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.
Mice lacking equilibrative nucleoside transporter 1 (ENT1
−/−) demonstrate progressive calcification of spinal tissues including the annulus fibrosus (AF) of the intervertebral disc (IVD). We previously established ENT1 as the primary nucleoside transporter in the AF and demonstrated dysregulation of biomineralization pathways. To identify cellular pathways altered by loss of ENT1, we conducted microarray analysis of AF tissue from wild‐type (WT) and ENT1
−/− mice before calcification (2 months of age) and associated with calcification (6 months of age). Bioinformatic analyses identified cell cycle dysregulation in ENT1
−/− AF tissues and implicated the E2f family of transcription factors as potential effectors. Quantitative polymerase chain reaction analysis confirmed increased expression of multiple E2f transcription factors and E2f interacting proteins (
Rb1 and Cdk2) in ENT1
−/− AF cells compared with WT at 6 months of age. At this time point, ENT1
−/− AF tissues showed increased JNK MAPK pathway activation, CDK1, minichromosome maintenance complex component 5 (Mcm5), and proliferating cell nuclear antigen (PCNA) protein expression, and PCNA‐positive proliferating cells compared with WT controls. The current study demonstrates that loss of ENT1‐mediated adenosine transport leads to increased cell proliferation in the AF of the IVD.
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