Gene duplication enables a novel function to evolve

The Sensuous Curmudgeon calls our attention to a new study by researchers at the University of Illnois and the Chinese Academy of Sciences that traces the evolution of a new function via gene duplication. Since I’m not a molecular guy, I’ll very briefly describe it and refer you to the news release and published paper (behind the PNAS paywall). Very briefly, the Antarctic eelpout has a gene that codes for an antifreeze protein, a member of a protein family called AFP III, that enables the eelpout to survive the freezing temperatures in Antarctic waters. It has been hypothesized on genetic homology grounds that the antifreeze gene evolved via duplication of a gene that codes for sialic acid synthase, a cellular enzyme, and subsequent selection for the antifreeze function in one of the duplicates via an escape from adaptive conflict process. From the linked news release:

“This is the first clear demonstration - with strong supporting molecular and functional evidence - of escape from adaptive conflict as the underlying process of gene duplication and the creation of a completely new function in one of the daughter copies,” Cheng said. “This has not been documented before in the field of molecular evolution.”

And from the Abstract:

We report here clear experimental evidence for EAC-driven evolution of type III antifreeze protein gene from an old sialic acid synthase (SAS) gene in an Antarctic zoarcid fish. We found that an SAS gene, having both sialic acid synthase and rudimentary ice-binding activities, became duplicated. In one duplicate, the N-terminal SAS domain was deleted and replaced with a nascent signal peptide, removing pleiotropic structural conflict between SAS and ice-binding functions and allowing rapid optimization of the C-terminal domain to become a secreted protein capable of noncolligative freezing-point depression. This study reveals how minor functionalities in an old gene can be transformed into a distinct survival protein and provides insights into how gene duplicates facing presumed identical selection and mutation pressures at birth could take divergent evolutionary paths.

As the Curmudgeon points out, this is precisely the kind of evidence that Disco ‘Tute attack mouse Casey Luskin asked for a year ago:

Many scientific papers purporting to show the evolution of “new genetic information” do little more than identify molecular similarities and differences between existing genes and then tell evolutionary just-so stories of duplication, rearrangement, and subsequent divergence based upon vague appeals to “positive selection” that purport to explain how the gene arose. But exactly how the gene arose is never explained. In particular, whether chance mutations and unguided natural selection are sufficient to produce the relevant genetic changes is almost never assessed.

There it is, Casey.