Brussels, 26 May 2006
French researchers have discovered that RNA, cousin of the more familiar DNA, has a role in the transfer of genetic information, completely changing the way in which we think about genetic inheritance.
In tests on mice, the team from the French Institute of Health and Medical Research (Inserm) and the University of Nice-Sophia Antipolis found that specific genetic information could be passed to new generations, even when the corresponding DNA was absent.
The tests were simple - on mice with and without spots on their tails and feet. The researchers knew that the genetic information for this mutation was carried in a specific gene, known as Kit. The mutant Kit gene is dominant, so the spots can be seen when there is one mutant and one normal Kit copy.
According to genetics, there are three possible combinations of mouse - with two mutant genes, which should be spotty, with one mutant and one normal gene - these should also be spotty, and with two normal genes - these should not be spotty.
However, when the researchers, led by Minoo Rassoulzadegan, bred the mice, they found that the offspring with two normal genes - which ought to display no spots - did show spots after all.
This result runs against all current knowledge in genetics. The only explanation the researchers could find to explain this lay in RNA. The mutant Kit gene is known to produce large quantities of RNA. RNA was until now considered to be simply a kind of intermediary between DNA and proteins. DNA produces RNA, which in turn is used to manufacture proteins.
However, when testing their theory, the team injected some of the Kit RNA proteins into mouse embryos without any forms of the mutant Kit gene, which should produce normal mice. The offspring were spotty, confirming RNA's genetic role.
'It was clear when we saw the mice born after this injection that RNA could be responsible for the inheritance of the white tail phenotype,' explained Professor Rassoulzadegan in an interview with the BBC.
The findings turn the science of genetics on its head. 'We are convinced it's a more general phenomenon,' team member Francois Cuzin at Inserm in Nice, France told Nature.
The finding goes some way to explaining recent discoveries, where heredity was passed to offspring in the absence of relevant genes. For example, studies in the late 1990s found that susceptibility to diabetes was partly determined by the region the parents were from, rather than genetic inheritance - in direct contradiction to classical Darwinian theory.
This 'behavioural imprinting' could revolutionise the way we think about genetic inheritance. The team now plan to investigate other ways in which RNA could transfer inheritable characteristics and whether such processes apply to humans. 'This brings valuable information about modification of our genome,' said Professor Rassoulzadegan, 'and perhaps this research may eventually help us to understand why we are all so different from each other.'
CORDIS RTD-NEWS/© European Communities, 2006
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