New evidence for epigenetic inheritance
- From: "Peter F" <19eimc_minus19@xxxxxxxxxxxxxx>
- Date: Fri, 26 May 2006 13:47:26 -0400 (EDT)
http://www.sciam.com/article.cfm?chanID=sa003&articleID=0002F1FB-D535-1474-953583414B7F0000From
Mouse Finding Violates Laws of Heredity
DNA has long been considered the sole arbiter of heredity. New research
seems to show, however, that its lesser known cousin, RNA--previously
thought only to facilitate the creation of proteins as dictated by the
genetic code--may itself pass traits down through the generations.
Fifty years ago, researchers observed that the factors controlling the
amount of purple coloring in certain corn kernels deviated from the accepted
laws of genetics. Genetic variants that should have been bred out could
sometimes exert their empurpling effect in subsequent generations. Dubbed
paramutation, the phenomenon remained unexplained.
In experiments with mutant mice, Minoo Rassoulzadegan of Inserm in France
and his colleagues observed a similar phenomenon. A mutation in the Kit gene
is known to produce white patches of fur on the toes and tails of brown
mice. The researchers bred together mice that each carried one normal copy
of the gene and one aberrant copy--that is, they were heterozygous. Mice
that inherit two normal copies of the gene should not exhibit this coloring.
But oddly enough, the team found that a large percentage of the resulting
mice in their study that inherited only normal copies of the gene from their
heterozygous parents did in fact have the white spots.
Searching for an explanation, the scientists found that the mutant mice bore
unusually low levels of regular RNA interspersed with unusually large
versions of the messenger molecule. Further, they noticed that this RNA
found its way into mouse sperm. And when they injected the RNA into
developing embryos it produced the telltale patches in nearly 50 percent of
the offspring, who in turn passed the trait along to their offspring.
Control mice occasionally exhibited white spots as well, though they rarely
passed the trait to subsequent generations.
The exact mechanism by which RNA transmits the spotting trait to progeny in
the absence of the gene that causes spotting in the parent remains
mysterious. But the finding does challenge the existing understanding of
genetics, and it may have implications for humans. In a commentary
accompanying the report, Paul Soloway of Cornell University remarks: "A
particularly intriguing possibility is that such RNAs regulate other
non-genetic modes of inheritance, such as metabolic or behavioral
imprinting."
The research and commentary appear in today's Nature. --David Biello
.
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