Molecular assessment, characterization, and differentiation of theca stem cells imply the presence of mesenchymal and pluripotent stem cells in sheep ovarian theca layer.

The ability of ovarian theca stem cells to differentiate into oocyte and theca cells may lead to a major advancement in reproductive biology and infertility treatments. However, there is little information about function, growth and differentiation potential of these immature cells. In this study adult sheep theca stem cells (TSCs) characteristics, and differentiation potential into osteocyte-like cells (OSLCs), adipocyte-like cells (ALCs), theca progenitor-like cells (TPCs), and oocyte-like cells (OLCs) were investigated. TSCs were isolated, cultured, and compared with mesenchymal stem cells (MSCs), fibroblast cells (FCs), and pluripotent embryonic ovarian cells (EO). Adherent TSCs were morphologically similar to FCs. Cell cycle analysis showed high proliferation capacity of TSCs. TSCs were positive for the mesenchymal cells surface markers, and also expressed POU5F1. Differentiation potential of TSCs into OSLCs and ALCs were confirmed by alizarin red and oil red staining respectively. OSTEOCALCIN and COL1 were expressed in OSLCs. ALCs were positive for PPARα and LPL. TPCs expressed theca specific genes (GLI2, GLI3, PTCH1, CYP17A1, 3β-HSD and LHR) and secreted testosterone, dehydroepiandrostenedione (DHEA), androstenedione, progesterone and estradiol. Lipid droplets in these steroid cells were viewed by oil red staining. OLCs expressed oocyte-specific marker genes including, ZP3, ZP2, GDF9, SYCP3, PRDM1, STELLA, FRAGILIS, DAZL, as well as POU5F1, and showed separated sphere structure. Our results indicated that TSCs derived from ovarian follicles contain MSCs and pluripotent stem cells (PSCs) that can be differentiated into lineages of mesenchymal origin and are capable of differentiation into TPCs and OLCs under in vitro conditions.