Revisiting Claims of the Continued Absence of Functional Germline Stem Cells in Adult Ovaries

Characterization of Oogonial Stem Cells in Adult Mouse Ovaries with Age and Comparison to In Silico Data on Human Ovarian Aging

“…These observations once again highlight the discordance in questions raised by some scientists about the validity of COOH-Ddx4 antibody-based sorting to isolate OSCs [ 40–42 ] (see also Woods and Tilly [ 43 ], Alberico et al [ 14 ], and Woods and Tilly [ 44 ]) with what has been experimentally established, and reproduced, by multiple laboratories since 2009 (see supporting information table 1 in Alberico et al [ 14 ] for a more comprehensive listing of published studies using COOH-Ddx4 antibody-based sorting approaches to study OSCs across species). In this regard, related ongoing claims of an absence of evidence supporting the existence of functional OSCs in adult ovaries [ 42 ]—with function defined by the ability of OSCs to differentiate into new oocytes that mature into competent eggs that can be fertilized to produce embryos and viable offspring, are equally discordant with the numerous published studies that have unequivocally established the functionality of OSCs through multiple approaches (reviewed in Woods and Tilly [ 44 ]).…”

“…For example, in a carefully controlled assessment of the impact of flow cytometry on gene expression, it was found that FACS, per se, has a minimal transcriptomic effect in cells; however, the same study found that the enzymatic and mechanical disaggregation of the starting tissue into a single-cell suspension required for flow cytometry, and by inference snRNA-seq or scRNA-seq, triggers an upregulation in expression of numerous microRNAs, which in turn is associated with a decrease in expression of their predicted target genes [ 89 ]. Studies such as these underscore a major limitation of single-cell gene expression technologies: conclusions drawn about cell lineage identification or function based solely on transcriptomic changes across the samples being compared are not only rooted in correlation [ 44 , 88 ] but also can be artifactually influenced by sample preparation protocols [ 89 ].…”

“…To explore the possibility that OSCs are comprised of subpopulations that differ phenotypically and functionally, and that this heterogeneity may be important to consider in studies of how aging impacts OSC dynamics, here we characterized OSCs isolated from adult mouse ovaries by flow cytometry using antibodies to detect extracellular expression of the carboxy terminus of DEAD box helicase-4 (COOH-Ddx4) [ 3 , 4 , 39 ]. Although numerous studies have successfully sorted viable OSCs from the ovaries of diverse species using antibodies against COOH-Ddx4 [ 3 , 4 , 6–14 , 16–23 , 39 ] (see also supporting information table 1 in Alberico et al [ 14 ] for a more complete listing of relevant publications), a few scientists have continued to claim that this OSC sorting protocol is flawed [ 40–42 ] (see also Woods and Tilly [ 43 ], Alberico et al [ 14 ], and Woods and Tilly [ 44 ]).…”

mTOR Inhibition via Low-Dose, Pulsed Rapamycin with Intraovarian Condensed Platelet Cytokines: An Individualized Protocol to Recover Diminished Reserve?

“…Perhaps most crucially, stem cells near the ovarian surface epithelium [20,21] are well placed for research and clinical access. These cells display features which permit cellular transformations into different functional lineages (e.g., epithelium to mesenchyme) [22][23][24]. Local macrophages assert some role in this, although how this influence occurs is not known exactly.…”