The inheritance of white feet and white tails in mice appears to be mediated by RNA.
During most of the 20th century, the laws of inheritance discovered by Gregor Mendel 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. A new study suggests that at least one of the perpetrators of these anti-Mendelian acts is none other than RNA – a chemical ‘cousin’ of DNA.
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 grey. 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. The hypothesis is that RNA is carried in the mouse’s sperm, and at fertilisation it “silences” the activity of the normal Kit gene. This happens not only in the offspring but in subsequent generations too.
If validated, the way is open for a rethink on how RNA could influence the transmision of hereditary diseases, metabolism and even types of “imprinted” behaviour from distant generations.