Modeling Dosage-Sensitive Sex Reversal in Mice Table 7. Reducing the Wnt4 dosage partially rescues the sex reversal phenotypes of E13.5 B6 XYPOS, B6 XYAKR, B6 Wt1+/2 XYAKR, and B6 Sf1+/2 XYAKR gonads. Maternal genotype B6 Wnt4+/2 B6 Wnt4+/2 B6 Wt1+/2 B6 Sf1+/2 Paternal genotype B6 XYPOS B6 XYAKR B6 Wnt4+/2 XYAKR B6 Wnt4+/2 XYAKR doi:10.1371/journal.pgen.1002569.t007 Fetal genotype B6 Wnt4+/+ XYPOS B6 Wnt4+/2 XYPOS B6 Wnt4+/+ XYAKR B6 Wnt4+/2 XYAKR B6 Wt1+/2; Wnt4+/+ XYAKR B6 Wt1+/2; Wnt4+/2 XYAKR B6 Sf1+/2; Wnt4+/+ XYAKR B6 Sf1+/2; Wnt4+/2 XYAKR E13.5 XY gonad phenotype Ovaries 5 (42%) 7 (25%) 0 (0%) 0 (0%) 3 (25%) 0 (0%) 8 (100%) 2 (17%) Ovotestes 7 (58%) 17 (61%) 12 (75%) 6 (33%) 5 (42%) 1 (17%) 0 (0%) 3 (25%) Testes 0 (0%) 4 (14%) 4 (25%) 12 (67%) 4 (33%) 5 (83%) 0 (0%) 7 (58%) Total gonads 12 28 16 18 12 6 8 12 transgenic XX ovotestes regress via apoptosis [51] and our preliminary analyses suggest that there is an increased number of apoptotic cells within the ovarian regions in B6 XYAKR ovotestes (data not shown). In these regions it was clear that most cells expressed either ovarian (FOXL2) or testicular (AMH) markers and that these cells could be interspersed. We propose that co-expression of ovarian and testicular markers in E13.5 B6 XY ovotestes suggests that antagonism between these opposing differentiation pathways is reduced in these XY gonads. Contrary to results reported by Bradford and colleagues [52], we did observe a few cells at the boundaries between testicular and ovarian domains that appeared to express both granulosa and Sertoli cell markers. We could not unequivocally demonstrate co-expression using the markers and techniques presented here, however, the possibility that cells expressing both female and male supporting cell progenitor markers might be present during fetal gonad differentiation warrants further investigation. Figure 6. Reduced Wnt4 dosage partially rescued cord differentiation in B6 XY genotypes that typically develop ovarian tissue. Representative images are shown for Wt1+/2 (A and B) and Sf1+/2 (C and D) B6 XYAKR E13.5 gonads that were either Wnt4+/+ (A and C) or Wnt4+/2 (B and D). The amount of tissue expressing the Sertoli cell marker AMH (green) was consistently greater in Wnt4+/2 vs. Wnt4+/+ gonads for all four sex reversals examined. Germ and vascular endothelial cells are labeled by PECAM staining (red). doi:10.1371/journal.pgen.1002569.g006 PLoS Genetics | www.plosgenetics.org 15 April 2012 | Volume 8 | Issue 4 | e1002569