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

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 X. Parent-of-origin influences on social cognition in Turner syndrome might be due to the presence of imprinted genes on the X. Imprinting of X-linked genes has also been implicated in the male prevalence of autistic spectrum disorders, in male sexual orientation and in the developmental delay of XO mouse embryos. The only molecular evidence for X-chromosome imprinting, however, concerns X-chromosome inactivation in specific circumstances 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.

Wnt pathway anomalies in developing amygdalae of Turner syndrome-like mice.

Certain neurobehavioral deficiencies associated with Turner Syndrome have been attributed to brain volumetric abnormalities, particularly of the amygdala. Haplo-insufficiency of a non-dosage compensated gene or genes on the X chromosome has been hypothesized to be the cause of the neuroanatomical defect. We examined gene expression levels of 6,628 genes in developing amygdalae of late-stage embryos of a mouse model for Turner Syndrome. In total, 161 genes show significant differences in expression level between TS and normal female amygdala. In silico pathway analysis of both X-linked and autosomal mis-regulated genes suggests that modulation of Wnt signaling is a critical factor in the normal growth and development of the amygdala.