Stem Cells in Adult Mice Ovaries Form Germ Cell Nests, Undergo Meiosis, Neo-oogenesis and Follicle Assembly on Regular Basis During Estrus Cycle

Very small embryonic-like (VSELs) and ovarian (OSCs) stem cells are located in adult mammalian ovary surface epithelium (OSE). OSCs can expand long-term and differentiate into oocyte-like structures in vitro and have resulted in birth of fertile pups. Lineage tracing studies have provided evidence t...

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Bibliographic Details
Published in:Stem cell reviews and reports 2021-10, Vol.17 (5), p.1695-1711
Main Authors: Sharma, Diksha, Bhartiya, Deepa
Format: Article
Language:English
Subjects:
Animals
Apoptosis
Biomedical and Life Sciences
Biomedical Engineering and Bioengineering
Bromodeoxyuridine
Cell Biology
Cytochrome c
Cytokinesis
Embryos
Epithelium
Estrus
Estrus cycle
Female
Fetuses
Flow cytometry
Follicles
Germ Cells
Green fluorescent protein
Life Sciences
Meiosis
Mice
Mitochondria
Mitosis
Oct-4 protein
Oocytes
Oogenesis
Ovaries
Ovary
Regenerative Medicine/Tissue Engineering
Stem cell transplantation
Stem Cells
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Summary:Very small embryonic-like (VSELs) and ovarian (OSCs) stem cells are located in adult mammalian ovary surface epithelium (OSE). OSCs can expand long-term and differentiate into oocyte-like structures in vitro and have resulted in birth of fertile pups. Lineage tracing studies have provided evidence to suggest OSCs differentiation into oocytes in vivo. But how these stem cells function under normal physiological conditions has not yet been well worked out. Besides studying STRA-8 and SCP-3 expression in enzymatically isolated OSE cells smears, mice were injected BrdU to track mitosis, meiosis and follicle assembly. H&E stained OSE cells during late diestrus and proestrus showed VSELs undergoing asymmetrical cell divisions to give rise to slightly bigger OSCs which in turn underwent symmetrical cell divisions followed by clonal expansion (rapid expansion with incomplete cytokinesis) during early estrus to form germ cell nests (GCN). OCT-4, SSEA-1, MVH and DAZL positive cells in GCN expressed Erα, Erβ and FSHR, were interconnected by ring canals (TEX-14), showed mitochondrial aggregation (Cytochrome C) and Balbiani Body (TRAL). Apoptosis in ‘nurse’ cells was marked by PARP and putative oocytes were clearly visualized. BrdU was detected in cells undergoing mitosis/meiosis and also in an oocyte of secondary follicle. FACS sorted, green fluorescent protein (GFP) positive VSELs upon transplantation resulted in GFP positive GCN suggesting crucial role for VSELs in adult ovaries. Results suggest that various events described during oogenesis and follicle assembly in fetal ovaries are recapitulated on regular basis in adult ovary and result in the formation of follicles. Graphic abstract
ISSN:2629-3269
2629-3277
DOI:10.1007/s12015-021-10237-4