Immunolocalization of FSH receptors on sheep ovarian sections (i) FSH receptors. ( A ) Ovary surface epithelial cells and primordial follicles showing positive staining for FSHR ( B ) Primordial follicles (asterix) exhibit positive FSHR staining in the oocyte nucleus as well as in the ooplasm whereas the surrounding granulosa cells are negative for FSHR (arrow) ( C ) Secondary follicle showing positive staining for FSHR in oocyte nucleus and ooplasm and negative for surrounding granulosa cells ( D &E ) Developing antral follicles show FSHR positive in both ooplasm and surrounding granulosa cells. (ii) OCT-4 ( A &B ) certain regions of ovary surface epithelium stain positive for OCT-4. Primordial follicles exhibit positive OCT-4 staining in the ooplasm (arrow) as well as in the nuclei (asterix) of the oocytes. The secondary follicles show distinct staining in the ooplasm whereas the surrounding granulosa cells in both primordial and secondary follicles are negative for OCT-4. ( C &D ) Large antral follicles have distinct staining for OCT-4 in the granulosa cells whereas the theca cells are negative and note a gradient in the staining intensity at higher magnification. Scale bar is 20 μm. Images of representative area were photographed using 90i Nikon microscope.