Identification of a cluster of X-linked imprinted genes in mice

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Abstract
Complete or partial monosomy with respect to the X chromosome is the genetic basis of Turner syndrome in human females. Individuals with Turner syndrome have a spectrum of anatomical, physiological and behavioral phenotypes with expressivity dependent on the extent of monosomy and the parental origin of the single X1. Parent-of-origin influences on social cognition in Turner syndrome might be due to the presence of imprinted genes on the X2. Imprinting of X-linked genes has also been implicated in the male prevalence of autistic spectrum disorders3, in male sexual orientation4,5 and in the developmental delay of XO mouse embryos6,7,8. The only molecular evidence for X-chromosome imprinting, however, concerns X-chromosome inactivation in specific circumstances9,10 and does not account for these phenotypes. Using a mouse model for Turner syndrome, we searched for locus-specific imprinting of X-linked genes in developing brain. We identified a cluster of X-linked genes containing at least three genes that show transcriptional repression of paternal alleles. Imprinting of these three genes, Xlr3b, Xlr4b and Xlr4c, is independent of X-chromosome inactivation and has a dynamic and complex pattern of tissue and stage specificity.