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

BMC Genomics

Research Article

Amy K Sater¹  Dan E Wells¹  Jaroslav Mácha²  Tereza Tlapáková²  Radka Teichmanová²  Vladimír Krylov²  Lyle B Zimmerman³ 

[1] Department of Biology and Biochemistry, University of Houston, 77204-5001, Houston, TX, USA;Department of Cell Biology, Faculty of Science, Charles University in Prague, Vinicna 7, Prague 2, Czech Republic;Division of Developmental Biology, MRC-National Institute for Medical Research, NW7 1AA, Mill HillLondon, UK;

关键词: X chromosome;    Evolution;    Xenopus;    Synteny;    Genome;    TAG;   

DOI  :  10.1186/1471-2164-13-315

 received in 2012-01-30, accepted in 2012-06-25,  发布年份 2012

来源: Springer

【 摘 要 】

BackgroundThe 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.ResultsThis 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.ConclusionsChromosomal 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’ simple diploid genome and robust synteny to amniotes greatly enhances studies of vertebrate chromosome evolution.

【 授权许可】

Unknown   
© Mácha et al.; licensee BioMed Central Ltd. 2012. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.