An Unusual Accumulation of Ribosomal Multigene Families and Microsatellite DNAs in the XX/XY Sex Chromosome System in the Trans-Andean Catfish Pimelodella cf. chagresi (Siluriformes:Heptapteridae)

Abstract

This work constitutes the first cytogenetic characterization of a trans-Andean species of Heptapteridae. The catfish Pimelodella cf. chagresi from the Upper Rio Magdalena was studied, applying standard cytogenetic techniques (Giemsa, C-banding, and argyrophilic nucleolar organizer region [Ag-NOR]) and fluorescence in situ hybridization techniques using repetitive DNA probes: microsatellites (CA and GA) and ribosomal RNA (rRNA) multigene families (18S and 5S recombinant DNA [rDNA] probes). The species showed a unique diploid chromosome number 2n = 50 (32m [metacentrics] +14sm [submetacentrics] +4st [subtelocentrics]) and a XX/XY sex chromosomal system, where the heteromorphic Y-chromosome revealed a conspicuous accumulation of all the assayed domains of repetitive DNA. P. cf. chagresi karyotype shares common features with other Heptapteridae, such as the predominance of metacentric and submetacentric chromosomes, and one pair of subtelomeric nucleolar organizer regions (NORs). These results reflect an independent karyological identity of a trans-Andean species and the relevance of repetitive DNA sequences in the process of sex chromosome differentiation in fish; it is the first case of syntenic accumulation of rRNA multigene families (18S and 5S rDNA) and microsatellite sequences (CA and GA) in a differentiated sex chromosome in Neotropical fish.

Karyotypic variation of two populations of the small freshwater stingray Potamotrygon wallacei Carvalho, Rosa & Araújo 2016: A classical and molecular approach

“…Although the association between sex chromosomes and (AG) 15 and (AC) 15 motifs have been reported in some bone fish [61,62], our data follow the general pattern found in other groups, showing pericentromeric and terminal clusters in autosomal chromosomes [50,62,66]. In this case, these microsatellite clusters might play a structural role and the pattern found here must be a result of different pressures that shaped the distribution of these SSRs in the karyotype in the P. wallacei.…”

“…Although the association of SSRs motifs with sex chromosomes has been documented in many vertebrate groups [24,25,27,51,61,62], unfortunately, data about the distribution of SSRs in Potamotrygoninae species are limited to the present study. While most of SSRs used here showed amplification in several chromosomes, (GATA) 4 motif was associated with the X chromosome in P. wallacei (two sites in the female and one in males).…”

Evolutionary rearrangements of X chromosomes in voles (Arvicolinae, Rodentia)

“…The use of AT-/GC-specific fluorochromes discovered great variability in the heterochromatin composition 56 . Simple repetitive sequences (e.g., microsatellites) are often accumulated in high copy numbers on the sex chromosomes in many taxa 57 - 59 , although the same repeats can be distributed throughout the genome in low copy numbers 55 . But in some species moderately repetitive sequences rather than highly repetitive DNA represent blocks of heterochromatin.…”

Cytogenetic Trends in Two Families of the Neotropical Catfishes: Heptapteridae and Pseudopimelodidae (Siluriformes)

“…The location and number of the rDNA 5S are relatively variable occupying preferentially interstitial regions on one chromosome pair or two chromosome pairs (Table 1), in some cases syntenic with regions rDNA 18S, as already described by other authors. 11,16,25,[32][33][34] Gouveia et al 25,33 isolated 5S rDNA sequences and transposon (Tc1-mariner) from I. schubarti genome and found that transposable elements may be acting along these sequences, showing hybridization in some species of Heptapteridae and Pseudopimelodidae, and seem to be related to the movement of 5S rDNA genes in these fish genomes. Recently, Souza-Shibatta et al 35 reevaluated M. cottoides systematics, using morphological and molecular data, with sequence analysis of the COI (cytochrome oxidase I) gene.…”