In placenta mammals, a sex is genetically directed by inheritance of sex chromosomes at the time of fertilization. If the sex chromosome constitution is XX, the fertilized egg develops into a female, whereas if the constitution is XY, it becomes a male. Sex determination is actually carried out by the SRY (sex-determining region on Y) gene located on the Y chromosome. The expression starts in supporting cell precursors derived from coelomic epithelium and induces SOX9 (SRY-box 9) expression. The genus Tokudaia, Muridae, Rodentia does not adopt this sex-determining mechanism that is strictly conserved in mammals. Tokudaia consists of three species. Remarkably, two species, Tokudaia osimensis (Amami spiny rat) and Tokudaia tokunoshimensis (Tokunoshima spiny rat) have XO/XO sex chromosome constitution caused by lacking the Y chromosome. The SRY gene is also absent in these species. By contrast, the remaining one, Tokudaia muenninki (Okinawa spiny rat) has XX/XY sex chromosome constitution same as general mammals. However, their sex chromosomes have acquired the neo-X and neo-Y regions due to a fusion of a pair of autosomes to the X and Y chromosomes. Excessive duplicated copies of SRY are distributed on the Y chromosome, whereas, our previous studies indicated these were not functional. Tokudaia therefore have acquired a unique sex-determining mechanism independent of SRY. All species inhabit the southernmost islands in Japan. All are on the verge of extinction and successful artificial breeding has not been achieved, hence, we have studied Tokudaia using limited materials. In this session, I will show recent data of the unique sex chromosome evolution and the sex-determining mechanism in Tokudaia.
In placenta mammals, a sex is genetically directed by inheritance of sex chromosomes at the time of fertilization. If the sex chromosome constitution is XX, the fertilized egg develops into a female, whereas if the constitution is XY, it becomes a male. Sex determination is actually carried out by the SRY (sex-determining region on Y) gene located on the Y chromosome. The expression starts in supporting cell precursors derived from coelomic epithelium and induces SOX9 (SRY-box 9) expression. The genus Tokudaia, Muridae, Rodentia does not adopt this sex-determining mechanism that is strictly conserved in mammals. Tokudaia consists of three species. Remarkably, two species, Tokudaia osimensis (Amami spiny rat) and Tokudaia tokunoshimensis (Tokunoshima spiny rat) have XO/XO sex chromosome constitution caused by lacking the Y chromosome. The SRY gene is also absent in these species. By contrast, the remaining one, Tokudaia muenninki (Okinawa spiny rat) has XX/XY sex chromosome constitution same as general mammals. However, their sex chromosomes have acquired the neo-X and neo-Y regions due to a fusion of a pair of autosomes to the X and Y chromosomes. Excessive duplicated copies of SRY are distributed on the Y chromosome, whereas, our previous studies indicated these were not functional. Tokudaia therefore have acquired a unique sex-determining mechanism independent of SRY. All species inhabit the southernmost islands in Japan. All are on the verge of extinction and successful artificial breeding has not been achieved, hence, we have studied Tokudaia using limited materials. In this session, I will show recent data of the unique sex chromosome evolution and the sex-determining mechanism in Tokudaia.
2B9 - Building 2 GSA2018_APCC6 GSACC62018@canberra.edu.au
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