In contrast to mammals and birds,fish display an amazing diversity of genetic sex determination systems,with frequent changes during evolution possibly associated with the emergence of new sex chromosomes and sex-dete...In contrast to mammals and birds,fish display an amazing diversity of genetic sex determination systems,with frequent changes during evolution possibly associated with the emergence of new sex chromosomes and sex-determining genes.To better understand the molecular and evolutionary mechanisms driving this diversity,several fish models are studied in parallel.Besides the medaka(Oryzias latipes Temminck and Schlegel,1846)for which the master sex-determination gene has been identified,one of the most advanced models for studying sex determination is the Southern platyfish(Xiphophorus maculatus,Günther 1966).Xiphophorus maculatus belongs to the Poeciliids,a family of live-bearing freshwater fish,including platyfish,swordtails and guppies that perfectly illustrates the diversity of genetic sex-determination mechanisms observed in teleosts.For X.maculatus,bacterial artificial chro-mosome contigs covering the sex-determination region of the X and Y sex chromosomes have been constructed.Initial molecular analysis demonstrated that the sex-determination region is very unstable and frequently undergoes duplications,deletions,inversions and other rearrangements.Eleven gene candidates linked to the master sex-determining gene have been identified,some of them corresponding to pseudogenes.All putative genes are present on both the X and the Y chromosomes,suggesting a poor degree of differentiation and a young evolutionary age for platyfish sex chromosomes.When compared with other fish and tetrapod genomes,syntenies were detected only with autosomes.This observation supports an independent origin of sex chromosomes,not only in different vertebrate lineages but also between different fish species.展开更多
A consensus sequence, encoding a putative DNA polymerase type B derived from a Polinton transposon, was assembled from the sex determination region of Xiphophorus maculatus. This predicted protein, which is 1,158 aa i...A consensus sequence, encoding a putative DNA polymerase type B derived from a Polinton transposon, was assembled from the sex determination region of Xiphophorus maculatus. This predicted protein, which is 1,158 aa in length, contains a DNAA_pol_B_2 domain and a DTDS motif. The DNA polymerase type B gene has about 10 copies in the haploid X. maculatus genome with one Y-specific copy. Interestingly, it has specific copies on the W chromosome in the X. maculatus Usumacinta strain （sex determination with female het- erogamety）, which represent new markers for this type of sex chromosome in platyfish. This marker with W- and Y-specific copies suggests relationship between different types of gonosomes and allows comparing male and female heterogameties in the platyfish. Further molecular analysis of the DNA polymerase type B gene in X. maculatus will shed new light on the evolution of sex chromosomes in platyfish.展开更多
文摘In contrast to mammals and birds,fish display an amazing diversity of genetic sex determination systems,with frequent changes during evolution possibly associated with the emergence of new sex chromosomes and sex-determining genes.To better understand the molecular and evolutionary mechanisms driving this diversity,several fish models are studied in parallel.Besides the medaka(Oryzias latipes Temminck and Schlegel,1846)for which the master sex-determination gene has been identified,one of the most advanced models for studying sex determination is the Southern platyfish(Xiphophorus maculatus,Günther 1966).Xiphophorus maculatus belongs to the Poeciliids,a family of live-bearing freshwater fish,including platyfish,swordtails and guppies that perfectly illustrates the diversity of genetic sex-determination mechanisms observed in teleosts.For X.maculatus,bacterial artificial chro-mosome contigs covering the sex-determination region of the X and Y sex chromosomes have been constructed.Initial molecular analysis demonstrated that the sex-determination region is very unstable and frequently undergoes duplications,deletions,inversions and other rearrangements.Eleven gene candidates linked to the master sex-determining gene have been identified,some of them corresponding to pseudogenes.All putative genes are present on both the X and the Y chromosomes,suggesting a poor degree of differentiation and a young evolutionary age for platyfish sex chromosomes.When compared with other fish and tetrapod genomes,syntenies were detected only with autosomes.This observation supports an independent origin of sex chromosomes,not only in different vertebrate lineages but also between different fish species.
基金supported by the grants from the Biofuture Programme of the German Federal Ministry for Education and Research (BMBF,to JNV),the French Research Agency (ANR to JNV)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,the Ministry of Education of China (to QZ)
文摘A consensus sequence, encoding a putative DNA polymerase type B derived from a Polinton transposon, was assembled from the sex determination region of Xiphophorus maculatus. This predicted protein, which is 1,158 aa in length, contains a DNAA_pol_B_2 domain and a DTDS motif. The DNA polymerase type B gene has about 10 copies in the haploid X. maculatus genome with one Y-specific copy. Interestingly, it has specific copies on the W chromosome in the X. maculatus Usumacinta strain （sex determination with female het- erogamety）, which represent new markers for this type of sex chromosome in platyfish. This marker with W- and Y-specific copies suggests relationship between different types of gonosomes and allows comparing male and female heterogameties in the platyfish. Further molecular analysis of the DNA polymerase type B gene in X. maculatus will shed new light on the evolution of sex chromosomes in platyfish.
