Aquaporins play a role in desiccation and freeze tolerance in larvae of the goldenrod gall fly, Eurosta solidaginis

Abstract

SUMMARYSurvival of freezing not only requires organisms to tolerate ice formation within their body, but also depends on the rapid redistribution of water and cryoprotective compounds between intra-and extracellular compartments. Aquaporins are transmembrane proteins that serve as the major pathway through which water and small uncharged solutes (e.g. glycerol) enter and leave the cell. Consequently, we examined freeze-tolerant larvae of the goldenrod gall fly, Eurosta solidaginis, to determine whether aquaporins are present and if their presence promotes freeze tolerance of specific tissues. Immunoblotting with mammalian anti-AQP2, -AQP3 and -AQP4 revealed corresponding aquaporin homologues in E. solidaginis, whose patterns of expression varied depending on acclimation temperature and desiccation treatment. To examine the role of aquaporins in freeze tolerance, we froze fat body, midgut and salivary gland tissues in the presence and absence of mercuric chloride, an aquaporin inhibitor. Survival of fat body and midgut cells was significantly reduced when mercuric chloride was present. In contrast, survival of the salivary gland did not decrease when it was frozen with mercuric chloride. Overall, this study supports our hypothesis that naturally occurring aquaporins in E. solidaginis are regulated during desiccation and promote cell survival during freezing.

The protective role of aquaporins in the freeze-tolerant insect Eurosta solidaginis: functional characterization and tissue abundance of EsAQP1

“…The permeability of AQP/GLPs to these molecules implicates these proteins in protecting against freeze-induced damage in a range of organisms, including yeast (Tanghe et al, 2002), insects (Izumi et al, 2006;Philip et al, 2008) and amphibians (Zimmerman et al, 2007). The ability of EsAQP1 channels to redistribute water across the membrane faster than by simple diffusion through membrane, as shown by our in vitro assay (Fig.4), would facilitate cellular dehydration that is caused by the formation of concentrated extracellular fluid during freezing.…”

“…AQPs, which rapidly redistribute water and certain small solutes across the membrane, are associated with the physiological response to stresses that require the management of cellular water, such as anhydrobiosis (Kikawada et al, 2008), feeding on osmotically challenging foods (Le Caherec et al, 1996;Shakesby et al, 2009) and survival of freezing (Izumi et al, 2006;Philip et al, 2008;Philip and Lee, 2010). To better understand the role of these proteins in osmotic stress, we identified, functionally characterized the water permeability and determined the tissue distribution of an AQP during seasonal cold acclimation in E. solidaginis.…”

“…Our experimental evidence demonstrated that EsAQP1 is impermeable to glycerol (Fig.5), and therefore we suggest another AQP isoform is responsible for the movement of this cryoprotectant during larval freezing. Based on previous studies, which identified multiple AQP-and GLP-like proteins in E. solidaginis (Philip et al, 2008;Philip and Lee, 2010), and the putative number of AQPs existing in insect genomes [seven in Drosophila spp. and five in mosquito (Campbell et al, 2008)], EsAQP1 is likely only one of several AQP/GLP isoforms involved in glycerol and/or water redistribution during osmotic challenge.…”

“…Our previous study demonstrated that tissues from E. solidaginis are unable to survive freezing in the presence of an AQP/GLP inhibitor (Philip et al, 2008). This result suggests a critical role for AQPs/GLPs in facilitating water exosmosis and/or cryoprotectant (e.g.…”

“…Aquaglyceroporins (GLPs), a subgroup of AQPs permeable to water and small uncharged solutes (Borgnia et al, 1999), are implicated in the cellular movement of glycerol during freezing (Izumi et al, 2006;Philip and Lee, 2010;Philip et al, 2008;Zimmerman et al, 2007). The importance of glycerol uptake through GLPs in freezing survival is suggested by the improved cryopreservation survival of mouse oocytes that artificially express GLPs (Edashige et al, 2003).…”