Molecular cytogenetic characterization of telomere-specific repetitive DNA sequences in Rana rugosa

We performed a molecular cloning of the glutamic oxaloacetic transaminase (GOT1) gene from R. rugosa, and determined its chromosomal location. This gene was reportedly localized near the sex-determining region of the ZW sex chromosomes in the frog Buergeria buergeri; however, the GOT1 gene was mapped to the distal end of chromosome 9 in R. rugosa using a GOT1 cDNA FISH probe. This was also the case when a 46.3kb genomic clone containing exon 8 and 9 and the 3'-neighboring region of the GOT1 gene, designated clone B, was used as probe. However, weak signals were also detected at the telomeric ends of other autosomes and the Z sex chromosome, and near the centromeric region of the W sex chromosome. To intensify the signals, we used eight internal fragments in clone B and applied them to chromosome mapping. Consequently, only two fragments containing repeated sequence blocks produced hybridization signals; those signals were observed on autosomes and ZW sex chromosomes. The 3'-neighboring region contained two types of repeated sequence elements: a 41bp element, designated 41-REL, localized to telomeric ends of autosomes and a 31bp element, designated 31-REL, localized to telomeric ends of all autosomes and the ZW sex chromosomes, and also near the centromere on the W long arm. The results collectively suggest that the two repeated sequence elements were independently amplified around the chromosomal telomeres in R. rugosa, indicating that they will be useful cytogenetic markers for studying karyotypic evolution-especially the W chromosome differentiation-in this species.