Chromosomal organization of repetitive DNA sequences in Astyanax bockmanni (Teleostei, Characiformes): dispersive location, association and co-localization in the genome

Abstract

Repetitive DNA sequences constitute a great portion of the genome of eukaryotes and are considered key components to comprehend evolutionary mechanisms and karyotypic differentiation. Aiming to contribute to the knowledge of chromosome structure and organization of some repetitive DNA classes in the fish genome, chromosomes of two allopatric populations of Astyanax bockmanni were analyzed using classic cytogenetics techniques and fluorescent in situ hybridization, with probes for ribosomal DNA sequences, histone DNA and transposable elements. These Astyanax populations showed the same diploid number (2n = 50), however with differences in chromosome morphology, distribution of constitutive heterochromatin, and location of 18S rDNA and retroelement Rex3 sites. In contrast, sites for 5S rDNA and H1, H3 and H4 histones showed to be co-located and highly conserved. Our results indicate that dispersion and variability of 18S rDNA and heterochromatin sites are not associated with macro rearrangements in the chromosome structure of these populations. Similarly, distinct evolutionary mechanisms would act upon histone genes and 5S rDNA, contributing to chromosomal association and co-location of these sequences. Data obtained indicate that distinct mechanisms drive the spreading of repetitive DNAs in the genome of A. bockmanni. Also, mobile elements may account for the polymorphism of the major rDNA sites and heterochromatin in this genus.

Chromosomal Mapping of Repetitive DNA Sequences in Five Species of <b><i>Astyanax</i></b> (Characiformes, Characidae) Reveals Independent Location of U1 and U2 snRNA Sites and Association of U1 snRNA and 5S rDNA

“…The histone clusters were localized in accordance with previous studies performed by Hashimoto et al [2010] and Silva et al [2013Silva et al [ , 2014, showing conserved positions in 4 chromosome pairs in all the analyzed species. Notably, A. jordani was the only species that did not have synteny between histone genes and minor ribosomal sites ( fig.…”

“…Moreover, the occurrence of different types of B chromosomes in their cells, the existence of distinct karyotype formulas, and the differential distribution of repetitive DNAs in closely and distantly related species all reinforce the intense and continuous dynamics of the Astyanax genome, which includes macro-chromosomal rearrangements (e.g. fissions, fusions, and inversions) and changes at the sub-chromosomal level of resolution [Fernandes and Martins-Santos, 2005;Mantovani et al, 2005;Pazza et al, 2006;Carvalho et al, 2008;Hashimoto et al, 2008;Vicari et al, 2008;Daniel et al, 2012;Santos et al, 2013;Silva et al, 2013].…”

Chromosomal Mapping of Repetitive DNA and Cytochrome C Oxidase I Sequence Analysis Reveal Differentiation among Sympatric Samples of <b><i>Astyanax</i></b><b><i>fasciatus</i></b> (Characiformes, Characidae)

“…In the present study, the H1 and H3 histone clusters are colocalized and conserved in the same chromosome pair in both karyomorphs, corroborating previous data for the genus Astyanax [Hashimoto et al, 2011;Silva et al, 2013] and reinforcing the conserved distribution pattern of these sequences. Initial data reporting the location of the histone sequences in fish chromosomes suggested a tandem arrangement and location in a single chromosomal locus [Pendás et al, 1994b].…”

“…Notwithstanding, these few terminal heterochromatic blocks found in both karyomorphs contained the mobile element Rex3 ( figs. 1 , 4 ), an association also observed in other Astyanax species [Silva et al, 2013].…”

“…In 2 allopatric populations of A . bockmanni , NOR polymorphisms were associated with the colocalization of these sequences with the Rex3 retroelement [Silva et al, 2013]. The absence of associated Rex3 and 18S rDNA sites in the samples analyzed here indicates that different evolutionary forces are acting in the dispersion of the ribosomal sequences in Astyanax species.…”