title: Rapid evolution of cancer/testis genes on the X chromosome.
abstract: BACKGROUND
  Cancer/testis (CT) genes are normally expressed only in germ cells, but can be activated in the cancer state. This unusual property, together with the finding that many CT proteins elicit an antigenic response in cancer patients, has established a role for this class of genes as targets in immunotherapy regimes. Many families of CT genes have been identified in the human genome, but their biological function for the most part remains unclear. While it has been shown that some CT genes are under diversifying selection, this question has not been addressed before for the class as a whole.
  
  
  RESULTS
  To shed more light on this interesting group of genes, we exploited the generation of a draft chimpanzee (Pan troglodytes) genomic sequence to examine CT genes in an organism that is closely related to human, and generated a high-quality, manually curated set of human:chimpanzee CT gene alignments. We find that the chimpanzee genome contains homologues to most of the human CT families, and that the genes are located on the same chromosome and at a similar copy number to those in human. Comparison of putative human:chimpanzee orthologues indicates that CT genes located on chromosome X are diverging faster and are undergoing stronger diversifying selection than those on the autosomes or than a set of control genes on either chromosome X or autosomes.
  
  
  CONCLUSIONS
  Given their high level of diversifying selection, we suggest that CT genes are primarily responsible for the observed rapid evolution of protein-coding genes on the X chromosome.
authors.affiliation: Ludwig Institute for Cancer Research and Swiss Institute of Bioinformatics, Lausanne, Switzerland. brian.stevenson@licr.org
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Stevenson
authors.forename: Christian
authors.initials: C
authors.lastname: Iseli
authors.forename: Sumir
authors.initials: S
authors.lastname: Panji
authors.forename: Monique
authors.initials: M
authors.lastname: Zahn-Zabal
authors.forename: Winston
authors.initials: W
authors.lastname: Hide
authors.forename: Lloyd J
authors.initials: LJ
authors.lastname: Old
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Simpson
authors.forename: C Victor
authors.initials: CV
authors.lastname: Jongeneel
mesh_terms: D000818:Animals; D041321:Chromosomes, Human, X / Q000235:genetics*; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D052138:Genes, Neoplasm / Q000235:genetics*; D015894:Genome, Human; D006801:Humans; D007167:Immunotherapy; D008297:Male; D002679:Pan troglodytes; D016133:Polymerase Chain Reaction; D016415:Sequence Alignment; D013737:Testis