New evidence supporting the importance of a class of small RNA molecules in human evolution is reported in two papers to be published in the December 2006 issue of Nature Genetics.
MicroRNAs are small single-stranded molecules consisting of 22 nucleotides, and are thought to regulate the expression of genes by preventing their translation into proteins. Although they were discovered only recently, microRNAs have now been found in many animal and plant genomes, and are predicted to number in the hundreds, or possibly thousands, in the human genome.
Applying a new sequencing technique reported last year, Ronald Plasterk and colleagues examined the complement of microRNAs in human fetal brain and adult chimpanzee brain. They identified 447 new microRNAs, which more than doubles the diversity of known microRNAs. More than half of the human microRNAs were conserved only in chimpanzees, and not found in other organisms, suggesting a recent evolutionary origin. As many as 8% were human-specific and this specificity may signal possible roles in the evolution of the human brain.
In the second paper, Kevin Chen and Nikolaus Rajewsky used publicly available data on variation in the human genome called single-nucleotide polymorphisms - SNPs. They were interested to know whether any SNPs occurred at microRNA target sites, and, if so, whether there was any evidence that natural selection was acting to maintain these target sites. They mapped 384 SNPs to microRNA target sites, and found that the variation in these sites between individuals was less than those observed in control regions, suggesting a selective pressure to conserve the sequences of these target sites. The authors were able to infer that 85% of these microRNA target sites are likely to be functional, and suggest that SNPs at such sites might be involved in human disease.
Ronald Plasterk (Hubrecht Laboratory, Utrecht, The Netherlands)
Nikolaus Rajewsky (Max Delbrück Center for Molecular Medicine, Berlin, Germany)
Abstracts available online:
(C) Nature Genetics press release.
Message posted by: Trevor M. D'Souza