The mouse Smcx gene exhibits developmental and tissue specific variation in degree of escape from X inactivation.
The Smcx gene is the first known example of a non-pseudoautosomal X-linked gene in mouse that normally escapes X chromosome inactivation. We have analysed the kinetics of escape at different stages of development, and in adult tissues. Our results demonstrate that Smcx exhibits partial escape from X inactivation in embryos, in extraembryonic lineages where paternally imprinted X inactivation occurs and also in adult tissues. The degree of escape in different tissues is highly variable, the level of transcript from the inactive X allele representing between 20% and 70% of the active X allele. Partial escape is also seen in clones derived from haematopoietic stem cells, suggesting that partial repression of the inactive X allele is at the level of individual cells. This contrasts with classical position effect variegation (PEV), where a given gene is either active or silent in a given cell and its clonal derivatives. We discuss the implications of these results with respect to mechanisms of X inactivation and escape.
Sheardown
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Comparative Biology Group, MRC Clinical Sciences Centre, Royal Postgraduate Medical School, Hammersmith Hospital, London, UK.
Norris
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Fisher
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Brockdorff
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D000483:Alleles; D000818:Animals; D005260:Female; D008040:Genetic Linkage; D056466:Histone Demethylases; D051379:Mice; D010089:Oxidoreductases, N-Demethylating; D011506:Proteins / Q000235:genetics*; D014960:X Chromosome / Q000235:genetics*
D011506:Proteins; D056466:Histone Demethylases; C490173:Kdm5c protein, mouse; D010089:Oxidoreductases, N-Demethylating