Yoshimoto Shin, Okada Ema, Umemoto Hirohito, Tamura Kei, Uno Yoshinobu, Nishida-Umehara Chizuko, Matsuda Yoichi, Takamatsu Nobuhiko, Shiba Tadayoshi, Ito Michihiko
Department of Bioscience, School of Science, Kitasato University, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan.
Proc Natl Acad Sci U S A. 2008 Feb 19;105(7):2469-74. doi: 10.1073/pnas.0712244105. Epub 2008 Feb 11.
In the XX/XY sex-determining system, the Y-linked SRY genes of most mammals and the DMY/Dmrt1bY genes of the teleost fish medaka have been characterized as sex-determining genes that trigger formation of the testis. However, the molecular mechanism of the ZZ/ZW-type system in vertebrates, including the clawed frog Xenopus laevis, is unknown. Here, we isolated an X. laevis female genome-specific DM-domain gene, DM-W, and obtained molecular evidence of a W-chromosome in this species. The DNA-binding domain of DM-W showed a strikingly high identity (89%) with that of DMRT1, but it had no significant sequence similarity with the transactivation domain of DMRT1. In nonmammalian vertebrates, DMRT1 expression is connected to testis formation. We found DMRT1 or DM-W to be expressed exclusively in the primordial gonads of both ZZ and ZW or ZW tadpoles, respectively. Although DMRT1 showed continued expression after sex determination, DM-W was expressed transiently during sex determination. Interestingly, DM-W mRNA was more abundant than DMRT1 mRNA in the primordial gonads of ZW tadpoles early in sex determination. To assess the role of DM-W, we produced transgenic tadpoles carrying a DM-W expression vector driven by approximately 3 kb of the 5'-flanking sequence of DM-W or by the cytomegalovirus promoter. Importantly, some developing gonads of ZZ transgenic tadpoles showed ovarian cavities and primary oocytes with both drivers, suggesting that DM-W is crucial for primary ovary formation. Taken together, these results suggest that DM-W is a likely sex (ovary)-determining gene in X. laevis.
在XX/XY性别决定系统中，大多数哺乳动物的Y连锁SRY基因以及硬骨鱼青鳉的DMY/Dmrt1bY基因已被确定为触发睾丸形成的性别决定基因。然而，包括非洲爪蟾在内的脊椎动物的ZZ/ZW型系统的分子机制尚不清楚。在此，我们分离出了非洲爪蟾雌性基因组特异性的DM结构域基因DM-W，并获得了该物种存在W染色体的分子证据。DM-W的DNA结合结构域与DMRT1的DNA结合结构域具有极高的同源性（89%），但与DMRT1的反式激活结构域没有明显的序列相似性。在非哺乳动物脊椎动物中，DMRT1的表达与睾丸形成相关。我们发现DMRT1或DM-W分别仅在ZZ和ZW或ZW蝌蚪的原始性腺中表达。尽管DMRT1在性别决定后持续表达，但DM-W仅在性别决定期间短暂表达。有趣的是，在性别决定早期，ZW蝌蚪原始性腺中DM-W mRNA的丰度高于DMRT1 mRNA。为了评估DM-W的作用，我们构建了携带由约3 kb的DM-W 5'侧翼序列或巨细胞病毒启动子驱动的DM-W表达载体的转基因蝌蚪。重要的是，两种驱动方式下，一些ZZ转基因蝌蚪发育中的性腺都出现了卵巢腔和初级卵母细胞，这表明DM-W对初级卵巢的形成至关重要。综上所述，这些结果表明DM-W可能是非洲爪蟾的性别（卵巢）决定基因。
