Chromosomal mapping of the major and minor ribosomal genes, (GATA)n and U2 snRNA gene by double-colour FISH in species of the Batrachoididae family

Abstract

In the present study dual-colour fluorescence in situ hybridization (FISH) was performed to study the chromosomal distribution of 18S and 5S rDNAs, (GATA)n and 5S rDNA, and U2 snRNA and 18S rDNA in four species of Batrachoididae family: Amphichthys cryptocentrus, Batrachoides manglae, Porichthys plectrodon and Thalassophryne maculosa. The 18S rDNA signals were present in only one pair of chromosomes in all the four Batrachoididae species. The 5S rDNA was mapped on one pair of chromosomes, except in B. manglae, which showed a hybridization signal in two pairs. The two ribosomal genes are located on different chromosome pairs, except in A. cryptocentrus, in which they appear co-located. In all the cases, the (GATA)n probe produced disperse hybridization signals in all four species. The U2 snRNA signals appear very widely scattered in A. cryptocentrus, P. plectrodon, but show a degree of clustering in a specific chromosome pair in B. manglae. In T. maculosa, they are thinly dispersed and strong hybridization signals are observed co-located to the 18S rDNA-bearing chromosomes. Finally, a double-colour FISH with U2 snRNA and 5S rDNA probes was performed in B. manglae, and this showed that these genes were not co-located. These results have been compared with those from another Batrachoididae species, and evolutive processes of these species are discussed.