Chromosome Mapping of Retrotransposable Elements <i>Rex1</i> and <i>Rex3</i> in Three Fish Species in the Subfamily Hypoptopomatinae (Teleostei, Siluriformes, Loricariidae)

Abstract

Transposons and retrotransposons represent a great portion of the eukaryotic genome. These repeated elements can be defined as genetic entities capable of self-inserting into different positions within the genome modifying the functions of the genes with which they are associated. The purpose of the present work was to isolate, identify, and map the sequences of Rex1 and Rex3 transposable elements present in the genomes of fishes of the family Loricariidae. The retrotransposable elements were identified through amplification with Rex1 and Rex3 primers, and the nucleotide composition of the retrotransposons was determined by automatic sequencing. In all the species analyzed it was possible to isolate Rex1 partial sequences from 520 to 563 bp in size and Rex3 partial sequences from 407 to 454 bp in size. Comparisons with the available literature showed that Loricariidae retrotransposons Rex1 and Rex3 have a high sequence similarity to putative homologous genes in different fish orders. Fluorescence in situ hybridization experiments conducted in 3 species, Hisonotus leucofrenatus, Pseudotocinclus tietensis, and Parotocinclus maculicauda, using the retrotransposable elements isolated for each species as probes, revealed that Rex1 and Rex3 share a similar dispersion pattern and are both found on all chromosomes of the 3 species organized in small clusters and dispersed on all the chromosomes, including euchromatic and heterochromatic regions, although a larger concentration was observed in the heterochromatic regions of H. leucofrenatus. The data found in the present study contradict much of the literature that substantiates that the retrotranspon elements are preferentially accumulated in the heterochromatin regions in fishes.

The role of chromosomal fusion in the karyotypic evolution of the genus Ageneiosus (Siluriformes: Auchenipteridae)

“…The hybridization with the [GATA] n sequence showed correspondence with the heterochromatin in the terminal region of almost all chromosomes, also being present in lower amount in interstitial regions, and coincident with the unique C-band in the pericentromeric region (pair 1). This situation in which repetitive elements have been found widely dispersed in the genomes is relatively common and has been observed in other fish species recently (e.g., Teixeira et al, 2009;Ferreira et al, 2011).…”

Transposable elements as a potential source for understanding the fish genome

“…Studies carried with the retrotransposons Rex1 and Rex3 in three species of the subfamily Hypoptopomatinae by Ferreira et al 46 disclosed a genomic organization sufficiently differentiated from that found among the representatives of other orders of fish already studied. Such elements are spread throughout the genome of the species and are more intensely present in the euchromatic regions of the chromosomes.…”

“…However, some blocks of TEs are coincident with the heterochromatic regions, suggesting that the standard of distribution of these retroelements can be distinct in the different orders of fish. 46 However, the authors also admit there are factors, such as the stringency in the application of the FISH technique, which may justify the differences found, since the perfect visualization of the markings provided by this technique depends on the number of TEs copies in the genome and on the degree of stringency applied in the technical experiments.…”

A new dispersed element in the genome of the catfish Hisonotus leucofrenatus (Teleostei

“…13 In this study, the retroelements Rex1 and Rex3 were analyzed and presented dispersed patterns of distribution in the genome, in a similar way to that found for the HLBam transposable element. This feature reinforces the hypothesis proposed by Ferreira et al 4 that all transposable elements behave similarly within a family or subfamily.…”

“…There are only a few studies on the identification and chromosome location of these elements in fish, and the data on physical genome mapping are still restricted to 15 transposable elements mapped onto the genome of 32 species. 4 The dispersed pattern of marks evidenced by FISH technique with the single HLBam element in H. leucofrenatus has been described before in the Antarctic Perciformes 12 and in individuals of the subfamily Hypoptopomatinae by Ferreira et al 13 when studying the retrotransposons Rex1 and Rex3. The finding on the genomic organization of this element supports the hypothesis that the isolated HLBam sequence is a dispersed transposon type element.…”