Oshima Yuki, Noguchi Koki, Nakamura Masahisa
Department of Biology, Faculty of Education and Integrated Arts and Sciences, Waseda University, Shinjuku-ku, Tokyo 169-8050, Japan.
Zoolog Sci. 2007 Aug;24(8):798-802. doi: 10.2108/zsj.24.798.
Lhx9 is a LIM-homeodomain (HD) transcription factor. Transcripts of the Lhx9 gene are present in the urogenital ridges of mouse embryos. In Lhx9-deficient mice, a discrete gonad is not formed (Birk et al., 2000). To date, however, the role of Lhx9 in gonad formation has not been studied in animals other than chicks and mice. Thus, this study was aimed at determining whether or not Lhx9 is expressed in the developing gonads of amphibians. We first isolated cDNAs of Lhx9 and four isoforms, named Lhx9alpha, beta, gamma and delta, from the frog Rana rugosa. All the isoforms lacked the last 14 amino acids of the HD (the DNA-binding motif). RT-PCR analysis revealed that Lhx9 and Lhx9alpha were highly expressed in the ovary, testis, brain and heart of adult frogs. However, neither Lhx9 nor any of the four isoforms was expressed in the pancreas and kidney. When their expression in the developing gonads of R. rugosa was examined by RT-PCR, transcripts of Lhx9 and Lhx9alpha were detected with no sexual dimorphism during sex determination. Lhx9gamma and Lhx9delta were also expressed, but at a low level. In contrast, the Lhx9beta transcript was hardly detected. In addition, in situ hybridization analysis showed that R. rugosa Lhx9 was expressed in somatic cells in the developing gonad and mesonephros far before sex determination. Taken together, Lhx9 and its four isoforms are probably involved in organogenesis in R. rugosa. All the isoforms may function as an endogenous dominant-negative form of Lhx9 in this species.
Lhx9是一种含LIM结构域的同源异型框（HD）转录因子。Lhx9基因的转录本存在于小鼠胚胎的泌尿生殖嵴中。在Lhx9基因缺陷的小鼠中，无法形成离散的性腺（伯克等人，2000年）。然而，迄今为止，除了鸡和小鼠之外，尚未在其他动物中研究Lhx9在性腺形成中的作用。因此，本研究旨在确定Lhx9是否在两栖动物发育中的性腺中表达。我们首先从小皱蛙中分离出Lhx9及其四种同工型的cDNA，分别命名为Lhx9α、β、γ和δ。所有同工型均缺少HD（DNA结合基序）的最后14个氨基酸。逆转录聚合酶链反应（RT-PCR）分析显示，Lhx9和Lhx9α在成年青蛙的卵巢、睾丸、脑和心脏中高表达。然而，Lhx9及其四种同工型在胰腺和肾脏中均未表达。当通过RT-PCR检测它们在小皱蛙发育中性腺中的表达时，在性别决定期间未检测到Lhx9和Lhx9α转录本的性二态性。Lhx9γ和Lhx9δ也有表达，但水平较低。相比之下，几乎检测不到Lhx9β转录本。此外，原位杂交分析表明，在性别决定之前很久，小皱蛙Lhx9就在发育中的性腺和中肾的体细胞中表达。综上所述，Lhx9及其四种同工型可能参与了小皱蛙的器官发生。在该物种中，所有同工型可能作为Lhx9的内源性显性负性形式发挥作用。
