During early embryogenesis, epigenetic marks (e.g. DNA methylation) are added to clusters of imprinted genes to direct their subsequent expression from one parental allele. Lewis, Green and co-workers have been analysing the epigenetic modifications to, and the allele-specific expression patterns of,the genes in the mouse Kcnq1 imprinted domain and now describe the epigenetic dynamics of this cluster (see p. 4203). The Kcnq1 domain contains one paternally expressed gene (the non-coding antisense transcript Kcnq1ot1), several nearby genes that are paternally repressed in all lineages by this transcript and other more distant genes that are paternally repressed in only placental lineages. The researchers report that Kcnq1ot1 silences the ubiquitously imprinted genes by the blastocyst stage - a similar timing to that of imprinted X inactivation. By contrast, the genes that are imprinted only in the placenta,although also regulated by Kcnq1ot1, are inactivated later during trophoblast differentiation. The researchers conclude that epigenetic gene silencing by non-coding RNA may depend on the distance from the RNA and on lineage- and differentiation-specific factors.

© 2006.
2006