penetrates into the gonadal ridge forming alternating areas of stroma and irregularly shaped ovigerous cords, composed of oogonia and GREL cells. The stroma brings with it capillaries from the mesonephros. Importantly the stroma is always continuously surrounded by a basal lamina, separating it initially from the ovigerous cords. Stromal cells also migrate to just under the outer layers of GREL cells on the surface and spread laterally, establishing a basal lamina under the cells on the ovarian surface and an epithelial/stromal interface and hence a mature ovarian surface epithelium. Stroma continues to partition the ovigerous cords, still with a basal lamina at the interface, to form follicles containing an oogonium/oocyte and GREL cells that form the granulosa cells. This region is the ovarian cortex. The ovarian medulla below is largely residual mesonephric stroma containing some rete ovarii derived from mesonephric nephrons. In summary we have identified the cell lineages and the cell fate decisions needed for maturation of all the different somatic cells in the adult ovary.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.