Not AvailableUsually, most of the genes are biallelically expressed but imprinted gene exhibit monoallelic expression
based on their parental origin. Genomic imprinting exhibit differences in control between flowering
plants and mammals, for instance, imprinted gene are specifically activated by demethylation, rather
than targeted for silencing in plants and imprinted gene expression in plant which occur in endosperm.
It also displays sexual dimorphism like differential timing in imprint establishment and RNA based
silencing mechanism in paternally repressed imprinted gene. Within imprinted regions, the unusual
occurrence and distribution of various types of repetitive elements may act as genomic imprinting
signatures. Imprinting regulation probably at many loci involves insulator protein dependent and
higher-order chromatin interaction, and/or non-coding RNAs mediated mechanisms. However, placentaspecific
imprinting involves repressive histone modifications and non-coding RNAs. The higher-order
chromatin interaction involves differentially methylated domains (DMDs) exhibiting sex-specific
methylation that act as scaffold for imprinting, regulate allelic-specific imprinted gene expression. The
paternally methylated differentially methylated regions (DMRs) contain less CpGs than the maternally
methylated DMRs. The non-coding RNAs mediated mechanisms include C/D RNA and microRNA, which
are invovled in RNA-guided post-transcriptional RNA modifications and RNA-mediated gene silencing,
respectively. The maintenance and reprogramming of imprinting are not significantly affected by
reduced expression of Dicer1 and the evolution of imprinting might be related to acquisition of DNMT3L
(de novo methyltransferase 3L) by a common ancestor of eutherians and marsupials. The common
feature among diverse imprinting control elements and evolutionary significance of imprinting need to
be identified.Not Availabl
