Organization of repeated DNA elements in the genome of the cichlid fish Cichla kelberi and its contributions to the knowledge of fish genomes.

Repeated DNA elements have been extensively applied as physical chromosome markers in comparative studies for the identification of chromosomal rearrangements, the identification of sex chromosomes, chromosome evolution analysis and applied genetics. Here, we report the characterization of the transposable elements (TE) Tc1, Rex1, Rex3 and Rex6 and a new element called RCk in the genome of the South American cichlid fish Cichla kelberi using nucleotide sequence analysis and hybridization to metaphase chromosomes. The analysis of the repeated elements demonstrated that they are, in most cases, compartmentalized in heterochromatic regions, as has been observed in several other vertebrates. On the other hand, the elements Rex1 and Rex3 were also observed spanning extensive euchromatic regions on 2 chromosome pairs. The RCk element exhibits a wide distribution among fishes and also in amphibians, and it was spread throughout the chromosomes of C. kelberi. Our results have demonstrated that the compartmentalization of repeated elements is not restricted to heterochromatic segments, which has provided new concepts with regard to the genomic organization of transposons. Copyright 2009 S. Karger AG, Basel.