title: Coexistence of Y, W, and Z sex chromosomes in Xenopus tropicalis.
abstract: Homomorphic sex chromosomes and rapid turnover of sex-determining genes can complicate establishing the sex chromosome system operating in a given species. This difficulty exists in Xenopus tropicalis, an anuran quickly becoming a relevant model for genetic, genomic, biochemical, and ecotoxicological research. Despite the recent interest attracted by this species, little is known about its sex chromosome system. Direct evidence that females are the heterogametic sex, as in the related species Xenopus laevis, has yet to be presented. Furthermore, X. laevis' sex-determining gene, DM-W, does not exist in X. tropicalis, and the sex chromosomes in the two species are not homologous. Here we identify X. tropicalis' sex chromosome system by integrating data from (i) breeding sex-reversed individuals, (ii) gynogenesis, (iii) triploids, and (iv) crosses among several strains. Our results indicate that at least three different types of sex chromosomes exist: Y, W, and Z, observed in YZ, YW, and ZZ males and in ZW and WW females. Because some combinations of parental sex chromosomes produce unisex offspring and other distorted sex ratios, understanding the sex-determination systems in X. tropicalis is critical for developing this flexible animal model for genetics and ecotoxicology.
authors.affiliation: Department of Experimental Biology, Faculty of Experimental Sciences, University of Jaén, Las Lagunillas Campus S/N, 23071 Jaén, Spain;
authors.forename: Álvaro S
authors.initials: ÁS
authors.lastname: Roco
authors.affiliation: Mid-Continent Ecology Division, Environmental Protection Agency, Duluth, MN 55804;
authors.forename: Allen W
authors.initials: AW
authors.lastname: Olmstead
authors.affiliation: Mid-Continent Ecology Division, Environmental Protection Agency, Duluth, MN 55804;
authors.forename: Sigmund J
authors.initials: SJ
authors.lastname: Degitz
authors.affiliation: Division of Developmental Biology, Medical Research Council-National Institute for Medical Research, London, NW7 1AA, United Kingdom.
authors.forename: Tosikazu
authors.initials: T
authors.lastname: Amano
authors.affiliation: Division of Developmental Biology, Medical Research Council-National Institute for Medical Research, London, NW7 1AA, United Kingdom.
authors.forename: Lyle B
authors.initials: LB
authors.lastname: Zimmerman
authors.affiliation: Department of Experimental Biology, Faculty of Experimental Sciences, University of Jaén, Las Lagunillas Campus S/N, 23071 Jaén, Spain; bullejos@ujaen.es.
authors.forename: Mónica
authors.initials: M
authors.lastname: Bullejos
mesh_terms: D000818:Animals; D005260:Female; D008297:Male; D012730:Sex Chromosomes; D019849:Sex Determination Processes; D014981:Xenopus / Q000235:genetics*
keywords: Xenopus tropicalis; gynogenesis; sex chromosomes; sex determination; sex reversal