title: Hyperexpression of the X chromosome in both sexes results in extensive female bias of X-linked genes in the flour beetle.
abstract: A genome's ability to produce two separate sexually dimorphic phenotypes is an intriguing biological mystery. Microarray-based studies of a handful of model systems suggest that much of the mystery can be explained by sex-biased gene expression evolved in response to sexually antagonistic selection. We present the first whole-genome study of sex-biased expression in the red flour beetle, Tribolium castaneum. Tribolium is a model for the largest eukaryotic order, Coleoptera, and we show that in whole-body adults, approximately 20% of the transcriptome is differentially regulated between the sexes. Among T. castaneum, Drosophila melanogaster, and Anopheles gambiae, we identify 416 1:1:1 orthologs with conserved sex-biased expression. Overrepresented functional categories among sex-biased genes are primarily those involved in gamete production and development. The genomic distribution of sex-biased genes in T. castaneum is distinctly nonrandom, with the strongest deficit of male-biased genes on the X chromosome (9 of 793) of any species studied to date. Tribolium also shows a significant enrichment of X-linked female-biased genes (408 of 793). Our analyses suggest that the extensive female bias of Tribolium X chromosome gene expression is due to hyperexpression of X-linked genes in both males and females. We propose that the overexpression of X chromosomes in females is an evolutionary side effect of the need to dosage compensate in males and that mechanisms to reduce female X chromosome gene expression to autosomal levels are sufficient but imperfect.
authors.affiliation: Department of Biology, The University of Texas at Arlington, USA.
authors.forename: Eldon G
authors.initials: EG
authors.lastname: Prince
authors.forename: Donna
authors.initials: D
authors.lastname: Kirkland
authors.forename: Jeffery P
authors.initials: JP
authors.lastname: Demuth
mesh_terms: D000818:Animals; D000852:Anopheles / Q000235:genetics; D004303:Dosage Compensation, Genetic; D004331:Drosophila melanogaster / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D015870:Gene Expression; D020869:Gene Expression Profiling; D017344:Genes, Insect; D050172:Genes, X-Linked; D008297:Male; D008957:Models, Genetic; D012727:Sex Characteristics; D013045:Species Specificity; D014231:Tribolium / Q000235:genetics*; D014960:X Chromosome / Q000235:genetics*