title: Demasculinization of the Anopheles gambiae X chromosome.
abstract: BACKGROUND
  In a number of organisms sex-biased genes are non-randomly distributed between autosomes and the shared sex chromosome X (or Z). Studies on Anopheles gambiae have produced conflicting results regarding the underrepresentation of male-biased genes on the X chromosome and it is unclear to what extent sexual antagonism, dosage compensation or X-inactivation in the male germline, the evolutionary forces that have been suggested to affect the chromosomal distribution of sex-biased genes, are operational in Anopheles.
  
  
  RESULTS
  We performed a meta-analysis of sex-biased gene expression in Anopheles gambiae which provides evidence for a general underrepresentation of male-biased genes on the X-chromosome that increased in significance with the observed degree of sex-bias. A phylogenomic comparison between Drosophila melanogaster, Aedes aegypti and Culex quinquefasciatus also indicates that the Anopheles X chromosome strongly disfavours the evolutionary conservation of male-biased expression and that novel male-biased genes are more likely to arise on autosomes. Finally, we demonstrate experimentally that transgenes situated on the Anopheles gambiae X chromosome are transcriptionally silenced in the male germline.
  
  
  CONCLUSIONS
  The data presented here support the hypothesis that the observed demasculinization of the Anopheles X chromosome is driven by X-chromosome inactivation in the male germline and by sexual antagonism. The demasculinization appears to be the consequence of a loss of male-biased expression, rather than a failure in the establishment or the extinction of male-biased genes.
authors.affiliation: Imperial College London, Department of Life Sciences, Imperial College Road, London, SW7 2AZ, UK.
authors.forename: Kalle
authors.initials: K
authors.lastname: Magnusson
authors.forename: Gareth J
authors.initials: GJ
authors.lastname: Lycett
authors.forename: Antonio M
authors.initials: AM
authors.lastname: Mendes
authors.forename: Amy
authors.initials: A
authors.lastname: Lynd
authors.forename: Philippos-Aris
authors.initials: PA
authors.lastname: Papathanos
authors.forename: Andrea
authors.initials: A
authors.lastname: Crisanti
authors.forename: Nikolai
authors.initials: N
authors.lastname: Windbichler
mesh_terms: D000818:Animals; D000852:Anopheles / Q000235:genetics*; D003465:Culex / Q000235:genetics; D004331:Drosophila melanogaster / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D020869:Gene Expression Profiling; D020868:Gene Silencing; D017344:Genes, Insect; D023281:Genomics; D005854:Germ Cells / Q000378:metabolism; D008297:Male; D020411:Oligonucleotide Array Sequence Analysis; D010802:Phylogeny; D019076:Transgenes; D014960:X Chromosome / Q000235:genetics*; D049951:X Chromosome Inactivation