Nature 's roundup of the papers and issues gaining traction on social media.

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Just how much of our genome serves a purpose anyway? A recent study reignited the debate on this, particularly on social media. Researchers also took to Twitter to discuss a newly discovered yet remarkably abundant virus, and to snicker over its unique name.

After comparing the genomes of 12 different mammals (including humans, mice and pandas), researchers at the University of Oxford, UK, concluded that only about 8.2% of the human genome is shaped by natural selection. The rest, they argue, is non-functional. Observers noted the large difference between this estimate and a previous claim by the ENCODE (Encyclopedia of DNA Elements) Project that 80% of the genome is biochemically active. Patrik D'haeseleer, a computational biologist at Lawrence Livermore National Laboratory, California, tweeted “only between 8% and 80% of human #genome is functional. Glad we've got that sorted out.” At the heart of the issue are differing definitions of 'function'. Erick Loomis, an epigeneticist at Imperial College London, tweeted: “Maybe we should stop using 'functional' if we can't find a common definition.”

The attempts to define genome function have been mired in controversy since ENCODE published its '80%' finding in 2012 (Nature 489, 57–74; 2012). A subsequent paper from the same consortium a few months ago also met with derision, partly because it didn't even speculate on the fraction of the genome that might have a purpose (M. Kellis et al. Proc. Natl Acad. Sci. USA 111, 6131–6138; 2014). That paper did, however, argue that evolutionary, genetic and biochemical data need to be taken into account to work out the answer.

In the latest report, the Oxford researchers responded to that call by focusing on evolutionary data. They looked for parts of the genome that showed low rates of mutation, a sign that those regions were conserved through natural selection. They classified the sequences — and only those sequences — as functional, a definition that is at odds with that used by ENCODE, which equated biochemical activity with functionality.

The shifting definitions confused some readers. “I don't get this paper,” tweeted John Greally, an epigeneticist at the Albert Einstein College of Medicine of Yeshiva University in New York City. “Functional=conserved, but discussion acknowledges that function can be in non-conserved sequences?” When reached for further comment, Greally says that he “gets” the paper now, but that he is “still frustrated by the way this debate is causing so much unproductive friction”.

The paper, Greally says, missed an opportunity to explore why certain sequences — especially those known as transcription factor binding sites — are under such low evolutionary pressure, even though they presumably have important biological roles. Instead, he adds, the authors emphasized the supposed discrepancy with ENCODE. “The paper appears to be in use as a bludgeon with which to hammer the ENCODE project, not necessarily by the authors, but by others,” he suggests.

One outspoken critic of ENCODE is Dan Graur, who studies molecular evolutionary bioinformatics at the University of Houston, Texas. He publicly celebrated the new paper by tweeting: “What an amazing birthday present.” In a follow-up interview, he said that the paper refutes ENCODE's claims, and added that it is “idiotic” to suggest that a part of the genome could be functional if it didn't respond to pressure from natural selection.

ENCODE member Ross Hardison, a molecular biologist at Pennsylvania State University, called the latest paper “elegant” even though it took a different view of functionality. The Oxford group's findings don't contradict those of ENCODE, he says, because the project never estimated the proportion of the genome that would be conserved through natural selection. He added that it will probably take a combination of approaches to determine which parts of the genome we can't live without. “I expect that with more experiments and analyses, estimates of the proportion of the human genome that is functional will approach some convergence, even though they are pretty far apart now.”

Rands, C. M., Meader, S., Ponting, C. P. & Lunter, G. PLoS Genet. 10, e1004525 (2014)

Others on Twitter were tickled by the name of an abundant virus that infects bacteria, which has made its way into the guts of more than half of humans without anyone noticing — until now. An international group of researchers discovered evidence of the virus, a bacteriophage named crAssphage, by studying published data on microbial DNA collected from human faeces. Some people on social media managed to restrict their comments to the scientific implications of the work. “Phage find is also a great example of how new computational methods enable new biology,” tweeted Robin Friedman, a computational biologist at the Institut Pasteur in Paris.

Others found humour in the name crAssphage. “Nomenclature at its finest,” tweeted Jason Petitjean, a medical student at Louisiana State University Health Sciences Center in Shreveport. But microbiologist Steven Hecht, of Grand Valley State University in Allendale, Michigan, took the high ground on Twitter, noting that the name comes from the software program used in the paper. “The name of the phage is derived from the cross-assembly used to piece it together, not the site” where it was found, but he agreed in a later tweet that the name was clever PR.

The virus seems to be enjoying its newfound fame — it has its own hashtag (#crAssphage) and has decided to move beyond the human gut and make Twitter its home too. “Hello world! I've been hiding for centuries in your guts, but now I'm finally discovered!” said @crassphage.

Dutilh, B. E. et al. Nature Commun. 5, 4498 (2014)