New regulatory elements within the human genome

13 October 2010

Despite amazing progress in the analysis of the genome, the role of as much as 95 percent of human DNA is still unclear; the genes or coding regions represent only a very small proportion of the total sequence. Some of the rest specifies the production of long non-coding RNA (ncRNA). Now a new study recently published in Cell sheds new light on the distribution of nc-RNA molecules, and suggests a potential role in the regulation of gene expression.
 
The researchers mapped the ncRNA sites within the genome using GENCODE, a database that annotates the human genome with currently available scientific evidence. They found 3,000 ncRNA sites within the genome and estimated that there could be a total of 10 to 12,000 such sequences in human DNA. Interestingly, this is comparable with about 20,000 genes known to encode proteins [Ørom UA et al. (2010) Cell 143(1):46-58].
 
The ncRNA sites were mostly in close proximity to genes critical for cell development and differentiation, and the long ncRNAs themselves were found to be present in a variety of cell types.  Depletion of a number of ncRNAs led to decreased expression of their neighbouring protein-coding genes, revealing a possible role for ncRNAs in regulating gene expression, acting as gene enhancer elements - short regions of DNA that can promote gene transcription. The concept of gene enhancers has been known for decades but there has been no consensus how they might work; improved understanding may reveal new therapeutic avenues for conditions such as cancer.

The results of this study add to the ever-growing body of evidence that the classic ‘central dogma’ of molecular biology is incomplete. This original dogma set out a unidirectional flow of information from DNA transcribed into RNA, then translated into proteins. In recent years, however, studies have shown that a significant portion of transcribed RNA molecules are not translated into proteins, but play various regulatory roles in the cell. 

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