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MicroRNAs Make Big Appearance
By Kate Dalke

A few years ago no one had even heard of microRNAs. Now, scientists have shown that there are at least 200 microRNA genes in the human genome.

What microRNAs do in humans is unclear, but some are known to regulate the expression of other genes and control development.

Some researchers think that microRNAs help give higher organisms their complexity by regulating the development of cells. These genes have not yet been found in yeast and other single-cell organisms.

In this study, the researchers developed a computer program to identify genes that code for microRNAs in the human genome based on two criteria: their structures and their presence in the genomes of mice and pufferfish. MicroRNAs are highly conserved among related species like mouse, human and pufferfish.

“Having all three genomes was essential for this study,” says Christopher Burge of the Massachusetts Institute of Technology in Cambridge. He co-led the research with David Bartel of MIT and the Whitehead Institute for Biomedical Research, also in Cambridge.

The new study is one of a handful of projects trying to identify genes that code for microRNAs.

“The big question we’d all like to answer is what these genes do,” says Burge. His team reported the identities of close to 200 human microRNAs in Science.

“This study is important because it provides an estimate of the total number of microRNA genes in vertebrate genomes,” says Victor Ambros of Dartmouth Medical School in Hanover, New Hampshire, who led one of the teams to first identify microRNAs.

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Lim, L.P. et al. Vertebrate microRNA genes. Science 299, 1540 (March 7, 2003).

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