Recent progress of molecular cytogenetic study on scleractinian (stony) corals

Chromosome study of scleractinian (stony) corals had been restricted to only counting chromosome numbers and measuring their lengths to delineate the chromosome types to establish their karyotypes for the past thirty years (before 2012), because chromosome preparations, which were made by the conventional squash-method, had not been suitable for molecular cytogenetic techniques. To advance the chromosome analysis of stony corals, it was necessary to utilize a molecular cytogenetic technique, such as fluorescence in situ hybridization (FISH) with DNA probes. We devised a newly improved method for suitable chromosome preparations made from coral embryos for FISH and made significant progress in molecular cytogenetic study of stony corals by FISH using our methods for making chromosome preparations. FISH made it feasible to carry out the establishment of their precise karyotypes, the gene mapping, FISH marker isolation and ascertainment of sex chromosome in stony corals. Molecular cytogenetics is useful for connecting and understanding the gap in classification between morphological and molecular (DNA sequences) analyses in the scleractinia. Therefore, better understanding of chromosome features may help to integrate the systematics of the data from both morphology and molecular sequences of stony corals. This review offers an overview of our research on molecular cytogenetics of stony corals; we are presenting our new findings on some stony corals using FISH, and overviewing former cytogenetic reports. The information provided here should be useful for the ongoing study of stony coral chromosome evolution, classification, genetics, and genome projects.