ncRNA
Non-coding RNA (ncRNA) genes produce functional RNA molecules rather than encoding proteins.
Non-coding RNAs refers to transcripts expressed and processed in the nucleus much like any protein coding gene, but lacking an open reading frame and often transcribed antisense to bona fide protein coding genes.
In mammals, these types of transcripts are highly coincident with allele-specific silencing of imprinted genes and have a proven role in dosage compensation via X-inactivation.
Mechanisms such as RNA interference may have deep phylogenetic roots, but their relevance to imprinting and X-inactivation in mammals has not been proven.
The remarkable diversity of non-coding transcription associated with parent-of-origin directed gene silencing hints at an equally diverse assortment of mechanisms.
The significance of noncoding RNAs in processes such as chromatin dynamics and gene silencing has received increased attention over the last years, especially following the unmasking of the large group of small regulatory microRNAs.
Noncoding RNAs have long been known to regulate fundamental processes, such as the function of Xist in the initiation of X-chromosome inactivation; also, processes such as Polycomb-mediated silencing and the association of HP1 to chromatin have been reported to involve an RNA moiety.
In addition, noncoding antisense RNAs are involved in processes of imprinting, suggesting a pattern in which antisense RNA can induce transcriptional silencing as a means of gene regulation in normal and disease cells.
This theory was recently supported for the -globin gene from a patient carrying a deletion that juxtaposes the highly expressed LUC7L gene in antisense to beta-globin.
Importantly, the antisense RNA induces transcriptional silencing of the -globin gene associated with methylation of the CpG island at the beta-globin gene. Also, data from fission yeast implicate the RNAi machinery in the initiation and maintenance of heterochromatin.
References
Pang KC, Frith MC, Mattick JS. Rapid evolution of noncoding RNAs: lack of conservation does not mean lack of function. Trends Genet. 2006 Jan;22(1):1-5. PMID: 16290135
Huttenhofer A, Schattner P, Polacek N. Non-coding RNAs: hope or hype? Trends Genet. 2005 May;21(5):289-97. PMID: 15851066
O?Neill MJ. The influence of non-coding RNAs on allele-specific gene expression in mammals. Hum Mol Genet. 2005 Apr 15;14 Spec No 1:R113-20. PMID: 15809263