Effect of FSH treatment on sheep ovary surface epithelium (OSE) smears. ( A, a ) Freshly prepared sheep OSE smear after H & E staining. Epithelial cells (spindle shaped cells with pale nuclei and abundant cytoplasm) and distinct populations of putative stem cells including the VSELs (arrow) and OGSCs (asterisk) are evident along with red blood cells (RBCs) ( B, b ) Note the increase in number of stem cells and germ cell ‘cysts’ after 15 hrs of FSH treatment. The nests represent rapid stem cells clonal expansion with incomplete cytokinesis and characteristic of the OGSCs ( C, c ) OSE smear after 15 hrs culture without FSH. These observations were made in more than three different experiments. Note absence of stem cells activity. Epithelial cells after 15 hrs culture ( B, b, C, c ) appear similar and relatively bigger in size compared to the epithelial cells in fresh OSE ( A, a ). Scale bar represents 20 μm.