Table 6. Strain distribution pattern of the Sf1A172 versus Sf1S172 alleles. Inbred strain F1 phenotype NcoI genotype rs3142929 confirmed C57BL/6J C57BL/10J NZB/BlNJ DBA/2J 129S1/SvImJ C3H/HeSnJ SM/J C58/J BALB/cBy B6-like B6-like B6-like D2-like D2-like D2-like D2-like D2-like D2-like + + 2 2 2 2 2 2 + 2* + + + + + +* + not available *Indicates an imputed value. doi:10.1371/journal.pgen.1002569.t006 contrast, Wnt4 expression was elevated in Wt1+/2 and Sf1+/2 B6 XYAKR gonads compared to +/+ gonads, but we suspect that this increase is due to the presence of more ovarian tissue in these gonads. Expression of Wnt4 also was reduced in Wt1+/2 XX and XY mesonephroi. Because Sf1 is not expressed in mesonephroi, reduced Wnt4 expression indicates in this tissue WT1 regulates Modeling Dosage-Sensitive Sex Reversal in Mice Wnt4 expression independently of SF1. Ptch1 expression also was reduced in Wt1+/2 XX and XY mesonephroi. Interestingly, Ptch1 is strongly expressed in the region where the mesonephric tubules form and the number of tubules is reduced in Wt12/2 mesonephroi [14]. This result suggests that Wt1 regulates Ptch1 expression and that Ptch1 could have a role in the formation of mesonephric tubules. However, these WISH results, though quite intriguing, require confirmation with a more quantitative method such as qRT-PCR. Co-expression of ovarian and testicular markers suggests reduced antagonism of the ovary and testis differentiation pathways in B6 XY gonads Analysis of E13.5 B6 XYAKR gonads showed that the anterior and posterior regions that lacked testicular cords expressed multiple ovarian somatic cell markers and that the germ cells within these domains had initiated meiosis. Therefore, these regions were not simply undifferentiated, but rather had initiated the ovary differentiation program in both somatic and germ cells. By E15.5, testicular cords are present throughout B6 XYAKR gonads and it is unclear what happens to the ovarian regions between these two stages. Two possibilities are that these ovarian cells might transdifferentiate into the analogous testicular cell types, or regress via apoptosis. A recent analysis showed that the ovarian regions in Sox9 Figure 5. Wt1 but not Sf1 transcript levels were significantly lower in B6 versus D2 gonad/mesonephros complexes. Real-time qRT-PCR analysis of Wt1 and Sf1 expression normalized to Gapdh (22DCt) showing mean transcript levels +/2 standard error. Wt1 and Sf1 expression were determined in the same B6 and D2 samples, therefore the samples sizes are only shown above the corresponding error bars for the Wt1B6 and Wt1D2 comparisons. An asterisk denotes statistically significant differences in pairwise comparisons (a = 0.05). Wt1 expression was significantly lower in B6 vs. D2 samples at E10.5 (10–13 ts, t15 = 2.063, p,0.0284), E11.0 (14–17 ts, t40 = 5.355, p,0.00002), E11.5 (18–21 ts, t29 = 1.699, p,0.0500), E12.5 (27– 30 ts, t10 = 3.441, p,0.0032), and E13.5 (t12 = 5.985, p,0.0003). Wt1 expression also was lower in B6 than in D2 samples at E12.0 (27–30 ts) but the difference did not reach statistical significance (t13 = 1.741, p,0.0526). Sf1 expression was lower in B6 vs. D2 gonad/mesonephros complexes at E11.0 (t40 = 1.466, p,0.0753), E11.5 (t29 = 1.182, p,0.1235), and E12.0 (t13 = 1.208, p,0.1243), but these differences were not statistically significant. doi:10.1371/journal.pgen.1002569.g005 PLoS Genetics | www.plosgenetics.org 14 April 2012 | Volume 8 | Issue 4 | e1002569