New insights on the origin of B chromosomes in Astyanax scabripinnis obtained by chromosome painting and FISH

Abstract

Chromosome painting (CP) with a probe of B chromosome obtained by microdissection and fluorescence in situ hybridization (FISH) with probes of As51 satellite DNA, C( o )t-1 DNA, and 18S and 5S rDNA confirmed sharing of some repetitive DNA but not rDNA between A and B chromosomes in the fish Astyanax scabripinnis. Meiotic analysis revealed a pachytene B chromosome bivalent nearly half the size of its mitotic configuration, suggesting a self-pairing of B chromosome arms. Such an isochromosome nature of somatic B chromosome was further evidenced by CP and FISH. All the findings obtained suggest (i) intraspecific origin of B chromosome, and (ii) evolutionary enrichment of repetitive DNA classes, especially those contained in the C( o )t-1 and the As51 probes, in B chromosome. However, the precise origin of B chromosome in the present species remains to be elucidated by further molecular cytogenetic analysis because of painting of some A chromosome regions with the B chromosome-derived probe.

Cytogenetic characterization of distinct B chromosomes in a population of the fish Astyanax bockmanni (Teleostei, Characiformes)

“…In A. scabripinnis, structural and functional evidence suggest that B M corresponds to an isochromosome derived from an acrocentric chromosome of the standard karyotype (Mestriner et al 2000;Vicari et al 2011;Machado et al 2012). However, according to the isochromosomes origin, the centromere misdivision of an acrocentric chromosome ancestor and subsequent chromatid non-disjunction may simultaneously originate Conversely, our results showed the occurrence of B M and B microchromosome variants together in the same population, which supports the isochromosome origin of ).…”

“…a macrochromosome (B M ) similar in size to chromosome pair 1 and a microchromosome (B m ) similar in size to B a (Table 1 and Figure 2). Distinct B chromosomes have been described in several species of the genus Astyanax, and the most frequent variant is the metacentric macrochromosome (B M ) similar to chromosome pair 1, which might be considered the ancestral B chromosome with probably an early origin preceding the species differentiation (Moreira-Filho et al 2001;Vicari et al 2011;Machado et al 2012).…”

Evidence of incipient speciation in Astyanax scabripinnis species complex (Teleostei: Characidae)

“…However, the occurrence of more chromosome pairs carrying this rDNA has been registered (Ferro et al, 2001;Vicari et al, 2011). The presence of eight 5S rDNA sites in Astyanax, as verified in the present study in the Ribeirão Grande (662 m a.s.l.)…”

Karyotypic diversity among three species of the genus Astyanax (Characiformes: Characidae)

“…The first approach on the probable origin of this chromosome was performed by Salvador and Moreira-Filho (1992), who considered that a non-disjunction, followed by heterochromatinization, could be associated with its emergence. However strong evidence that this supernumerary is an isochromosome was given by some additional mitotic and meiotic studies, which also indicated that its heterochromatic nature is related with the amplification and dispersion of highly repetitive sequences (Mestriner et al, 2000;Moreira-Filho et al, 2004;Vicari et al, 2011).…”