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In tale of the tail, RNA's role detailed

Study shows mice got trait, not gene

NEW YORK -- In a startling exception to classical genetics, mice in a lab experiment have inherited an effect of an aberrant gene without inheriting the gene itself.

Specialists say the result could someday help scientists understand aspects of diabetes, infertility, and other problems. But they also said that while such an inheritance pattern has been seen before, it's not clear how common or important it is.

DNA holds genetic material in mice and humans. But the new study indicates DNA's chemical cousin, RNA, produced the odd-sounding result. In this case, the result was mice with distinctive white tail tips.

For the study, reported in yesterday's issue of the journal Nature, scientists produced mice that carried one normal copy of a particular gene and one aberrant copy. When the scientists bred them, each mouse passed along one of its gene copies to each offspring. The offspring, in turn, ended up with two copies, one from each parent.

Under the rules of classical genetics, one would expect that mice ending up with two normal copies of the gene would show normal coloring. But surprisingly, 24 out of 27 mice with two normal copies still showed the telltale white patches associated with the aberrant copy of the gene.

Experiments showed the trait could be inherited through either the mother or father, and it went on for generations in absence of the abnormal gene.

To determine why this occurred, researchers focused on sperm, which is simpler to analyze than an egg. They found evidence that RNA molecules were carrying the hereditary signal. For example, when RNA from mice bearing the aberrant gene was injected into early embryos, about half the resulting mice showed the distinctive white tail tip.

RNA normally delivers instructions from genes to a cell's protein-making machinery, so it makes sense that it might be involved in transmitting a gene's effect. Just how it's operating in the mice is not clear, said lead study author Minoo Rassoulzadegan of the University of Nice in France.

Paul Soloway of Cornell University, who was not involved in the study, said that when viewed in context with other research, the new RNA evidence is ``compelling."

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