Long-term iododeoxyuridine labelling analysis finds no evidence of ovarian germline stem cell activity in adult or ageing mice

The purpose of this study was to determine whether ovarian germline stem cells or any adult mitotic cell type contribute to the adult oocyte pool in vivo from early adult through to aging mice. Long-term thymidine analogue labelling assays using iododeoxyuridine (IdU) were performed to identify mitotic cells and their descendants by immunohistochemistry for IdU and germline markers Ddx4 and Oct4. C57BL/6 mice at 10 weeks, 5 months and 12 months old were given IdU for 21-30 days through their drinking water to label all dividing cells, followed by washout periods of 0-10 weeks. Over 60,000 ovarian somatic cells and oocytes were scored in 111 ovaries. No double labelling of IdU with germline stem cell markers was found in oocytes at any stage of maturity, in mice at any age. In contrast, IdU exposure during embryogenesis resulted in large numbers of labelled oocytes in postnatal mice, as expected. We were therefore unable to confirm mitotic activity in stem cells or any other progenitor replenishing the oocyte pool in C57BL/6 mice. There is no evidence that quiescent stem cells are activated when the oocyte pool is depleted by age.