RESUMEN
Despite conservation of the diploid number, a huge diversity in karyotype formulae is found in the Ancistrini tribe (Loricariidae, Hypostominae). However, the lack of cytogenetic data for many groups impairs a comprehensive understanding of the chromosomal relationships and the impact of chromosomal changes on their evolutionary history. Here, we present for the first time the karyotype of Panaqolus tankei Cramer & Sousa, 2016. We focused on the chromosomal characterization, using conventional and molecular cytogenetic techniques to unravel the evolutionary trends of this tribe. P. tankei, as most species of its sister group Pterygoplichthini, also possessess a conserved diploid number of 52 chromosomes. We observed heterochromatin regions in the centromeres of many chromosomes; pairs 5 and 6 presented interstitial heterochromatin regions, whereas pairs 23 and 24 showed extensive heterochromatin regions in their q arms. In situ localization of 18S rDNA showed hybridization signals correlating with the nucleolus organizer regions, which are located in the q arms of pair 5. However, the 5S rDNA was detected in the centromeric and terminal regions of the q arms of pair 8. (TTAGGG)n hybridized only in the terminal regions of all chromosomes. Microsatellite in situ localization showed divergent patterns, (GA)15 repeated sequences were restricted to the terminal regions of some chromosomes, whereas (AC)15 and (GT)15 showed a scattered hybridization pattern throughout the genome. Intraspecific comparative genomic hybridization was performed on the chromosomes of P. tankei to verify the existence of sex-specific regions. The results revealed only a limited number of overlapping hybridization signals, coinciding with the heterochromatin in centromeric regions without any sex-specific signals in both males and females. Our study provides a karyotype description of P. tankei, highlighting extensive differences in the karyotype formula, the heterochromatin regions, and sites of 5S and 18S rDNA, as compared with data available for the genus.
Asunto(s)
Bagres/genética , Cromosomas/genética , Análisis Citogenético/métodos , Cariotipificación/métodos , Animales , Brasil , Centrómero/genética , Hibridación Genómica Comparativa/métodos , Diploidia , Femenino , Heterocromatina , Hibridación Fluorescente in Situ/métodos , Cariotipo , Masculino , Región Organizadora del Nucléolo/genética , ARN Ribosómico 18S/genética , ARN Ribosómico 5S/genética , RíosRESUMEN
Pimelodidae has a high number of species, but cytogenetic studies are generally restricted to classical chromosomal characterization and in situ localization of ribosomal DNA (rDNA) genes. This study was developed to compare Pimelodus microstoma and Pimelodus pohli focusing on chromosomal diversification provided by the transposition of DNA sequences containing multigene families. Both species share 56 chromosomes, with centromeric and terminal heterochromatic blocks. The silver nucleolus organizer regions (Ag-NORs)/45S rDNA was located in the chromosome pair 24 for both species. The 5S rDNA sites were evidenced in the pair 8 of P. microstoma, and in the pairs 1, 17, and 18 in P. pohli. The U1 small nuclear RNA (snRNA) was located at terminal site in the first subtelocentric pair in both species. The U2 snRNA site was syntenic to 5S rDNA in non-homeologue chromosomes between analyzed species. The histones H3 and H4 were clustered in chromosome pairs 19 and 23 in P. microstoma, and 21 and 22 in P. pohli. Our study proposes that the movement of DNA sequences carrying multigene families has been driven on the chromosomal diversification of Pimelodidae. These multigene location in the genomes can explain most of the visualized chromosomal rearrangements in Pimelodidae and it is useful to understand the chromosomal changes and their distinctive karyotype formulae.