Saturday, June 23, 2007

RNA More Important Than Genes For Evolution?

Think evolution only has to do with genes? Think again.

Scientists are now discovering than RNA plays a large role, and maybe a larger role than DNA that codes for proteins.

There are scnRNAs, snRNAs and snoRNAs. There are rasiRNAs, tasiRNAs and natsiRNAs. The piRNAs, which were discovered last summer, are abundant in developing sex cells. No male mammal, nor male fish, nor fly of either sex, would be fertile without them. Another RNA, called XIST, has the power to turn off an entire chromosome. It does so in females because they, unlike males, have two X chromosomes and would otherwise get an unhealthy double dose of many proteins. There is even a “pregnancy-induced non-coding RNA”, cutely termed PINC. New RNAs are rushing forth from laboratories so rapidly that a group called the RNA Ontology Consortium has been promised half a million dollars to prune and tend the growing thicket of RNA-tailed acronyms.

In a human, the number of different microRNAs, one of the commonest of the newly discovered sorts of RNA, may be as high as 37,000 according to Isidore Rigoutsos, IBM's genome-miner in chief. That compares with the 21,000 or so protein-encoding genes that people have.

Ronald Plasterk, of the University of Utrecht, in the Netherlands, suggests that microRNAs are important in the evolution of the human brain. In December's Nature Genetics, he compared the microRNAs encoded by chimpanzee and human genomes. About 8% of the microRNAs that are expressed in the human brain were unique to it, much more than chance and the evolutionary distance between chimps and people would predict.

Such observations suggest evolution is as much about changes in the genes for small RNAs as in the genes for proteins—and in complex creatures possibly more so. Indeed, some researchers go further. They suggest that RNA could itself provide an alternative evolutionary substrate. That is because RNA sometimes carries genetic information down the generations independently of DNA, by hitching a lift in the sex cells.
via The Economist (who by the way is now giving free access to all of their articles. Yeah!)

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