politburo diktat 2.0

Researchers Discover Which Organs In Antarctic Fish Produce Antifreeze

Thirty-five years ago Arthur DeVries of the University of Illinois at Urbana-Champaign first documented antifreeze glycoproteins (AFGPs) in Antarctic notothenioid fishes. This month three colleagues report they’ve solved the ensuing, long-running mystery of where these AFGPs, which allow the fish to survive in icy waters, are produced.

“Ever since the discovery of these antifreeze proteins, it was assumed they had to be produced in the liver, since the vertebrate liver is well known as a source of secreted plasma protein, so there was no reason to think otherwise” said Chi-Hing “Christina” C. Cheng, a professor of animal biology. “It turns out that the liver has no role in the freezing avoidance in these fishes at all.”

Instead, antifreeze glycoproteins (AFGP) originate primarily from the exocrine pancreas and the stomach, say Cheng, Paul A. Cziko and Clive W. Evans in a new paper.

The exocrine pancreas is the larger of the two parts that make up the pancreas. It consists of tubuloacinar glands that primarily manufacture and secrete digestive enzymes that break down food in the intestine so it can be absorbed.

In this case, AFGPs are secreted into the intestinal lumen where they protect the intestinal fluid from being frozen by ice crystals that come in with seawater and food. Internal fluids in notothenioids are about one-half as salty as seawater. While seawater reaches its freezing point at –1.91 degrees Celsius, fish fluids freeze at about –1 degree Celsius. These species dwell in water that rarely rises above the freezing point and is regularly filled with ice crystals.