Department of Medicine, Biomedical Genetics, Boston University School of Medicine, Boston, Massachusetts, USA.
PLoS Genet. 2012;8(4):e1002569. doi: 10.1371/journal.pgen.1002569. Epub 2012 Apr 5.
Sex reversal can occur in XY humans with only a single functional WT1 or SF1 allele or a duplication of the chromosome region containing WNT4. In contrast, XY mice with only a single functional Wt1, Sf1, or Wnt4 allele, or mice that over-express Wnt4 from a transgene, reportedly are not sex-reversed. Because genetic background plays a critical role in testis differentiation, particularly in C57BL/6J (B6) mice, we tested the hypothesis that Wt1, Sf1, and Wnt4 are dosage sensitive in B6 XY mice. We found that reduced Wt1 or Sf1 dosage in B6 XY(B6) mice impaired testis differentiation, but no ovarian tissue developed. If, however, a Y(AKR) chromosome replaced the Y(B6) chromosome, these otherwise genetically identical B6 XY mice developed ovarian tissue. In contrast, reduced Wnt4 dosage increased the amount of testicular tissue present in Sf1+/- B6 XY(AKR), Wt1+/- B6 XY(AKR), B6 XY(POS), and B6 XY(AKR) fetuses. We propose that Wt1(B6) and Sf1(B6) are hypomorphic alleles of testis-determining pathway genes and that Wnt4(B6) is a hypermorphic allele of an ovary-determining pathway gene. The latter hypothesis is supported by the finding that expression of Wnt4 and four other genes in the ovary-determining pathway are elevated in normal B6 XX E12.5 ovaries. We propose that B6 mice are sensitive to XY sex reversal, at least in part, because they carry Wt1(B6) and/or Sf1(B6) alleles that compromise testis differentiation and a Wnt4(B6) allele that promotes ovary differentiation and thereby antagonizes testis differentiation. Addition of a "weak" Sry allele, such as the one on the Y(POS) chromosome, to the sensitized B6 background results in inappropriate development of ovarian tissue. We conclude that Wt1, Sf1, and Wnt4 are dosage-sensitive in mice, this dosage-sensitivity is genetic background-dependant, and the mouse strains described here are good models for the investigation of human dosage-sensitive XY sex reversal.
性反转可发生在仅具有一个功能正常的 WT1 或 SF1 等位基因或包含 WNT4 的染色体区域重复的 XY 人类中。相比之下，仅具有一个功能正常的 Wt1、Sf1 或 Wnt4 等位基因的 XY 小鼠，或从转基因过表达 Wnt4 的小鼠，据报道并未发生性反转。由于遗传背景在睾丸分化中起着关键作用，特别是在 C57BL/6J（B6）小鼠中，我们测试了以下假设：在 B6 XY 小鼠中，Wt1、Sf1 和 Wnt4 是剂量敏感的。我们发现，B6 XY(B6) 小鼠中 Wt1 或 Sf1 剂量减少会损害睾丸分化，但不会形成卵巢组织。然而，如果用 Y(AKR) 染色体取代 Y(B6) 染色体，则这些在遗传上完全相同的 B6 XY 小鼠会形成卵巢组织。相比之下，减少 Wnt4 剂量会增加 Sf1+/-B6 XY(AKR)、Wt1+/-B6 XY(AKR)、B6 XY(POS) 和 B6 XY(AKR) 胎鼠中睾丸组织的数量。我们提出，Wt1(B6) 和 Sf1(B6) 是睾丸决定途径基因的功能减退等位基因，而 Wnt4(B6) 是卵巢决定途径基因的功能亢进等位基因。这一假设得到了以下发现的支持：在正常的 B6 XX E12.5 卵巢中，卵巢决定途径中的 Wnt4 和其他四个基因的表达升高。我们提出，B6 小鼠对 XY 性反转敏感，至少部分原因是它们携带了会损害睾丸分化的 Wt1(B6) 和/或 Sf1(B6) 等位基因，以及促进卵巢分化从而拮抗睾丸分化的 Wnt4(B6) 等位基因。在敏感的 B6 背景下添加一个“弱”Sry 等位基因，例如 Y(POS) 染色体上的等位基因，会导致卵巢组织的不当发育。我们得出结论，在小鼠中，Wt1、Sf1 和 Wnt4 是剂量敏感的，这种剂量敏感性依赖于遗传背景，并且这里描述的小鼠品系是研究人类剂量敏感的 XY 性反转的良好模型。
