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Knocking out the genes in mice didn’t seem to do much. “I thought it must be important,” she writes.īut further experiments suggested otherwise. Over the next decade, Kaneko-Ishino’s team studied the function of RTL genes, and in experiments that would begin the new study, she compared the genomes of animals in various phylogenetic groups and found that two of these genes, RTL5 and RTL6, were evolutionarily conserved among eutherians but not in other mammals. Kaneko-Ishino's group later investigated genes with similar sequences called retrotransposon Gag-like ( RTL) genes (formerly sushi-ichi retrotransposon homolog, or SIRH, genes). See “ Viral Remnants Help Regulate Human Immunity”Įleven years later, Kaneko-Ishino and her colleagues (as well as other researchers around the same time) discovered two virus-derived imprinted genes, Peg10 and Peg11, involved in placenta formation, another mammalian innovation. She hypothesized at the time that the source of these new genes “might be exogenous DNA fragments derived from viruses, and mammals might have evolved to take advantage of them.” Genomic imprinting is unique to mammals, and Kaneko-Ishino was curious how mammals evolved imprinting-related genes. In an email to The Scientist, she writes that the new work’s roots extend back to a 1989 study on genomic imprinting, a phenomenon where maternal or paternal genes shut down the expression of genes from the other parent. Study coauthor Tomoko Kaneko-Ishino, a geneticist at Tokai University in Japan, says it took her more than 30 years to uncover the function of two virus-derived genes.
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In a study published in Development on September 26, scientists say they’ve characterized two retrovirus-derived genes that fight infections in the brains of mammals that give birth to live young, a group known as eutherians.
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Studies have found that this leftover DNA still serves crucial roles unique to mammals. At some point in evolutionary history, many of these so-called endogenous retroviruses inserted themselves into the DNA of their host, and their genetic code has been present ever since.
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Remnants of ancient viral DNA are still active in the genomes of animals alive today.
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