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Nat Genet. 2010 Dec;42(12):1043-7. doi: 10.1038/ng.711.

RNA sequencing shows no dosage compensation of the active X-chromosome.

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State Key Laboratory of Biocontrol, College of Life Sciences, Sun Yat-sen University, Guangzhou, China.


Mammalian cells from both sexes typically contain one active X chromosome but two sets of autosomes. It has previously been hypothesized that X-linked genes are expressed at twice the level of autosomal genes per active allele to balance the gene dose between the X chromosome and autosomes (termed 'Ohno's hypothesis'). This hypothesis was supported by the observation that microarray-based gene expression levels were indistinguishable between one X chromosome and two autosomes (the X to two autosomes ratio (X:AA) ~1). Here we show that RNA sequencing (RNA-Seq) is more sensitive than microarray and that RNA-Seq data reveal an X:AA ratio of ~0.5 in human and mouse. In Caenorhabditis elegans hermaphrodites, the X:AA ratio reduces progressively from ~1 in larvae to ~0.5 in adults. Proteomic data are consistent with the RNA-Seq results and further suggest the lack of X upregulation at the protein level. Together, our findings reject Ohno’s hypothesis, necessitating a major revision of the current model of dosage compensation in the evolution of sex chromosomes.

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