Genome Compositional Organization in Gars Shows More Similarities to Mammals than to Other Ray‐Finned Fish. Issue 7 (30th December 2016)

• Record Type: Journal Article
• Authors: Symonová, Radka; Majtánová, Zuzana; Arias‐Rodriguez, Lenin; Mořkovský, Libor; Kořínková, Tereza; Cavin, Lionel; Pokorná, Martina Johnson; Doležálková, Marie; Flajšhans, Martin; Normandeau, Eric; Ráb, Petr; Meyer, Axel; Bernatchez, Louis
• Other Names: Braasch Ingo guestEditor.; Postlethwait John H. guestEditor.
• Is Part Of: Journal of experimental zoology. Volume 328:Issue 7(2017)
• Page Start: 607
• Page End: 619
• Publication Date: 2016-12-30
• Subjects: Developmental biology -- Periodicals; Evolution (Biology) -- Periodicals; Molecular evolution -- Periodicals; Zoology -- Periodicals; Evolution, Molecular -- Periodicals; Developmental Biology -- Periodicals; Zoology -- Periodicals; 591
• DOI: 10.1002/jez.b.22719
• Languages: English
• ISSNs: 1552-5007

Abstract

ABSTRACT: Genomic GC content can vary locally, and GC‐rich regions are usually associated with increased DNA thermostability in thermophilic prokaryotes and warm‐blooded eukaryotes. Among vertebrates, fish and amphibians appeared to possess a distinctly less heterogeneous AT/GC organization in their genomes, whereas cytogenetically detectable GC heterogeneity has so far only been documented in mammals and birds. The subject of our study is the gar, an ancient "living fossil" of a basal ray‐finned fish lineage, known from the Cretaceous period. We carried out cytogenomic analysis in two gar genera ( Atractosteus and Lepisosteus ) uncovering a GC chromosomal pattern uncharacteristic for fish. Bioinformatic analysis of the spotted gar ( Lepisosteus oculatus ) confirmed a GC compartmentalization on GC profiles of linkage groups. This indicates a rather mammalian mode of compositional organization on gar chromosomes. Gars are thus the only analyzed extant ray‐finned fishes with a GC compartmentalized genome. Since gars are cold‐blooded anamniotes, our results contradict the generally accepted hypothesis that the phylogenomic onset of GC compartmentalization occurred near the origin of amniotes. Ecophysiological findings of other authors indicate a metabolic similarity of gars with mammals. We hypothesize that gars might have undergone convergent evolution with the tetrapod lineages leading to mammals on both metabolic and genomic levels. Their metabolic adaptations might have left footprints in their compositional genome evolution, as proposed by the metabolic rate hypothesis. The genome organization described here in gars sheds new light on the compositional genome evolution in vertebrates generally and contributes to better understanding of the complexities of the mechanisms involved in this process. GRAPHICAL ABSTRACT: Gars are a unique archaic group of ray‐finned fishes. Among the few recent ray‐finned lineages, gars represent an important group that arose at the very dawn of the boom of vertebrate evolution. Gars came only recently into focus of scientists, however, the way to recognize their importance was not so straightforward, and only our study based on diversified and so far uniquely combined approach elucidated the unusual organization of their genomes. Traditional cytogenetic methods did not reveal any peculiarities, neither the analytical ultracentrifugation, a more quantitative approach, already had the potential to disclose the real genome organization. However, gars were several times omitted from this effort and remained neglected for a long time. Now, we used well combined molecular cytogenetic methods which revealed the extraordinary similarity in the AT/GC genome organization between gars and mammals. We support our findings with quantitative bioinformatics analyses. We are enthusiastic that there are still such "windows" deep into the evolutionary history of vertebrates. Better knowledge about the genome evolution and organization of these lineages bears a great potential to understand the general mechanisms shaping genome evolution not only in fishes but also in higher vertebrates including humans.