High expression of the mammalian X chromosome in brain.
Divergence between the sex chromosomes has led to loss and differentiation of Y-linked genes and haplo-insufficiency for X-linked genes in males. A mechanism of dosage compensation, for which we recently found evidence in mammals, evolved to restore a balanced expression of the genome by doubling the transcriptional output from the X chromosome. X inactivation would then serve to avoid hyper-transcription of X-linked genes in females by silencing one X chromosome. We also found that, compared to the rest of the genome, the X chromosome contains an excess of genes highly expressed in brain tissues. The exceptionally important role of the X chromosome in brain function, evident from the prevalence of X-linked forms of mental retardation, is discussed in view of sex chromosome regulation and evolution and sexual reproduction.
Nguyen
Di Kim
DK
Department of Pathology, University of Washington, Seattle, WA 98195, USA.
Disteche
Christine M
CM
D000818:Animals; D001921:Brain / Q000196:embryology* / Q000254:growth & development / Q000378:metabolism; D001923:Brain Chemistry / Q000235:genetics*; D004303:Dosage Compensation, Genetic / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D040181:Genetic Diseases, X-Linked / Q000235:genetics; D006801:Humans; D008297:Male; D008322:Mammals / Q000235:genetics*; D012733:Sex Differentiation / Q000235:genetics; D014960:X Chromosome / Q000235:genetics*; D049951:X Chromosome Inactivation / Q000235:genetics; D014998:Y Chromosome / Q000235:genetics