Abstract
The field of long noncoding RNA (lncRNA) research has been rapidly advancing in recent years. Technological advancements and deep-sequencing of the transcriptome have facilitated the identification of numerous new lncRNAs, many with unusual properties, however, the function of most of these molecules is still largely unknown. Some evidence suggests that several of these lncRNAs may regulate their own transcription in cis, and that of nearby genes, by recruiting remodeling factors to local chromatin. Notably, lncRNAs are known to exist at many imprinted gene clusters. Genomic imprinting is a complex and highly regulated process resulting in the monoallelic silencing of certain genes, based on the parent-of-origin of the allele. It is thought that lncRNAs may regulate many imprinted loci, however, the mechanism by which they exert such influence is poorly understood. This review will discuss what is known about the lncRNAs of major imprinted loci, and the roles they play in the regulation of imprinting.
Highlights
Genomic imprinting is an epigenetic phenomenon, whereby differential expression of alleles occurs with respect to the parent-of-origin
It is thought to have evolved in placental mammals as a Biomolecules 2014, 4 biological/ecological mechanism for dosage compensation, whereby a conflict of interest exists over maternal investment of resources during gestation, and, dosage mediation [1,2,3]
The Imprinting Control Regions (ICRs) is considered the governing region, whose methylation marks are by definition laid down in the germline, whereas somatic Differentially Methylated Region (DMR) leading to imprinting are methylated in post-implantation embryos, and are considered secondary in the regulation hierarchy [12,16]
Summary
Genomic imprinting is an epigenetic phenomenon, whereby differential expression of alleles occurs with respect to the parent-of-origin. Imprinting is a process by which epigenetic marks are laid down at specific loci, based on the sex of the parent of origin of the chromosome, and usually leads to expression of genes from only one chromosome. In all future somatic tissue lineages, the imprinting marks are later followed by further epigenetic changes during development, resulting in a subset of genes being expressed monoallelically, from either the maternal or paternal chromosome. Most imprinted genes are found in clusters [1,14] These clusters usually feature a complex balance of both maternally- and paternally-imprinted genes in the same (often megabase-sized) locus, and many of the clusters are regulated by (and regulate) the transcriptional activity of a long noncoding RNA (lncRNA) [12]. We do not wish to disregard the importance of small noncoding RNAs (i.e., snoRNAs, miRNAs, piRNAs, etc.) in these imprinted loci [26], but for the purposes of this review, we will focus primarily on imprinted long noncoding RNAs
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