Mouse Tail Challenges Laws of Genetics.

Geneticist Minoo Rassoulzadegan at the University of Nice-Sophia Antipolis in France and colleagues discovered something very strange: an inheritance of genetic traits, mediated not by DNA, but by RNA!

A team led by developmental geneticist Minoo Rassoulzadegan of the University of Nice-Sophia Antipolis in France, made the discovery while working with mice that carry a mutant version of the Kit gene, which plays a role in coat color. Mice that are homozygous for the mutant gene--that is, animals with two copies--die shortly after birth. But heterozygotes, with one mutant and one normal Kit gene, do fine, although their feet and the tips of their tails are white rather than gray. Heterozygotes can be mated to produce offspring with two normal copies of Kit, but to the researchers' surprise, most of these progeny also had white patches, even though the mutant gene was no longer present.

The effect appears to be due to RNA. In the 25 May issue of Nature, Rassoulzadegan and her colleagues report that the tissues of the heterozygous mice and their progeny had accumulated significant amounts of abnormally small RNA molecules. Recent research has shown that abnormal RNA can interfere with the function of normal RNA--a key player in the cell's protein production machinery. Because levels of normal RNA involved in producing the Kit protein were reduced in these mice, the team hypothesized that the abnormal RNA was altering the expression of the normal Kit gene. These disruptive RNA molecules may originally come from Kit mutant fathers, who harbor them in their sperm ...


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