Molecular Cytogenetic Analysis and Isolation of a 5S rRNA-Related Marker in the Scleractinian Coral Platygyra contorta Veron 1990 (Hexacorallia, Anthozoa, Cnidaria)

A molecular cytogenetic analysis was conducted on the scleractinian coral Platygyra contorta, which is commonly found along temperate coasts in Japan. P. contorta was karyotyped (2n=28) by conventional G- and C-bandings, and the karyogram revealed that about 50% of the metaphase spreads had a homogenously staining region (hsr) in the terminal portion of the long arm of chromosome 12. Fluorescence in situ hybridization (FISH) showed that this hsr consisted of rRNA genes (rDNA) stained by C-banding. The presence of an hsr, which is a highly amplified rDNA, may explain the molecular diversity of coral rDNA. FISH visualized and demonstrated the presence of a telomere motif (TTA GGG)n in this coral using a human telomere probe. Furthermore, we isolated a specific FISH marker (312 bp) designated PC-T1, which was located near the centromere of chromosome 11. A sequence analysis revealed that the terminal part of PC-T1 (51 bp from the 3′ end) was 90% homologous with a Montipora capitate microsatellite and the Actinia equine 5S rRNA gene. Isolating FISH markers will assist the classification of scleractinian corals with the progression on describing their genome. The data obtained in this study will be valuable for discriminating species among scleractinian corals and understanding their genetics, including chromosomal evolution.