Whole chromosome painting of B chromosomes of the red-eye tetra Moenkhausia sanctaefilomenae (Teleostei, Characidae)

Abstract

B chromosomes are dispensable genomic elements found in different groups of animals and plants. In the present study, a whole chromosome probe was generated from a specific heterochromatic B chromosome occurring in cells of the characidae fish Moenkhausia sanctaefilomenae (Steindachner, 1907). The chromosome painting probes were used in fluorescence in situ hybridization (FISH) experiments for the assessment of metaphase chromosomes obtained from individuals from three populations of Moenkhausia sanctaefilomenae. The results revealed that DNA sequences were shared between a specific B chromosome and many chromosomes of the A complement in all populations analyzed, suggesting a possible intra-specific origin of these B chromosomes. However, no hybridization signals were observed in other B chromosomes found in the same individuals, implying a possible independent origin of B chromosome variants in this species. FISH experiments using 18S rDNA probes revealed the presence of non-active ribosomal genes in some B chromosomes and in some chromosomes of the A complement, suggesting that at least two types of B chromosomes had an independent origin. The role of heterochromatic segments and ribosomal sequences in the origin of B chromosomes were discussed.

Uncovering the Ancestry of B Chromosomes in Moenkhausia sanctaefilomenae (Teleostei, Characidae)

“…To date, all studied populations of M . sanctaefilomenae harbour B chromosomes [ 21 – 25 ]. Since their first description, several authors have proposed the occurrence of three B types in this species, distinguishable by their C-banding patterns [ 21 , 24 ].…”

“…Since their first description, several authors have proposed the occurrence of three B types in this species, distinguishable by their C-banding patterns [ 21 , 24 ]. Recently, it was reported that some B chromosomes in this species carry 18S rDNA clusters, while others do not [ 25 ]. In the present study, C-banding and FISH analyses allowed us to clearly identify only two different B types, which showed differences in terms of C-banding patterns, the abundance of 18S rDNA and population frequency.…”

“…sanctaefilomenae are composed of the same repetitive DNA sequences, suggesting a common intraspecific origin of these chromosomes. Recently, Scudeler et al [ 25 ] suggested an intraspecific origin of B chromosomes in this species, based on WCP results indicating the presence of DNA sequences shared between A and B chromosomes. Our present results are consistent with this conclusion.…”

“…M . sanctaefilomenae shows a conserved karyotype with respect to the standard genome (2n = 50 biarmed chromosomes) but also carries micro-B chromosomes in all populations hitherto analyzed [ 21 – 25 ]. Specifically, several populations collected in the Tietê River basin show euchromatic, or partially or totally heterochromatic B chromosomes [ 21 , 23 – 25 ], whereas one population collected in the Paraná River shows only the euchromatic variant, which is restricted to males [ 22 ].…”

“…Recently, after karyotyping three populations from the Tietê River basin and performing chromosome painting using a B-specific probe, Scudeler et al [ 25 ] concluded that the heterochromatic B type had an intraspecific origin, due to sharing DNA sequences with several A chromosomes, and that it arose independently from the euchromatic B chromosome, as a painting probe produced from the former B type did not paint the latter variant. In an attempt to extend these conclusions further, in the present study, we analyzed a natural population carrying the euchromatic and heterochromatic variants by means of a combination of cytogenetic (C-banding, microdissection, chromosome painting, FISH mapping, silver staining), molecular (PCR amplification, cloning, Sanger DNA sequencing and Illumina sequencing), phylogenetic, and bioinformatics techniques, additionally providing the first report for a B-lacking population in this species.…”