Karyotype and cytogenetic mapping of 9 classes of repetitive DNAs in the genome of the naked catfish Mystus bocourti (Siluriformes, Bagridae)

Abstract

BackgroundIn the present study, conventional and molecular cytogenetic studies were performed in the naked catfish Mystus bocourti (Siluriformes, Bagridae). Besides the conventional Giemsa staining, fluorescence in situ hybridization (FISH) using nine classes of repetitive DNAs namely 5S and 18S rDNAs, U2 snRNA, the microsatellites (CA)15 and (GA)15, telomeric repeats, and the retrotransposable elements Rex1, 3 and 6. was also performed.ResultsM. bocourti had 2n = 56 chromosomes with a karyotype composed by 11 m + 11 sm + 6 st/a and a fundamental number (NF) equal to 100 in both sexes. Heteromorphic sex chromosome cannot be identified. The U2 snRNA, 5S and 18S rDNA were present in only one pair of chromosomes but none of them in a syntenic position. Microsatellites (CA)15 and (GA)15 showed hybridization signals at subtelomeric regions of all chromosomes with a stronger accumulation into one specific chromosomal pair. FISH with the telomeric probe revealed hybridization signals on each telomere of all chromosomes and interstitial telomeric sites (ITS) were not detected. The retrotransposable elements Rex1, 3 and 6 were generally spread throughout the genome.ConclusionsIn general, the repetitive sequences were not randomly distributed in the genome, suggesting a pattern of compartmentalization on the heterochromatic region of the chromosomes. Little is known about the structure and organization of bagrid genomes and the knowledge of the chromosomal distribution of repetitive DNA sequences in M. bocourti represents the first step for achieving an integrated view of their genomes.

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

“…U1 and U2 snRNA genes showed a strong conservation in the number of sites per genome. Such a conserved feature seems to be common in different groups of fishes, with only 1 or few chromosomes per genome bearing these genes Cabral-de-Mello et al, 2012;Merlo et al, 2012 a, b;Supiwong et al, 2013;. In several cichlid species, the U1 snRNA is clustered in a single pair, in the same manner as can be found in Gymnotus species for the U2 snRNA.…”

Highly Similar Morphologies Between Chromosomes Bearing U2 snRNA Gene Clusters in the Group Astyanax Baird and Girard, 1854 (Characiformes, Characidae): An Evolutionary Approach in Species with 2n = 36, 46, 48, and 50

“…The chromosomal locations of the 5S rDNA and U2 snDNA clusters were not consistently linked in the Astyanax species examined here because that these represent two distinct classes of repetitive DNA with completely different functions. Supiwong et al 28 found that U2 snDNA and 5S rDNA sequences were also carried on different chromosome pairs in the naked catfish Mystus bocourti Bleeker, 1864 (Siluriformes). This spatial separation of 5S rDNA and U2 snDNA appears to be a common feature in fish (see, e.g., 29,30 ).…”

Comparative Chromosome Mapping of U2 snRNA and 5S rRNA Genes in <b><i>Gymnotus</i></b> Species (Gymnotiformes, Gymnotidae): Evolutionary Dynamics and Sex Chromosome Linkage in <b><i>G</i></b>. <b><i>pantanal</i></b>

“…For example, from the 5 existing subtypes of U snRNA genes, U1 snDNA was mapped only in cichlid species, and its position was highly conserved, with a single pair of U1 snDNA-bearing chromosomes for all analyzed species [Cabral-de-Mello et al, 2012]. Conversely, U2 snDNA cluster location was reported in 5 Batrachoididae, 2 Moronidae, 1 Bagridae, and 1 Haemulidae species [Merlo et al, , 2012aÚbeda-Manzanaro et al, 2010;Supiwong et al, 2013] and evidenced a more diversified scenario, particularly in the Batrachoididae family with species presenting (i) compartmentalization of this sequence in a single pair, (ii) a very widely scattered distribution throughout all chromosomes, or (iii) simultaneous scattered and compartmentalized organization [Úbeda-Manzanaro et al, 2010]. Here, we show that the U2 snDNA is compartmentalized and the number of U2 snDNAbearing chromosomes is conserved in Gymnotus .…”

“…The U snDNA is a multigene family of non-coding RNAs that compounds the spliceosome machinery and may be subdivided into 5 types, including U1, U2, U4, U5, and U6 [Valadkhan, 2005]. Although highly suitable for use as FISH probes, these sequences have been mapped in only few fish until now, U1 in 19 cichlid species [Cabral-de-Mello et al, 2012] and U2 in 8 species [Merlo et al, , 2012aÚbeda-Manzanaro et al, 2010;Supiwong et al, 2013]. Although scarce, data on physical mapping of U snRNA genes in different organisms evidence that these sequences may be linked with other multigene families [Pelliccia et al, 2001;Manchado et al, 2006], may present distinct patterns of chromosomal organization [Úbedo-Manzanaro et al, 2010] and may be allocated in sex or supernumerary chromosomes [Bueno et al, 2013;Palacios-Gimenez et al, 2013].…”