Evolutionary Dynamics of Multigene Families in Triportheus (Characiformes, Triportheidae): A Transposon Mediated Mechanism?

Abstract

Triportheus (Characiformes, Triportheidae) is a freshwater fish genus with 18 valid species. These fishes are widely distributed in the major river drainages of South America, having commercial importance in the fishing market, mainly in the Amazon basin. This genus has diverged recently in a complex process of speciation carried out in different river basins. The use of repetitive sequences is suitable to trace the genomic reorganizations occured along the speciation process. In this work, the 5S rDNA multigene family has been characterized at molecular and phylogenetic level. The results showed that other multigene family has been found within the non-transcribed spacer (NTS): the U1 snRNA gene. Double-FISH with 5S and U1 probes were also performed, confirming the close linkage between these two multigene families. Moreover, evidences of different transposable elements (TE) were detected within the spacer, thus suggesting a transposon-mediated mechanism of 5S-U1 evolutionary pathway in this genus. Phylogenetic analysis demonstrated a species-specific grouping, except for Triportheus pantanensis, Triportheus aff. rotundatus and Triportheus trifurcatus. The evolutionary model of the 5S rDNA in Triportheus species has been discussed. In addition, the results suggest new clues for the speciation and evolutionary trend in these species, which could be suitable to use in other Characiformes species.

Cytogenetic Analysis of <b><i>Panaqolus tankei</i></b> Cramer &amp; Sousa, 2016 (Siluriformes, Loricariidae), an Ornamental Fish Endemic to Xingu River, Brazil

“…debilittera. In Triportheus Cope (1872) species on the other hand, the spreading of 5S rDNA is ruled by the association of this sequence with the U1 multigenic family in addition to transposable elements found in the non-transcribed spacer, which suggests that this gene has been frequently subjected to transposition events [Yano et al, 2020]. Barros et al [2017] raised the hypothesis that 5S rDNA pseudogenes strongly act as hotspots for chromosomal breaks, and consequently are directly involved in the variation of these ribosomal sequences in Loricariidae species.…”

Taxonomic Diversity Not Associated with Gross Karyotype Differentiation: The Case of Bighead Carps, Genus Hypophthalmichthys (Teleostei, Cypriniformes, Xenocyprididae)

“…What is less conserved, is the so far known association of U2 snDNA with other multigene families. Several combinations of syntenic/adjacent or intermingled arrangements can be found among fishes such as between 5S rDNA and U1 snDNA [47,85], 5S rDNA and U2 snDNA [84,98,100,105], 18S rDNA with U2 snDNA [99,106,108], 5S and 18S rDNA together with U2 snDNA [99] and even with several histone genes [109]; further U1 and U2 snDNA [97,104] or U1 and U2 snDNA together with 5S rDNA [110]. Therefore, these arrangements may potentially serve as useful cytotaxonomic markers.…”

“…A difference in number of 5S rDNA clusters between emerald and darter goby (two vs. 42) [81] may serve as an illustrative example. Besides the difference in number and position of positive signals, also the linkage between 45S and 5S or them with other multigene families may represent a valuable cytotaxonomic determiner (see, e.g., in [82][83][84][85]).…”

“…Genes for small nuclear RNA (snRNA) are yet readily used for chromosome mapping in fishes, though studies employing U2 snDNA as a cytogenetic marker are steadily growing in the last years ([84,97-101], to name a few). On the other hand, U1 snDNA has been so far chromosomally mapped only in a cichlid Oreochromis niloticus [102], several South American characiforms of the genera Astyanax [47] and Triportheus [85], and further in African characiform representative Hepsetus odoe [103], one species from Gadiformes [104] and one taxon (suspected species complex) belonging to Mugiliformes [73]. Among cypriniforms, only a single recent work mapped U2 snDNA sites, namely in diploid and tetraploid loaches of the family Botiidae [49], therefore our present study is the first one showing the position of U1 snDNA on cypriniform chromosomes.…”

The role of repetitive DNA in re-patterning of major rDNA clusters in Lepidoptera

“…IGSs are known to contain repetitive motives, which usually do not correspond to MEs (Grozdanov et al, 2003; Havlová et al, 2016). However, association between rDNA and MEs has been reported with 5S being involved more often than 45S rDNA (da Silva et al, 2016; Yano et al, 2020). Insertions of MEs into IGS observed in H. humuli thus represents interesting case of complex repeat organization (cf.…”