Methylation profile of genes on the human X chromosome

X chromosome inactivation occurs in female mammals for the purpose of equalisation of dosage of X linked genes between the two sexes. In eutherian mammals, one of the two copies of the X chromosome present in female individuals is silenced. Epigenetic modifications of both DNA and histones have been implicated to play a crucial role in this inactivation phenomenon. In this work, we have employed a novel method published earlier by us, to assess the DNA methylation levels of genes on the inactive X chromosome in the human system. We have used genomic DNA from cells with the following karyotype namely, 47,XXX and 45,X to compare methylation levels from the active and inactive X. We report differential methylation of genes from the active and the inactive X chromosome with higher number of methylated genes being present on the inactive X chromosome. Our work has also led to identification of motifs that show a significant similarity to microRNA sequences which are enriched in methylated regions specific to the inactive X.