Regulation of imprinted expression by macro non-coding RNAs.

In mammals, imprinted genes are clustered and at least one gene in each imprinted cluster is a long i.e., macro non-coding (nc) RNA. Most genes in a cluster show concordant parental-specific expression but the ncRNA is the odd one out, and is expressed from the opposite parental chromosome. While reciprocal expression between imprinted macro non-coding RNAs and flanking mRNA genes is indicative of a functional role, only two of three tested macro ncRNAs have been shown to induce imprinted gene expression. The two known functional imprinted macro non-coding RNAs are both RNAPII transcripts with unusual transcriptional properties that may be functionally relevant and their analysis may shed light on the function of non-coding RNAs that have been shown to comprise the majority of the mammalian transcriptome.