Supplementary Material for: Loss of <i>R-Spondin1</i> and <i>Foxl2</i> Amplifies Female-to-Male Sex Reversal in XX Mice

In vertebrates, 2 main genetic pathways have been shown to regulate ovarian development. Indeed, a loss of function mutations in <i>Rspo1</i> and <i>Foxl2</i> promote partial female-to-male sex reversal. In mice, it has been shown that the secreted protein RSPO1 is involved in ovarian differentiation and the transcription factor FOXL2 is required for follicular formation. Here, we analysed the potential interactions between these 2 genetic pathways and have shown that while <i>Rspo1</i> expression seems to be independent of <i>Foxl2 </i>up-regulation, <i>Foxl2</i> expression partly depends of <i>Rspo1 </i>signalisation. This suggests that different <i>Foxl2</i>-positive somatic cell lineages exist within the ovaries. In addition, a combination of both mutated genes in XX <i>Foxl2</i><sup>–/–</sup><i>/Rspo1</i><sup>–/–</sup> gonads promotes sex reversal, detectable at earlier stages than in XX <i>Rspo1</i><sup>–/–</sup> mutants. Ectopic development of the steroidogenic lineage is more pronounced in XX <i>Foxl2</i><sup>–/–</sup><i>/Rspo1</i><sup>–/–</sup> gonads than in XX <i>Rspo1</i><sup>–/–</sup> embryos, suggesting that <i>Foxl2</i> is involved in preventing ectopic steroidogenesis in foetal ovaries.