Date Published: March 13, 2012
Publisher: Public Library of Science
Author(s): Girish Neelakanta, Andrew M. Hudson, Hameeda Sultana, Lynn Cooley, Erol Fikrig, Andreas Bergmann. http://doi.org/10.1371/journal.pone.0033447
Drosophila melanogaster experience cold shock injury and die when exposed to low non-freezing temperatures. In this study, we generated transgenic D. melanogaster that express putative Ixodes scapularis antifreeze glycoprotein (IAFGP) and show that the presence of IAFGP increases the ability of flies to survive in the cold. Male and female adult iafgp-expressing D. melanogaster exhibited higher survival rates compared with controls when placed at non-freezing temperatures. Increased hatching rates were evident in embryos expressing IAFGP when exposed to the cold. The TUNEL assay showed that flight muscles from iafgp-expressing female adult flies exhibited less apoptotic damage upon exposure to non-freezing temperatures in comparison to control flies. Collectively, these data suggest that expression of iafgp increases cold tolerance in flies by preventing apoptosis. This study defines a molecular basis for the role of an antifreeze protein in cryoprotection of flies.
Arthropods have evolved various strategies – including freeze tolerance, freeze avoidance, cryoprotective dehydration and rapid cold hardening – to withstand lower environmental temperatures , . Each of these approaches is often associated with the production of specific chemicals such as antifreeze proteins , , , . Antifreeze proteins lower the freezing point of body fluids in a non-colligative manner while not significantly affecting the melting point , , , , . This property of antifreeze proteins is termed thermal hysteresis . These proteins are classified into two main types, “antifreeze proteins (AFPs)” and “antifreeze glycoproteins (AFGPs)” , , , ,  . AFPs are further divided into 4 subtypes based on the structural differences and AFGPs are divided into 8 subtypes based on the relative rates of electrophoretic migration , , , , . Since their identification in marine teleost fishes from the Antarctic , , AFPs and AFGPs have been found in various arthropods , , , , , , .
Attempts to confer cold tolerance in D. melanogaster using fish AFP type antifreeze proteins have been unsuccessful due to the decreased activity of fish AFPs when expressed in arthropods , . Arthropod AFPs are believed to have 10–30 times higher activity than fish AFPs , . The effect of arthropod AFGP type antifreeze protein on D. melanogaster cold tolerance remained unknown. We have now generated transgenic D. melanogaster that express I. scapularis AFGP and showed that this arthropod AFGP-like antifreeze protein confers cold tolerance in flies.