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Bit of a Difference in Number

A research team is casting doubts on the recent report that some 6,600 genes in the tardigrade genome were acquired through horizontal gene transfer, the Atlantic's Ed Yong reports.

Late last month, a University of North Carolina at Chapel Hill-led team reported in the Proceedings of the National Academy of Sciences that they'd generated draft tardigrade, Hypsibius dujardini, genome and sifted through it for hints as to the tardigrade's ability to withstand hard environments. Through Blast-based comparisons, the team found that about 17 percent of the tardigrade genome appeared to have foreign origins.

But, as Yong now writes, a rival team based at the University of Edinburgh and elsewhere reports in a preprint that its examination of the tardigrade genome only uncovered a handful of foreign-origin genes. The group suggested that the UNC team mistook genes from microbes that had been living with its tardigrade sample for genes from within the tardigrade genome. The Edinburgh team says that about 30 percent of the UNC-generated genome likely came such contaminants.

"If this is true, it is damning," John McCutcheon from the University of Montana tells Yong. "But it's also surprising, because much of what [the UNC team] did was pretty careful, so I would not have expected them to miss this."

In a comment on the preprint, UNC's Thomas Boothby says his team considered the possibility of contamination. "[I]t was of course the most likely initial explanation for the large amount of foreign DNA found in our assembly — and much of the analysis in our paper was designed specifically to address this issue," he says.

Boothby adds that his team is conducting additional analyses to resolve this question.

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