Ovarian stem cells: absence of evidence is not evidence of absence

Deepa Bhartiya, Kalpana Sriraman, Seema Parte, Hiren Patel

Lei and Spradling in a recent study published in PNAS failed to detect 'germline cysts' by elegant studies using lineage tracing approach and thus concluded that adult mouse ovaries lack stem cells. They proposed that primordial follicle pool generated during fetal life is sufficient to sustain oogenesis and that there is no renewal of oocytes during adult life. Contrary to their results, we have reported presence of very small pluripotent, embryonic-like stem cells (VSELs), their immediate descendants (OGSCs) and germ cell 'cysts' or 'nests' (formed by rapid cell division and incomplete cytokinesis) in surface epithelial cell smears of adult sheep, monkey and human ovaries.