Study of Arctic fishes reveals the birth of a gene—from 'junk'

February 11, 2019, University of Illinois at Urbana-Champaign

Though separated by a world of ocean, and unrelated to each other, two fish groups—one in the Arctic, the other in the Antarctic—share a surprising survival strategy: They both have evolved the ability to produce the same special brand of antifreeze protein in their tissues. A new study describes in molecular detail how the Arctic fishes built the gene for their antifreeze from tiny fragments of noncoding DNA, regions once considered "junk DNA."

The findings are reported in the Proceedings of the National Academy of Sciences.

"Years ago, we discovered how antifreeze glycoproteins evolved in Antarctic notothenioid fishes, and we knew that the Arctic cod evolved an identical version—but not in the same way," said University of Illinois animal biology professor Christina Cheng, who led the new study with graduate student Xuan Zhuang. "But exactly how the codfish independently did it has remained a lasting puzzle."

To solve that puzzle, Cheng and her colleagues scoured fish and other vertebrate genomes for a gene that might have been the ancestral precursor to the codfish antifreeze gene. They came up empty, so they decided to compare the genomes of codfish that did and did not produce antifreeze protein to see how the two lineages differed. The researchers found the ancestor of the antifreeze gene in a region of noncoding DNA, which, as its name implies, does not code for a viable protein.

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