title: Sex-biased gene expression and evolution of the x chromosome in nematodes.
abstract: Studies of X chromosome evolution in various organisms have indicated that sex-biased genes are nonrandomly distributed between the X and autosomes. Here, to extend these studies to nematodes, we annotated and analyzed X chromosome gene content in four Caenorhabditis species and in Pristionchus pacificus. Our gene expression analyses comparing young adult male and female mRNA-seq data indicate that, in general, nematode X chromosomes are enriched for genes with high female-biased expression and depleted of genes with high male-biased expression. Genes with low sex-biased expression do not show the same trend of X chromosome enrichment and depletion. Combined with the observation that highly sex-biased genes are primarily expressed in the gonad, differential distribution of sex-biased genes reflects differences in evolutionary pressures linked to tissue-specific regulation of X chromosome transcription. Our data also indicate that X dosage imbalance between males (XO) and females (XX) is influential in shaping both expression and gene content of the X chromosome. Predicted upregulation of the single male X to match autosomal transcription (Ohno's hypothesis) is supported by our observation that overall transcript levels from the X and autosomes are similar for highly expressed genes. However, comparison of differentially located one-to-one orthologs between C. elegans and P. pacificus indicates lower expression of X-linked orthologs, arguing against X upregulation. These contradicting observations may be reconciled if X upregulation is not a global mechanism but instead acts locally on a subset of tissues and X-linked genes that are dosage sensitive.
authors.affiliation: Department of Biology, Center for Genomics and Systems Biology, New York University, New York, New York 10003.
authors.forename: Sarah Elizabeth
authors.initials: SE
authors.lastname: Albritton
authors.affiliation: Department of Biology, Center for Genomics and Systems Biology, New York University, New York, New York 10003.
authors.forename: Anna-Lena
authors.initials: AL
authors.lastname: Kranz
authors.affiliation: Department of Biology, Center for Genomics and Systems Biology, New York University, New York, New York 10003.
authors.forename: Prashant
authors.initials: P
authors.lastname: Rao
authors.affiliation: Department of Biology, Center for Genomics and Systems Biology, New York University, New York, New York 10003.
authors.forename: Maxwell
authors.initials: M
authors.lastname: Kramer
authors.affiliation: Max Planck Institute for Biology of Ageing, D-50931 Cologne, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Dieterich
authors.affiliation: Department of Biology, Center for Genomics and Systems Biology, New York University, New York, New York 10003 se71@nyu.edu.
authors.forename: Sevinç
authors.initials: S
authors.lastname: Ercan
mesh_terms: D000818:Animals; D002107:Caenorhabditis / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D018628:Gene Dosage; D005786:Gene Expression Regulation; D017238:Genes, Helminth; D050172:Genes, X-Linked; D006066:Gonads / Q000378:metabolism; D057895:Haploinsufficiency / Q000235:genetics; D057850:Hermaphroditic Organisms / Q000235:genetics; D008297:Male; D009348:Nematoda / Q000235:genetics*; D009928:Organ Specificity / Q000235:genetics; D010802:Phylogeny; D063507:Sexism; D013045:Species Specificity; D014960:X Chromosome / Q000235:genetics*
keywords: X chromosome evolution; dosage compensation; genomics; nematode; sex-biased gene expression