Abstract
BackgroundRetinoic acid (RA) signaling has been identified as a key driver in male and female gamete development. The presence of RA is a critical step in the initiation of meiosis and is required for the production of competent oocytes from primordial germ cells. Meiosis has been identified as a difficult biological process to recapitulate in vitro, when differentiating stem cells to germ cells. We have previously shown that primordial germ cell-like cells, and more advanced oocyte-like cells (OLCs), can be formed by differentiating mouse skin-derived stem cells. However, the OLCs remain unable to function due to what appears to be failure of meiotic initiation. The aim of this study was to determine the effect of RA treatment, during stem cell differentiation to germ cells, particularly on the initiation of meiosis.ResultsUsing qPCR we found significant increases in the meiosis markers Stra8 and Sycp3 and a significant reduction in the meiosis inhibitor Nanos2, in the differentiating populations. Furthermore, OLCs from the RA treated group, expressed significantly more of the meiosis regulatory gene Marf1 and the oocyte marker Oct4. At the protein level RA treatment was found to increase the expression of the gap junction protein CX43 and the pluripotency marker OCT4. Moreover, the expression of SYCP3 was significantly upregulated and the localization pattern better matched that of control fetal ovarian cells. RA treatment also improved the structural integrity of the OLCs produced by initiating the expression of all three zona pellucida transcripts (Zp1–3) and improving ZP3 expression levels and localization. Finally, the addition of RA during differentiation led to an almost two-fold increase in the number of OLCs recovered and increased their in vitro growth.ConclusionRA is a key driver in the formation of functioning gametes and its addition during stem cell to germ cell differentiation improves OLCs entry into meiosis.
Highlights
Retinoic acid (RA) signaling has been identified as a key driver in male and female gamete development
Treatment of differentiations with RA results in altered expression of meiosis markers Initially, in order to determine the induction of meiosis we compared transcript levels of the meiosis marker genes stimulated by RA 8 (Stra8) and Sycp3
We found the expression of Stra8 was significantly higher, at 11.63 ± 7.64 fold, following RA treatment (p < 0.01, Fig. 1a)
Summary
Retinoic acid (RA) signaling has been identified as a key driver in male and female gamete development. We have previously shown that primordial germ cell-like cells, and more advanced oocyte-like cells (OLCs), can be formed by differentiating mouse skin-derived stem cells. The first evidence of entry into meiosis I can be seen at ~ 13.5 days postcoitum (dpc) in the female fetal mouse [1] This decision has been shown to be influenced by the presence of retinoic acid (RA) which is produced by mesonephroi during embryogenesis in both sexes [2]. We have shown that skin-derived somatic stem cells, from pigs, mice and humans, have the ability to form primordial germ cell-like cells (PGCLCs) and non-functioning oocyte-like cells (OLCs) [16,17,18,19,20,21]. The use of ES cells is impeded by moral, legal, and ethical concerns
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