Unusual Dispersion of Histone Repeats on the Whole Chromosomal Complement and Their Colocalization with Ribosomal Genes in <b><i>Rachycentron canadum</i></b> (Rachycentridae, Perciformes)

Abstract

Rachycentron canadum, the only representative of the family Rachycentridae, has been the focus of biotechnological interest due to its significant potential in marine fish farming. The chromosome set of this species has been widely investigated with respect to the location of genes and multigene families. A FISH analysis was performed using 4 multigene families as probes, represented by 5S and 18S ribosomal genes and histones H2B-H2A and H3. Earlier data suggested that differential replication of heterochromatin could be partially associated with functional genes. Indeed, our results showed that the DNA contained in heterochromatic regions of R. canadum contains 5S and 18S ribosomal genes as well as the gene sequences of histones H2B-H2A and H3, which were colocalized. The distribution of H3 sequences in all heterochromatic regions, except in 13q, could indicate an important evolutionary role for this class of repetitive sequences. Besides, the presence of chromosome regions bearing multifunctional repetitive sequences formed by H2B-H2A/H3/18S rDNA and H2B-H2A/H3/5S rDNA clusters was demonstrated for the first time in fishes. The implications of differential histone gene extension and its functionality in the karyotype of R. canadum remain unknown.

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

“…Nonetheless, an unusual pattern with signals dispersed on 22 chromosome pairs in Ocyurus chrysurus has also been recorded [Costa et al, 2016]. In R. canadum (Rachycentridae), H3 sites were also scattered and located on all 24 chromosome pairs of the karyotype, forming complex arrangements of H2A-H2B/H3/18S rDNA and H2A-H2B/H3/5S rDNA chromosomal regions [Costa et al, 2014]. Like the 18S rDNA, the multiple H3 sites displayed distinct positions in the 3 homeologous pairs in the 2 snook species.…”

“…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.…”

Structurally Complex Organization of Repetitive DNAs in the Genome of Cobia (Rachycentron canadum)

“…This distribution pattern also suggests that not all H3 (48 in total) and H2B-H2A sites (24 in total) could be genetically active, in spite of their generally conserved condition. [46][47][48] On the other hand, extensive chromosome mapping of different repetitive sequences in the chromosomes of this species [20][21][22] has shown the functional coexistence between active genetic regions and different repetitive DNA classes.…”

“…The (GA) 15 sequences were exclusively located in the heterochromatic regions coinciding with the C-banding pattern in the chromosomes. 22 Clusters of these microsatellites were grouped in telomeric, centromeric, and pericentromeric regions of most chromosome arms, some of them more extensive than others (Fig. 1).…”

Chromosomal mapping of H3 histone and 5S rRNA genes in eight species of Astyanax (Pisces, Characiformes) with different diploid numbers: syntenic conservation of repetitive genes

“…Unlike the rDNA sequences, histone genes are generally found on one or two chromosome pairs in vertebrates, including mammals (Graves et al 1985;Tripputi et al 1986), amphibian (Turner et al 1988), and fish (Pendás et al 1994a;Hashimoto et al 2011Hashimoto et al , 2013Silva et al 2014;Costa et al 2014). Few investigations of histone gene locations in fish have been described in the literature.…”