title: Spontaneous germline excision of Tol1, a DNA-based transposable element naturally occurring in the medaka fish genome.
abstract: DNA-based transposable elements are ubiquitous constituents of eukaryotic genomes. Vertebrates are, however, exceptional in that most of their DNA-based elements appear to be inactivated. The Tol1 element of the medaka fish, Oryzias latipes, is one of the few elements for which copies containing an undamaged gene have been found. Spontaneous transposition of this element in somatic cells has previously been demonstrated, but there is only indirect evidence for its germline transposition. Here, we show direct evidence of spontaneous excision in the germline. Tyrosinase is the key enzyme in melanin biosynthesis. In an albino laboratory strain of medaka fish, which is homozygous for a mutant tyrosinase gene in which a Tol1 copy is inserted, we identified de novo reversion mutations related to melanin pigmentation. The gamete-based reversion rate was as high as 0.4%. The revertant fish carried the tyrosinase gene from which the Tol1 copy had been excised. We previously reported the germline transposition of Tol2, another DNA-based element that is thought to be a recent invader of the medaka fish genome. Tol1 is an ancient resident of the genome. Our results indicate that even an old element can contribute to genetic variation in the host genome as a natural mutator.
authors.affiliation: a Matsuyama High School, Higashimatsuyama 355-0018, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Watanabe
authors.forename: Hajime
authors.initials: H
authors.lastname: Koga
authors.forename: Kodai
authors.initials: K
authors.lastname: Nakamura
authors.forename: Akiko
authors.initials: A
authors.lastname: Fujita
authors.forename: Akimasa
authors.initials: A
authors.lastname: Hattori
authors.forename: Masaru
authors.initials: M
authors.lastname: Matsuda
authors.forename: Akihiko
authors.initials: A
authors.lastname: Koga
mesh_terms: D000483:Alleles; D000818:Animals; D001483:Base Sequence; D001947:Breeding; D004251:DNA Transposable Elements; D005260:Female; D056426:Genetic Loci; D016678:Genome; D005838:Genotype; D005854:Germ Cells; D008297:Male; D008969:Molecular Sequence Data; D009990:Oryzias / Q000235:genetics*; D010641:Phenotype; D017422:Sequence Analysis, DNA
chemical_list: D004251:DNA Transposable Elements
keywords: Tol1 element; excision; genetic variation; medaka fish; médaka; transposable element; variation génétique; élément Tol1; élément transposable