Wild-derived XY Sex-reversal Mutants in the Medaka, Oryzias latipes

The medaka, Oryzias latipes, has an XX/XY sex-determination mechanism. A Y-linked DM domain gene, DMY, has been isolated by positional cloning as a sex-determining gene in this species. Previously, we found 23 XY sex-reversed females from 11 localities by examining the genotypic sex of wild-caught medaka. Genetic analyses revealed that all these females had Y-linked gene mutations. Here, we aimed to clarify the cause of this sex-reversal. To achieve this, we screened for mutations in the amino acid coding sequence of DMY, and examined DMY expression at 0 days after hatching (dah) using densitometric semiquantitative RT-PCR. We found that the mutants could be classified into two groups. One contained mutations in the amino acid coding sequence of DMY, while the other had reduced DMY expression at 0 dah although the DMY coding sequence was normal. For the latter, histological analyses indicated that Y^wOurY^wOur (Y^wOur, Y chromosome derived from an Oura XY female) individuals with the lowest DMY expression among the tested mutants were expected to develop into females at 0 dah. These results suggest that early testis development requires DMY expression above a threshold level. Mutants with reduced DMY expression may prove valuable for identifying DMY regulatory elements.

Key Words: DMY, Medaka (Oryzias latipes), mutant, sex-determination, wild population

This article has been cited by other articles:

				H. Otake, Y. Hayashi, S. Hamaguchi, and M. Sakaizumi The Y Chromosome That Lost the Male-Determining Function Behaves as an X Chromosome in the Medaka Fish, Oryzias latipes Genetics, August 1, 2008; 179(4): 2157 - 2162. [Abstract] [Full Text] [PDF]

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