Dispersion of transposable elements and multigene families: Microstructural variation in Characidium (Characiformes: Crenuchidae) genomes

Eukaryotic genomes consist of several repetitive DNAs, including dispersed DNA sequences that move between chromosome sites, tandem repeats of DNA sequences, and multigene families. In this study, repeated sequences isolated from the genome of Characidium gomesi were analyzed and mapped to chromosomes in Characidium zebra and specimens from two populations of C. gomesi. The sequences were transposable elements (TEs) named retroelement of Xiphophorus (Rex); multigene families of U2 small nuclear RNA (U2 snRNA); and histones H1, H3, and H4. Sequence analyses revealed that U2 snRNA contains a major portion corresponding to the Tx1-type non-LTR retrotransposon Keno, the preferential insertion sites of which are U2 snRNA sequences. All histone sequences were found to be associated with TEs. In situ localization revealed that these DNA sequences are dispersed throughout the autosomes of the species, but they are not involved in differentiation of the specific region of the W sex chromosome in C. gomesi. We discuss mechanisms of TE invasion into multigene families that lead to microstructural variation in Characidium genomes.