Abstract
Cytogenomics, the integration of cytogenetic and genomic data, has been used here to reconstruct the evolution of chromosomes 2 and 4 of Solea senegalensis. S. senegalensis is a flat fish with a karyotype comprising 2n = 42 chromosomes: 6 metacentric + 4 submetacentric + 8 subtelocentric + 24 telocentric. The Fluorescence in situ Hybridization with Bacterial Artificial Chromosomes (FISH-BAC) technique was applied to locate BACs in these chromosomes (11 and 10 BACs in chromosomes 2 and 4, respectively) and to generate integrated maps. Synteny analysis, taking eight reference fish species (Cynoglossus semilaevis, Scophthalmus maximus, Sparus aurata, Gasterosteus aculeatus, Xiphophorus maculatus, Oryzias latipes, Danio rerio, and Lepisosteus oculatus) for comparison, showed that the BACs of these two chromosomes of S. senegalensis were mainly distributed in two principal chromosomes in the reference species. Transposable Elements (TE) analysis showed significant differences between the two chromosomes, in terms of number of loci per Mb and coverage, and the class of TE (I or II) present. Analysis of TE divergence in chromosomes 2 and 4 compared to their syntenic regions in four reference fish species (C. semilaevis, S. maximus, O. latipes, and D. rerio) revealed differences in their age of activity compared with those species but less notable differences between the two chromosomes. Differences were also observed in peaks of divergence and coverage of TE families for all reference species even in those close to S. senegalensis, like S. maximus and C. semilaevis. Considered together, chromosomes 2 and 4 have evolved by Robertsonian fusions, pericentric inversions, and other chromosomal rearrangements mediated by TEs.
Highlights
Cytogenomics is a methodology in which the cytogenetic and genomic data obtained are integrated
The integrated maps were generated from analysis of cytogenetic, BAC sequencing and microsynteny data (Figure 2)
The colors represent the different BACs in the chromosome maculatus, Oryzias latipes, Danio rerio, and Lepisosteus oculatus
Summary
Cytogenomics is a methodology in which the cytogenetic and genomic data obtained are integrated. The evolutionary dynamics of TEs are important, for genome size but, because the regrouping of mobile elements can originate differences in the number and structure of the chromosomes in some species [5]. Several different lines of evidence, such as the number of chromosomal rearrangements, functionalization of duplicated genes, rate of protein evolution, and conservation of non-coding elements, show a higher rate of evolution in teleosts than in other vertebrates. This group presents small chromosomes and an ancestral karyotype of 48 acrocentric chromosomes [12,13]. S. senegalensis (classified as metacentric and submetacentric, respectively) by comparing them with other available species and analyzing their repetitive elements
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