title: Evidence for different origin of sex chromosomes in snakes, birds, and mammals and step-wise differentiation of snake sex chromosomes.
abstract: All snake species exhibit genetic sex determination with the ZZ/ZW type of sex chromosomes. To investigate the origin and evolution of snake sex chromosomes, we constructed, by FISH, a cytogenetic map of the Japanese four-striped rat snake (Elaphe quadrivirgata) with 109 cDNA clones. Eleven of the 109 clones were localized to the Z chromosome. All human and chicken homologues of the snake Z-linked genes were located on autosomes, suggesting that the sex chromosomes of snakes, mammals, and birds were all derived from different autosomal pairs of the common ancestor. We mapped the 11 Z-linked genes of E. quadrivirgata to chromosomes of two other species, the Burmese python (Python molurus bivittatus) and the habu (Trimeresurus flavoviridis), to investigate the process of W chromosome differentiation. All and 3 of the 11 clones were localized to both the Z and W chromosomes in P. molurus and E. quadrivirgata, respectively, whereas no cDNA clones were mapped to the W chromosome in T. flavoviridis. Comparative mapping revealed that the sex chromosomes are only slightly differentiated in P. molurus, whereas they are fully differentiated in T. flavoviridis, and E. quadrivirgata is at a transitional stage of sex-chromosome differentiation. The differentiation of sex chromosomes was probably initiated from the distal region on the short arm of the protosex chromosome of the common ancestor, and then deletion and heterochromatization progressed on the sex-specific chromosome from the phylogenetically primitive boids to the more advanced viperids.
authors.affiliation: Laboratory of Animal Cytogenetics, Department of Genome Dynamics, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan.
authors.forename: Kazumi
authors.initials: K
authors.lastname: Matsubara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tarui
authors.forename: Michihisa
authors.initials: M
authors.lastname: Toriba
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Yamada
authors.forename: Chizuko
authors.initials: C
authors.lastname: Nishida-Umehara
authors.forename: Kiyokazu
authors.initials: K
authors.lastname: Agata
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Matsuda
mesh_terms: D000818:Animals; D044466:Asian People; D001483:Base Sequence; D005075:Biological Evolution; D001717:Birds / Q000235:genetics*; D003001:Cloning, Molecular; D003582:Cytogenetics; D006609:High Mobility Group Proteins / Q000235:genetics; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D008322:Mammals / Q000235:genetics*; D008969:Molecular Sequence Data; D000069497:Origin of Life; D020161:Physical Chromosome Mapping; D055758:SOX9 Transcription Factor; D012730:Sex Chromosomes / Q000235:genetics*; D012911:Snakes / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics
chemical_list: C110547:DMRT1 protein; D006609:High Mobility Group Proteins; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; D014157:Transcription Factors