Organization and Chromosomal Distribution of Histone Genes and Transposable<b><i> Rex</i></b> Elements in the Genome of <b><i>Astyanax bockmanni </i></b>(Teleostei, Characiformes)

Abstract

An important feature of eukaryotic organisms is the number of different repetitive DNA sequences in their genome, a feature not observed in prokaryotes. These sequences are considered to be important components for understanding evolutionary mechanisms and the karyotypic differentiation processes. Thus, we aimed to physically map the histone genes and transposable elements of the Rex family in 6 fish populations of Astyanax bockmanni. FISH results using a histone H1 gene probe showed fluorescent clusters in 2 chromosome pairs in all 6 samples analyzed. In contrast, FISH with a histone H3 probe showed conspicuous blocks in 4 chromosomes in 5 of the 6 populations analyzed. The sixth population revealed 7 chromosomes marked with this probe. Probes for the transposable elements Rex1 and Rex6 showed small sites dispersed on most chromosomes of the 6 populations, and the Rex3 element is located in a big block concentrated in only 1 acrocentric chromosome of 2 populations. As for the other populations, a Rex3 probe showed large blocks in more than 1 chromosome. Fish from Alambari and Campo Novo Stream have Rex3 elements dispersed along most of the chromosomes. Additionally, the conspicuous signals of Rex1, Rex3, and Rex6 were identified in the acrocentric B microchromosome of A. bockmanni found only in individuals of the Alambari River. Thus, we believe that different mechanisms drive the spread of repetitive sequences among the populations analyzed, which appear to be organized differently in the genome of A. bockmanni. The presence of transposable elements in the B chromosome also suggests that these sequences could play a role in the origin and maintenance of the supernumerary element in the genome of this species.

Paracentric Inversions Differentiate the Conservative Karyotypes in Two <b><i>Centropomus</i></b> Species (Teleostei: Centropomidae)

“…Molina Cytogenet Genome Res DOI: 10.1159/000499748 6 Similar to ribosomal genes, the histone multigene family plays a crucial role in the genomes of eukaryotes [Eirín-López et al, 2009]. The position of histone genes in the chromosomes of many fish species has been shown to be evolutionarily more dynamic than previously thought [Pansonato-Alves et al, 2013;Costa et al, 2014;Daniel et al, 2015;Utsunomia et al, 2016], and eventually they were co-located with ribosomal genes [Costa et al, 2016]. In Centropomus , mapping of the H2A-H2B sites revealed a single locus in both studied species in the long arms of the homeologous pair 14, suggesting evolutionary conservatism of this multigene family ( Fig.…”

Rex Retroelements and Teleost Genomes: An Overview

“…The physical mapping of Rex elements performed in six natural population of the neotropical fish A. bockmanni evidenced different patterns suggesting that different mechanisms drive the spread of repetitive sequences among the analyzed population [ 39 ]. Rex1 and Rex6 showed small clusters scattered on most chromosomes of the six populations.…”

“…This element was also mapped in the heterochromatic blocks of the congeneric species A. fasciatus sampled from the Tietê river [ 40 ]. Interestingly Rex1, Rex3, and Rex6 signals were detected in the acrocentric B chromosome of A. bockmanni specimens sampled from the Alambari river [ 39 ]. In addition, Fantinatti and colleagues [ 43 ] reported the detection of Rex1 and Rex3 signals in the B chromosomes of Astatotilapia latifasciata .…”

Chromosomal organization of retrotransposon Rex1 in Astyanax species (Characiformes, Characidae)

“…Other studies have already reported the distribution of retrotransposable elements in the chromosomes of species from Astyanax genus (Pansonato-Alves et al 2013;Silva et al 2013Silva et al , 2014Daniel et al 2015) (Table 1). Similar to our data, Rex1 presented a dispersed pattern of distribution in A. paranae (Silva et al 2014).…”

“…Given the important roles of retrotransposable elements on fish evolution, their mapping is very important for understanding the genome structure and evolution process in Astyanax (Characiformes, Characidae) genus (Silva et al 2013(Silva et al , 2014Daniel et al 2015;. Astyanax is an interesting group because present high karyotype diversity, including species with 2n = 52, 50, 48, 46 and 36 chromosomes (Tenório et al 2013;Piscor et al 2015;Nishiyama et al 2016;Piscor et al 2016;Parise-Maltempi 2016a, 2016b).…”