Kanamori Akira, Kobayashi Yasuhisa
Group of Development and Growth Regulation, Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Japan.
Laboratory for Aquatic Biology, Department of Fisheries, Faculty of Agriculture, Kindai University, Nara, Japan.
Front Cell Dev Biol. 2023 Dec 22;11:1328024. doi: 10.3389/fcell.2023.1328024. eCollection 2023.
Mature gametes are transported externally for fertilization. In vertebrates, the gonads are located within the coelom. Consequently, each species has specific organs for export, which often vary according to sex. In most vertebrates, sperm ducts and oviducts develop from the Wolffian and Müllerian ducts, respectively. However, exceptions exist. Both sexes of cyclostomes, as well as females of basal teleosts, lack genital ducts but possess genital pores. In teleosts of both sexes, genital ducts are formed through the posterior extensions of gonads. These structures appear to be independent of both Wolffian and Müllerian ducts. Furthermore, the development of Wolffian and Müllerian ducts differs significantly among various vertebrates. Are these gamete-exporting organs homologous or not? A question extensively debated around the turn of the 20th century but now largely overlooked. Recent research has revealed the indispensable role of Wnt4a in genital duct development in both sexes of teleosts: zebrafish and medaka. is an ortholog of mammalian , which has functions in Müllerian duct formation. These results suggest a potential homology between the mammalian Müllerian ducts and genital ducts in teleosts. To investigate the homology of gamete-exporting organs in vertebrates, more detailed descriptions of their development across vertebrates, using modern cellular and genetic tools, are needed. Therefore, this review summarizes existing knowledge and unresolved questions on the structure and development of gamete-exporting organs in diverse vertebrate groups. This also underscores the need for comprehensive studies, particularly on cyclostomes, cartilaginous fishes, basal ray-finned fishes, and teleosts.
成熟的配子被运输到体外进行受精。在脊椎动物中，性腺位于体腔内。因此，每个物种都有特定的输出器官，这些器官通常因性别而异。在大多数脊椎动物中，输精管和输卵管分别由中肾管和缪勒氏管发育而来。然而，也有例外情况。圆口纲动物的两性以及基干硬骨鱼的雌性都没有生殖管道，但有生殖孔。在硬骨鱼的两性中，生殖管道是通过性腺的后部延伸形成的。这些结构似乎独立于中肾管和缪勒氏管。此外，中肾管和缪勒氏管在不同脊椎动物中的发育差异很大。这些配子输出器官是否同源呢？这是一个在20世纪之交广泛争论但现在基本被忽视的问题。最近的研究揭示了Wnt4a在硬骨鱼（斑马鱼和青鳉）两性生殖管道发育中的不可或缺的作用。它是哺乳动物[此处原文缺失相关基因名称]的直系同源基因，在缪勒氏管形成中发挥作用。这些结果表明哺乳动物的缪勒氏管与硬骨鱼的生殖管道之间可能存在同源性。为了研究脊椎动物配子输出器官的同源性，需要使用现代细胞和遗传工具对它们在整个脊椎动物中的发育进行更详细的描述。因此，本综述总结了关于不同脊椎动物类群中配子输出器官的结构和发育的现有知识以及未解决的问题。这也强调了进行全面研究的必要性，特别是对圆口纲动物、软骨鱼、基干辐鳍鱼和硬骨鱼的研究。
