BIO 205 Detailed Outline
Detailed Focus Question: How are antifreeze glycoproteins utilized by Antarctic Notothenioid fishes to avoid freezing in polar oceans? Where are they synthesized and distributed and how do they allow the Antarctic Nototheniids to survive in polar oceans?
Introduction: Marine invertebrates and fishes exhibit a variety of environmental adaptations to survive in freezing polar oceans. One of the best examples of these adaptations is the use of antifreeze glycoproteins in Antarctic Nototheniids. The introduction will be used to give a brief overview of antifreeze glycoproteins (AFGPs) and the Antarctic nototheniids while the rest of the paper will examine selected areas more thoroughly.
Where Antarctic Nototheniids are found
Antarctic fishes are able to survive in the freezing waters of the Southern Ocean which is an extremely inhospitable environment for marine life (Evans, Hellman, Middleditch, et al. 2012)
This environment makes the possibility of ice internalizing very high. (Evans, Hellman, Middleditch, et al. 2012)
Temperature effects of AFGPs on Antarctic Nototheniids
Antarctic Nototheniids inhabit areas of the Antarctic ocean with water as cold as –1.9 degrees Celsius. (Ahlgren, Cheng, Schrag, DeVries, 1988)
AFGPs lower the freezing point of Antarctic Nototheniids to between –2.2 and –2.7 degrees Celsius. (Ahlgren, Cheng, Schrag, DeVries, 1988)
How antifreeze glycoproteins work
AFGPs bind irreversibly to ice
AFGPs utilize an adsorption-inhibition mechanism through irreversible binding of the AFGPs to ice crystals which prevents further growth of the ice. (Meister, DeVries, Bakker, Drori, 2018)
Microfluidics and fluorescent microscopy have been used to show that small and large AFGP isoforms bind irreversibly to ice crystals. (Meister, DeVries, Bakker, Drori, 2018)
AFGP adsorption rate decreased by 65% in the presence of borate, which is an inhibitor of AFGP activity. (Meister, DeVries, Bakker, Drori, 2018)
For AFGPs to inhibit ice growth, high adsorption rate is necessary. (Meister, DeVries, Bakker, Drori, 2018)
Internal ice crystals may be removed from circulation by phagocytosis.
AFGP coated fluorescent nanoparticles were found in splenic phagocytes 4-6 hours after intravenous injection. (Evans, Gubala, Nooney, et al. 2010)
When AFGP binds to ice crystals, it may then be removed from circulation by splenic phagocytes. (Evans, Gubala, Nooney, et al. 2010)
Intracellular sequestration of ice in the spleen may reduce the risk of circulating ice and allow the ice to be stored until a later date when it can be disposed of by a seasonal warming event or melting. (Evans, Gubala, Nooney, et al. 2010)
Where Antifreeze Glycoproteins are produced, recycled, and distributed
Synthesis of AFGPs
AFGPs are synthesized in the pancreas as well as in the liver (Evans, Hellman, Middleditch, et al. 2012)
The synthesizing of AFGPs in both the pancreas and the liver allows for AFGPs to directly enter the blood stream via the liver and protect the digestive tract against ingested ice by the AFGPs produced in the pancreas. (Evans, Hellman, Middleditch, et al. 2012)
Recycling of AGPs
Some AFGPs released by the pancreas can be reabsorbed by epithelial cells and enter into the blood (Evans, Hellman, Middleditch, et al. 2012)
AFGPs that reach the liver are transferred into bile, pass through the gallbladder, and then released back into the digestive tract. (Evans, Hellman, Middleditch, et al. 2012)
Nonhepatic Origin of AFGPs
Northern Blot analysis indicates that the pancreas and anterior stomach are sites of AFGP synthesis in addition to the liver (Cheng, Cziko, Evans, 2006)
Distribution of AFGPs in body fluids
Peritoneal, pericardial, and extradural fluids contained significant amounts of AFGPs to reduce freezing point in Antarctic Nototheniids. (Ahlgren, Cheng, Schrag, DeVries, 1988)
Urine, endolymph, aqueous humour and vitreous humour fluids showed low levels of AFGPs in Antarctic Nototheniids that would prevent those fluids from having a freezing point below that of the water in their environment. (Ahlgren, Cheng, Schrag, DeVries, 1988)
External mucus of Antarctic nototheniids contains AFGPs which may serve as a protective role against the entry of ice. (Evans, Gubala, Nooney, et al. 2010)
Distribution of AFGPs in Tissues
All tissues examined showed AFGPs in interstitial fluid except for brain tissue.(Ahlgren, Cheng, Schrag, DeVries, 1988)
No AFGPs were observed to be taken up intracellularly from the blood. (Ahlgren, Cheng, Schrag, DeVries, 1988)
Conclusion: This paragraph will briefly summarize the function and importance of antifreeze glycoproteins in Antarctic Nototheniids. It will emphasize the novel function of AFGPs compared to other marine animals. The paragraph will also discuss areas in which further research could be conducted and the significance of the research.