Supplementary Material for: Expression and Functional Analysis of Dkk1 during Early Gonadal Development

WNT signalling plays a central role in mammalian sex determination by promoting ovarian development and repressing aspects of testis development in the early gonad. Dickkopf homolog 1 (DKK1) is a WNT signalling antagonist that plays critical roles in multiple developmental systems by modulating WNT activity. Here, we examined the role of DKK1 in mouse sex determination and early gonadal development. <i>Dkk1</i> mRNA was upregulated sex-specifically during testis differentiation, suggesting that DKK1 could repress WNT signalling in the developing testis. However, we observed overtly normal testis development in <i>Dkk1</i>-null XY gonads, and found no significant upregulation of <i>Axin2</i> or <i>Sp5</i> that would indicate increased canonical WNT signalling. Nor did we find significant differences in expression of key markers of testis and ovarian development. We propose that DKK1 may play a protective role that is not unmasked by loss-of-function in the absence of other stressors.