Kanamori Akira, Kitani Ryota, Oota Atsuko, Hirano Koudai, Myosho Taijun, Kobayashi Tohru, Kawamura Kouichi, Kato Naoyuki, Ansai Satoshi, Kinoshita Masato
Division of Biological Science, Graduate School of Science, Nagoya University, Aichi 464-8602, Japan,
Division of Biological Science, Graduate School of Science, Nagoya University, Aichi 464-8602, Japan.
Zoolog Sci. 2023 Oct;40(5):348-359. doi: 10.2108/zs230050.
In most vertebrates, the oviducts and sperm ducts are derived from the Müllerian ducts and Wolffian ducts, respectively. However, in teleosts, the genital ducts are formed by the posterior extension of gonads in both sexes. Whether the genital ducts of teleosts are newly evolved organs or variants of Müllerian ducts is an important question for understanding evolutionary mechanisms of morphogenesis. One of the genes essential for Müllerian duct formation in mice is , which is expressed in the mesenchyme and induces invagination of the coelomic epithelium and its posterior elongation. Here, we addressed the above question by examining genital duct development in mutants of two Wnt4 genes in the medaka ( is orthologous to mouse , and is paralogous). The mutants had a short body but were fertile with normal genital ducts. In contrast, both male and female mutants had their posterior elongation of the gonads stopped within or just outside the coelom. The mutants retained the posterior parts of ovarian cavities or sperm duct primordia, which are potential target tissues of Wnt4a. The gonads of female mutants (unable to synthesize sex steroids) lacked these tissues and did not develop genital ducts. Medaka was expressed in the mesenchyme ventral to the genital ducts in both sexes. Taken together, the data strongly suggest that the mouse Müllerian ducts and the medaka genital ducts share homologous developmental processes. Additionally, the or single mutants and the double mutants did not show sex-reversal, implying that both genes are dispensable for gonadal sex differentiation in the medaka.
在大多数脊椎动物中，输卵管和输精管分别源自苗勒氏管和沃尔夫氏管。然而，在硬骨鱼中，两性的生殖管道均由性腺向后延伸形成。硬骨鱼的生殖管道是新进化出的器官还是苗勒氏管的变体，这是理解形态发生进化机制的一个重要问题。小鼠中苗勒氏管形成所必需的基因之一是 ，它在间充质中表达，并诱导体腔上皮内陷及其向后延伸。在这里，我们通过研究青鳉两个Wnt4基因（ 与小鼠 直系同源， 是旁系同源）突变体中的生殖管道发育来解决上述问题。 突变体身体短小，但生殖管道正常且可育。相比之下，雄性和雌性 突变体性腺的向后延伸均在体腔内或刚超出体腔时停止。 突变体保留了卵巢腔或输精管原基的后部，这些是Wnt4a的潜在靶组织。雌性 突变体（无法合成性类固醇）的性腺缺乏这些组织，且未发育出生殖管道。青鳉 的表达存在于两性生殖管道腹侧的间充质中。综上所述，这些数据有力地表明小鼠的苗勒氏管和青鳉的生殖管道具有同源的发育过程。此外， 或 单突变体以及双突变体均未出现性反转，这意味着这两个基因对于青鳉性腺的性别分化并非必需。
