Publication

Abstract : In the teleost fish, medaka (Oryzias latipes), the sex is genetically determined at the time of fertilization. The males are heterogametic with XYnbsp;chromosomenbsp;composition, while females are of XX chromosome composition. The male sexual differentiation is initiated in XY embryos of medaka by the sex-determining genenbsp;Dmy. In this study, we have cloned the gonadal soma derived factor (Gsdf) from medaka and characterized its expression pattern during the initiation of morphological testicular differentiation. Bynbsp;real-time PCR, an XY-specificnbsp;up-regulationnbsp;was detected in the expression levels ofnbsp;Gsdfnbsp;in the whole embryos of medaka at 6nbsp;days post fertilization (dpf), coincident with the initiation of testicular differentiation in the XY gonads. Whole mount and sectionnbsp;in situ hybridizationsnbsp;reaffirmed thatnbsp;Gsdfnbsp;was expressed exclusively in primordial gonads of only the genetic males at 6nbsp;dpf. Conversely, the expression ofnbsp;Gsdfnbsp;was found to be very weak in the XX gonads during embryogenesis. Importantly,nbsp;Gsdfnbsp;andnbsp;Dmynbsp;were found to be co-localized in the samesomatic cellsnbsp;in the XY gonads. When the XY embryos were treated with estradiol-17β, in order to reverse theirnbsp;phenotypicnbsp;sex, a decline was observed in the expression ofnbsp;Gsdfnbsp;in these embryos by real-time PCR.