Reproduction Abstracts (2014) 1 P024 | DOI: 10.1530/repabs.1.P024

Identification of the gene for germline sex determination in medaka

Toshiya Nishimura1,2, Tetsuya Sato3,4, Yasuhiro Yamamoto1, Ikuko Watakabe1, Yasuyuki Ohkawa4,5, Mikita Suyama3,4 & Minoru Tanaka1,2

1Laboratory of Molecular Genetics for Reproduction, National Institute for Basic Biology, Okazaki, Japan; 2The Graduate University for Advanced Studies (SOKENDAI), Okazaki, Japan; 3Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan; 4JST-CREST, Fukuoka, Japan; 5Department of Advanced Medical Initiatives, Faculty of Medicine, Kyushu University, Fukuoka, Japan.

Introduction: Sex determination is an essential process for the production of dimorphic gametes, sperms and eggs. The sex determination genes in gonadal somatic cells have been well studied, but nothing is known about the mechanism of germline sex determination in vertebrates. We have tackled a totally unaddressed issue using medaka.

Materials and methods: Using transgenic medaka in which germ cells were labeled with EGFP, three different types of germ cells, stem-type, cystic, and meiotic germ cells, were isolated by flowcytometry, followed by RNA-Seq analysis. The expression of candidate genes was screened by in situ hybridization, and the functional analysis was performed.

Results and discussion: We identified an oocyte–sperm switch gene, which was initially expressed in germ cells of indifferent gonad in both XX and XY embryos but totally disappeared during male development. The loss-of-function of homozygous XX mutants produced sperms instead of oocytes during the sex differentiation. These results suggest that germline sex determination occurs by repressing the spermatogenesis. This is the first report of the mechanism of germline sex determination in vertebrates and provides an important insight into the sex determination processes between germ cells and somatic cells.

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