Deep ancestry of mammalian X chromosome revealed by comparison with the basal tetrapod Xenopus tropicalis

作者：Macha Jaroslav; Teichmanova Radka; Sater Amy K; Wells Dan E; Tlapakova Tereza; Zimmerman Lyle B^*; Krylov Vladimir

来源：BMC Genomics, 2012, 13: 315.

DOI：10.1186/1471-2164-13-315

• X chromosome
• Evolution
• Xenopus
• Synteny
• Genome
• TAG

Background: The X and Y sex chromosomes are conspicuous features of placental mammal genomes. Mammalian sex chromosomes arose from an ordinary pair of autosomes after the proto-Y acquired a male-determining gene and degenerated due to suppression of X-Y recombination. Analysis of earlier steps in X chromosome evolution has been hampered by the long interval between the origins of teleost and amniote lineages as well as scarcity of X chromosome orthologs in incomplete avian genome assemblies. %26lt;br%26gt;Results: This study clarifies the genesis and remodelling of the Eutherian X chromosome by using a combination of sequence analysis, meiotic map information, and cytogenetic localization to compare amniote genome organization with that of the amphibian Xenopus tropicalis. Nearly all orthologs of human X genes localize to X. tropicalis chromosomes 2 and 8, consistent with an ancestral X-conserved region and a single X-added region precursor. This finding contradicts a previous hypothesis of three evolutionary strata in this region. Homologies between human, opossum, chicken and frog chromosomes suggest a single X-added region predecessor in therian mammals, corresponding to opossum chromosomes 4 and 7. A more ancient X-added ancestral region, currently extant as a major part of chicken chromosome 1, is likely to have been present in the progenitor of synapsids and sauropsids. Analysis of X chromosome gene content emphasizes conservation of single protein coding genes and the role of tandem arrays in formation of novel genes. %26lt;br%26gt;Conclusions: Chromosomal regions orthologous to Therian X chromosomes have been located in the genome of the frog X. tropicalis. These X chromosome ancestral components experienced a series of fusion and breakage events to give rise to avian autosomes and mammalian sex chromosomes. The early branching tetrapod X. tropicalis%26apos; simple diploid genome and robust synteny to amniotes greatly enhances studies of vertebrate chromosome evolution.

• 出版日期2012-7-16
• 单位河北医科大学