Synthesis and recycling of antifreeze glycoproteins in polar

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TitleSynthesis and recycling of antifreeze glycoproteins in polar fishesAbstractEvolutionary disparate Antarctic notothenioids and Arctic gadids have adapted to their freezing environments through the elaboration of essentially identical antifreeze glycoproteins (AFGPs). Here we show that this convergence of molecular identity, which evolved from unrelated parent genes, extends to convergence in physiological deployment. Both fish groups synthesize AFGPs in the exocrine pancreas from where they are discharged into the gut to inhibit the growth of ingested ice. Antifreeze glycoproteins not lost with the faeces are resorbed from the gut via the rectal epithelium, transported to the blood and ultimately secreted into the bile, from where they re-enter the gastrointestinal tract. Antifreeze glycoprotein recirculation conserves energy expenditure and explains how high levels of AFGPs reach the blood in notothenioids since, unlike Arctic gadids which also synthesize AFGP in the liver, AFGP secretion in notothenioids is directed exclusively towards the gastrointestinal lumen. Since AFGPs function by inhibiting ice crystal growth, ice must be present for them to function. The two fish groups are thus faced with an identical problem of how to deal with internal ice. Here we show that both accumulate AFGPs within ellipsoidal macrophages of the spleen, presumably adsorbed to phagocytosed ice crystals which are then held until a warming event ensues. â"' 2012 Antarctic Science Ltd.AcknowledgementsThis research was supported by the Human Frontier Science Program (grant RGP003/2009-C). We thank Antarctica New Zealand for logistic support in Antarctica, colleagues at Scott Base for assistance in the field, Dr Adrian Turner for advice with microscopy, and Vivian Ward for graphics. We are particularly grateful to Prof Jorgen Christiansen of the University of Tromso, Norway and the crew of the RV Jan Mayen for assistance in obtaining the polar cod. The constructive comments of the reviewers are also gratefully acknowledged.

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1st AuthorEvans, C.AuthorEvans, C.Hellman, L.Middleditch, M.Wojnar, J.Brimble, M.Devries, A.Year2012JournalAntarctic ScienceVolume24Number3Pages259-268DOI10.1017/S0954102012000119URLhttps://www.scopus.com/inward/recor.....277105a6a848872444dc842dbKeywordsbloodevolutionary biologyfreeze tolerancegadoidice crystalphysiological responsepolar regionpolymerizationproteinsecretion, GadidaePisces, rank5Author KeywordsAFGPArctic gadidsfreeze-avoidancenotothenioidpolar cod

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TypeArticleCitationEvans, C., Hellman, L., Middleditch, M., Wojnar, J., Brimble, M. and Devries, A. (2012). Synthesis and recycling of antifreeze glycoproteins in polar fishes. Antarctic Science, 24(3): 259-268 IdentifierEvans2012aRelevancerank5