Article: Mendel's Laws: Foiled Again

Mendel's Laws: Foiled Again
By Michael Balter

24 May 2006

Pity poor Gregor Mendel. During most of the 20th century, the laws of
inheritance discovered by this modest priest and gardener ruled genetics.
But over the past decade, researchers have spotted numerous violations of
Mendel's laws. These exceptions, called epigenetic effects, are currently
under intense study by biologists, who are searching for their underlying
mechanisms (ScienceNOW, 12 April). A new study suggests that at least one of
the perpetrators of these anti-Mendelian acts is none other than RNA,
previously thought to be a loyal cog in the machinery of conventional
genetics.

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 (ScienceNOW, 9 September 2002).

Full Text at Science
http://sciencenow.sciencemag.org/cgi/content/full/2006/524/1?etoc

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Robert Karl Stonjek


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