Abstract
Molecular cytogenetic investigation based on fluorescence in situ hybridization (FISH) of the scleractinian coral, Echinophyllia aspera Ellis and Solander 1788, which is commonly found along temperate coasts in Japan (30-35°N) and in coastal waters in the Indian and Pacific oceans, was performed. FISH was applied in the study of this coral, using E. aspera embryo (about 9-12 hours after artificial fertilization; prawn chip stage). By genomic DNA hybridization (GDH) using DNA that was extracted from E. aspera embryos, we have succeeded in displaying the characteristic and distinct heterochromatin distribution, especially on telomeric regions of chromosomes, which may facilitate the classification of corals. FISH mapping of rRNA genes (rDNAs) was successfully carried out with the probe generated by PCR amplification using rRNA gene primers and revealed that extraordinary amplification of rDNA occurred in one of the homologous chromosomes similar to that in a homogeneous staining region (hsr) that is sometimes seen in human cancer cells. The presence of telomere sequences, (TTAGGG)n, in all chromosomes was visualized and demonstrated that this coral had the same sequences as humans. Based on these results obtained by FISH, we proposed the karyotype of this coral (2n = 28). Furthermore, we found that the telomeric heterochromatin in this coral contained the human satellite III DNA motif sequence (TTCCA)n, which is located on human chromosome 9 centromere. Taken together, these data suggest that karyotyping, rRNA gene mapping and heterochromatin motif sequences are useful tools for exploring the process of chromosome evolution, and phylogenetics of scleractinian coral.
