Researchers have provided the first direct evidence that an evolutionarily conserved, retrotransposon-derived gene is essential for embryonic development, at least in mice, according to a study published in
This gene family originated before the emergence of placental mammals, agreed Jean-Nicolas Vollf, at the University of Würzburg in Germany, who did not participate in the study. "There is one example of the genes being present in marsupials," he said, meaning that the domestication of the retrotransposon -- which led to the formation of the
The Japanese team, led by Tomoko Kaneko-Ishino from Tokai University in Japan, studied
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Genes derived from retrotransposons could also explain the origin of epigenetic imprinting, said Volff. Cytosine methylation was originally involved in host defence against transposable elements. "That's something which is a pretty old process," he said. Since methylation is also involved in imprinting and in the inactivation of the X chromosome, this means that there are at least some common mechanisms in both processes, according to Volff. Kaneko-Ishino said his group has hypothesized that retrotransposon insertion caused the establishment of some novel imprinted regions during evolution.
The role of the gene in early placenta development is probably not the only function of the gene, however, according to Volff. "This gene is expressed in a lot of tissues and organs during embryogenesis, and in a lot of tissues and organs in adults," he said.
While he agreed that the function of
In experiments using tetraploid rescue – which involves growing embryos that have a normal placenta despite missing a developmentally important gene – the team did get some animals to go on to develop to term, he said. If a particular gene is required in other aspects of embryonic development as well as placental development, this could not happen, Surani noted.
"If [the team] looked at an earlier stage of placental development, and compared normal versus mutant [expression] in placental tissue using microarrays or something like that," Surani said, they could derive further information on the gene's function. "It would be interesting to know what the targets for this gene are," he added.