Abstract
BackgroundLei 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.MethodsIn the present study, ovaries were collected from adult mouse (treated with 5 IU pregnant mare serum gonadotropin, PMSG) and sheep (from slaughter house) and testis from mouse treated with busulphan (25 mg/Kg). Ovarian surface epithelial (OSE) cells and testicular smears were studied for the presence of cysts. Sheep OSE smears were also used to show cytoplasmic continuity amongst the cyst cells studied by immunolocalization and confocal microscopy of stem cells specific markers OCT-4 and SSEA-4.ResultsCysts were observed and confocal microscopy imaging confirmed cytoplasmic continuity amongst the cells comprising the cysts.ConclusionsCysts represent self-renewal and clonal expansion of stem cells with incomplete cytokinesis and are a hallmark feature of stem cells. We suggest the use of PMSG stimulated mouse ovaries and use of more primitive markers like OCT-4 or STELLA rather than MVH for lineage tracing studies to conclusively show presence of stem cells by lineage-tracing studies.
Highlights
Sphere forming ability is considered a hallmark property of stem cells including cancer stem cells
Compelling evidence has been provided by several groups in support of postnatal oogenesis, the subject has been challenged and negated by many including Lei & Spradling [1] who found no evidence of stem cells in mouse ovary using genetic recombination approach
We have published several papers on gonadal VSELs [7,8,9,10,12,13,14] and have shown that similar to the VSELs in the bone marrow and cord blood [15,16], the VSELs in gonads are spherical cells, smaller than red blood cells, with high nucleo-cytoplasmic ratio, stain very dark with Haematoxylin, do not stain with DAPI, express pluripotent (OCT-4A, SSEA-4, Nanog, Sox-2, Rex), primordial germ cells (STELLA, FRAGILIS), VSELs (SCA-1, CD133) and germ cells (VASA, DAZL) specific markers. They are located in the ovary surface epithelium and in the basal epithelium of testicular seminiferous tubules. They are quiescent in nature and self-renew to give rise to the progenitors which divide rapidly with incomplete cytokinesis and occasionally appear as cysts and differentiate further and undergo meiosis to give rise to the gametes
Summary
Ovaries were collected from adult mouse (treated with 5 IU pregnant mare serum gonadotropin, PMSG) and sheep (from slaughter house) and testis from mouse treated with busulphan (25 mg/Kg). Ovarian surface epithelial (OSE) cells and testicular smears were studied for the presence of cysts. Sheep OSE smears were used to show cytoplasmic continuity amongst the cyst cells studied by immunolocalization and confocal microscopy of stem cells specific markers OCT-4 and SSEA-4
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