title: Transposable elements and early evolution of sex chromosomes in fish.
abstract: In many organisms, the sex chromosome pair can be recognized due to heteromorphy; the Y and W chromosomes have often lost many genes due to the absence of recombination during meiosis and are frequently heterochromatic. Repetitive sequences are found at a high proportion on such heterochromatic sex chromosomes and the evolution and emergence of sex chromosomes has been connected to the dynamics of repeats and transposable elements. With an amazing plasticity of sex determination mechanisms and numerous instances of independent emergence of novel sex chromosomes, fish represent an excellent lineage to investigate the early stages of sex chromosome differentiation, where sex chromosomes often are homomorphic and not heterochromatic. We have analyzed the composition, distribution, and relative age of TEs from available sex chromosome sequences of seven teleost fish. We observed recent bursts of TEs and simple repeat accumulations around young sex determination loci. More strikingly, we detected transposable element (TE) amplifications not only on the sex determination regions of the Y and W sex chromosomes, but also on the corresponding regions of the X and Z chromosomes. In one species, we also clearly demonstrated that the observed TE-rich sex determination locus originated from a TE-poor genomic region, strengthening the link between TE accumulation and emergence of the sex determination locus. Altogether, our results highlight the role of TEs in the initial steps of differentiation and evolution of sex chromosomes.
authors.affiliation: Institut de Génomique Fonctionnelle de Lyon, CNRS UMR5242, Ecole Normale Supérieure de Lyon, Lyon, France.|Department of Genetics, University of Georgia, Athens, GA, USA.
authors.forename: Domitille
authors.initials: D
authors.lastname: Chalopin
authors.affiliation: Institut de Génomique Fonctionnelle de Lyon, CNRS UMR5242, Ecole Normale Supérieure de Lyon, Lyon, France.
authors.forename: Jean-Nicolas
authors.initials: JN
authors.lastname: Volff
authors.affiliation: Institut de Génomique Fonctionnelle de Lyon, CNRS UMR5242, Ecole Normale Supérieure de Lyon, Lyon, France.
authors.forename: Delphine
authors.initials: D
authors.lastname: Galiana
authors.affiliation: INRA, Fish Physiology and Genomics (UR1037), Campus de Beaulieu, Rennes, France.|Department of Organismal Biology, Uppsala University, Uppsala, Sweden.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Anderson
authors.affiliation: Department Physiological Chemistry, Biozentrum, University of Wuerzburg, and Comprehensive Cancer Center Mainfranken, University Clinic Wuerzburg, Wuerzburg, Germany. phch1@biozentrum.uni-wuerzburg.de.
authors.forename: Manfred
authors.initials: M
authors.lastname: Schartl
mesh_terms: D000818:Animals; D002874:Chromosome Mapping; D004251:DNA Transposable Elements; D066264:Datasets as Topic; D019143:Evolution, Molecular; D005399:Fishes / Q000235:genetics*; D014644:Genetic Variation; D016678:Genome; D023281:Genomics; D012730:Sex Chromosomes; D019849:Sex Determination Processes / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements
keywords: Fish; Sex chromosomes; Transposable elements