Fig. 1

a Schematic representation of stem cells compared to fully differentiated somatic cell (not drawn to scale). Stem cells are quiescent, spherical cells of small size and with high nucleocytoplasmic ratio. When cells suspension is centrifuged, the somatic cells pellet down at 300 g (and care is taken not to spin at a higher speed in order to protect them from rupturing). However, at this speed, the stem cells remain buoyant and get unknowingly discarded. b Surface epithelial cells gently scraped from sheep ovary after Hematoxylin & Eosin staining. One can see sheets of epithelial cells and at places small, spherical, darkly stained putative stem cells. These stem cells have been characterized in details elsewhere [2, 3]