Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers discover which organs in Antarctic fish produce antifreeze

20.06.2006
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 paper appearing online this week ahead of regular publication in the Proceedings of the National Academy of Sciences.

Cziko is a research specialist at Illinois. Evans is a professor of molecular genetics and development at the University of Auckland in New Zealand.

The liver-synthesis mindset dominated earlier studies even though results appeared to be at odds, Cheng said. The first radioactive-tracer characterization of liver AFGP biosynthesis, in fact, suggested another source of production was possible. Later on, Northern-blot studies had shown very low expression levels of antifreeze messenger RNA in the liver, but this was inconsistent with high levels of production of the protein, the researchers noted.

Cheng and colleagues used Northern blots of total RNA from various tissues to hybridize with an AFGP gene probe. A clear picture of strong AFGP mRNA expression came into focus in the pancreatic tissues in all notothenioids tested. The use of cDNA cloning and sequencing showed that the mRNA all encode secreted AFGPs.

An RNA analysis from tissues of a single notothenioid unveiled the anterior portion of the stomach, next to the esophagus-stomach junction, as being the only other site with strong AFGP mRNA expression. Using antibodies, the researchers found the absence of liver synthesis and strong pancreas expression in newly hatched fish larvae and young juveniles.

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.

From the intestine, the AFGPs are, apparently, absorbed into the blood. This hypothesis is based on the near-identical composition and abundance of AFGPs found in the fish serum.

"In this comprehensive study, we confirm that the exocrine pancreas is the major AFGP synthesis site in Antarctic notothenioid fishes from hatching through adulthood, while the liver is AFGP-expression null in all life stages," the researchers conclude. "Because the notothenioids are confined to chronically icy Antarctic waters, and face high risks of ice inoculation from frequent seawater drinking, the evolution of AFGPs in these fishes was probably driven first and foremost by the need to prevent the hyposmotic intestinal fluid from freezing."

The researchers also studied a variety of fishes from Arctic waters that have liver expression of AFGPs, and found that all of them also express antifreeze in the pancreas.

The findings, they wrote, bring a new perspective to teleost freeze-avoidance physiology and "reveals that the long-held paradigm of hepatic-based AF synthesis and secretion is no longer universally applicable." Instead, pancreatic antifreeze expression is universal.

Jim Barlow | EurekAlert!
Further information:
http://www.uiuc.edu

More articles from Life Sciences:

nachricht Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery
20.01.2017 | GSI Helmholtzzentrum für Schwerionenforschung GmbH

nachricht Seeking structure with metagenome sequences
20.01.2017 | DOE/Joint Genome Institute

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>