Molecular Genetics of Sex chromosomes of the medaka Oryzias latipes

利用一株日本稻属（Oryzias latipes）雄性决定因子基因菌株，筛选基因组DNA文库，分离出两个性别连锁的DNA克隆SL-5和SL-110。核苷酸序列完全确定。SL-5为单拷贝序列，大小为1.7 kb。SL-110是一个长度为498 b的重复序列。我们在这些克隆的两端设计了PCR引物。使用SL-5引物组合的PCR产物长度在两种自交系（Hd-rR和HNI）之间存在差异。使用SL-110引物的PCR产物在被Hae III消化后呈现出不同的裂解模式。利用Hd-rR和HNI回交检测了共4个位点的分离，其中包括两个DNA位点（SL-5和SL-110）、一个色素模式位点(r)和一个雄性决定因子(y)。从互交的F1雄性中没有获得重组后代。相比之下，从SL-5和SL-110之间的F1雌性中获得了许多重组后代（>25%）。这些结果表明，XY型雄性和XX型雌性在重组率上存在显著差异。XY雄性的这种重组限制可能导致了橙红色雄性和白色雌性菌株d-rR的建立。为了阐明重组限制的机制，对性别反转鱼类进行了分离分析。

Using a male-determining factor-congenic strain of the Japanese medaka, Oryzias latipes, we screened a genomic DNA library and isolated two sex-linked DNA clones, SL-5 and SL-110. The nucleotide sequences were completely determined. SL-5 was a single-copy sequnece 1.7 kb in size. SL-110 was a repetitive sequence 498 b in length.We designed PCR primer sets at both ends of these clones. Length of the PCR product using the SL-5 primer sets was different between two inbred strains, Hd-rR and HNI.The PCR product using SL-110 primer sets gave different cleavage patterns between these strains when degested by Hae III.Segregation of a total of four loci, which included two DNA loci (SL-5 and SL-110), a pigment-pattern locus (r) and a male-determining factor (y), were examined using backcrosses of Hd-rR and HNI.No recombinant progeny were obtained from F1 males of the reciprocal crosses. By contrast, many recombinant progeny (>25%) were obtained from F1 females between SL-5 and SL-110.These results indicates that marked difference in recombination rate exists between XY nales and XX females. Such recombination restriction in XY males may have allowed the establishment of the orange-red male and white female strain, d-rR.In order to elucidate the mechanism of recombination restriction, segregation analyzes of sex-reversed fish are in progress.