Delimiting the Origin of a B Chromosome by FISH Mapping, Chromosome Painting and DNA Sequence Analysis in Astyanax paranae (Teleostei, Characiformes)

Abstract

Supernumerary (B) chromosomes have been shown to contain a wide variety of repetitive sequences. For this reason, fluorescent in situ hybridisation (FISH) is a useful tool for ascertaining the origin of these genomic elements, especially when combined with painting from microdissected B chromosomes. In order to investigate the origin of B chromosomes in the fish species Astyanax paranae, these two approaches were used along with PCR amplification of specific DNA sequences obtained from the B chromosomes and its comparison with those residing in the A chromosomes. Remarkably, chromosome painting with the one-arm metacentric B chromosome probe showed hybridization signals on entire B chromosome, while FISH mapping revealed the presence of H1 histone and 18S rDNA genes symmetrically placed in both arms of the B chromosome. These results support the hypothesis that the B chromosome of A. paranae is an isochromosome. Additionally, the chromosome pairs Nos. 2 or 23 are considered the possible B chromosome ancestors since both contain syntenic H1 and 18S rRNA sequences. The analysis of DNA sequence fragments of the histone and rRNA genes obtained from the microdissected B chromosomes showed high similarity with those obtained from 0B individuals, which supports the intraspecific origin of B chromosomes in A. paranae. Finally, the population hereby analysed showed a female-biased B chromosome presence suggesting that B chromosomes in this species could influence sex determinism.

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

“…4 ). Among the repetitive DNA probes for U1 and U2 snRNA, 5S rDNA and histone genes were mapped, and only H1 histone sequences were located on the B chromosome of A. paranae , confirming previous results [Silva et al, 2014].…”

“…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.…”

“…The proximity of histone and 5S rDNA cluster sequences in one chromosome pair of several Characidae species led some authors to suggest a possible selective advantage provided by [Hashimoto et al, 2011;Silva et al, 2013Silva et al, , 2014. Remarkably, other co-localization occurrences involving different repetitive sequences have been reported in Astyanax , which can be useful for understanding the organization of the genome in these species, e.g.…”

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)

“…Similar patterns were also observed in other species of the genus [Pansonato-Alves et al, 2013a;Silva et al, 2014]. Additionally, individuals of the Alambari population present- ed 0-2 partially or fully heterochromatic metacentric and/or acrocentric supernumerary microchromosomes in their genome, with a morphologic behavior that was previously observed by Hashimoto et al [2011] and Daniel et al [2012.…”

“…fasciatus [Silva et al, 2013;Pansonato-Alves et al, 2013a], and according to Pansonato-Alves et al [2013a], these features converge to a common ancestry and a conservative behavior. This hypothesis was already proposed by Hashimoto et al [2011] and was subsequently corroborated and strengthened by Silva et al [2013Silva et al [ , 2014 and Pansonato-Alves et al [2013a]. The idea that these genes could evolve in concert was also reported and discussed for species in other fish groups Pansonato-Alves et al, 2013b;Utsunomia et al, 2014].…”