The rapid cold-hardening (RCH) response increases the cold tolerance of insects by protecting against non-freezing, cold-shock injury. Apoptosis, or programmed cell death, plays important roles in development and the elimination of sub-lethally damaged cells. Our objectives were to determine whether apoptosis plays a role in cold-shock injury and, if so, whether the RCH response protects against cold-induced apoptosis in Drosophila melanogaster. The present study confirmed that RCH increased the cold tolerance of the adults at the organismal level. No flies in the cold-shocked group survived direct exposure to 7 degrees C for 2 h, whereas significantly more flies in the RCH group survived exposure to 7 degrees C for 2 h after a 2-h exposure to 5 degrees C. We used a TUNEL assay to detect and quantify apoptotic cell death in five groups of flies including control, cold-shocked, RCH, heat-shocked (37.5 degrees C, 30 min), and frozen (20 degrees C, 24 h) and found that apoptosis was induced by cold shock, heat shock, and freezing. The RCH treatment significantly improved cell viability by 38% compared to the cold-shocked group. Cold shock-induced DNA fragmentation shown by electrophoresis provided further evidence for apoptosis. SDS-PAGE analysis revealed an RCH-specific protein band with molecular mass of approximately 150 kDa. Western-blotting revealed three proteins that play key roles in the apoptotic pathway: caspase-9-like (apoptotic initiator), caspase-3-like (apoptotic executioner) and Bcl-2 (anti-apoptotic protein). Consequently, the results of this study support the hypothesis that the RCH response protects against cold-shock-induced apoptosis.

Bile salt hydrolases were purified to electrophoretic homogeneity from Bifidobacterium bifidum ATCC 11863, Bifidobacterium infantis KL412, Bifidobacterium longum ATCC 15708, Bifidobacterium longum KL507, and Bifidobacterium longum KL515. Three different types (A, B, and C) of bile salt hydrolase (BSH) were revealed during the purification study, exhibiting the type-specific characteristics in their electrophoretic migration and elution profiles from anion exchange and hydrophobic interaction chromatographic columns. The subunit molecular mass estimated by sodium dodecylsulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) was around 35 kDa, and the native molecular mass in all five Bifidobacterium strains was estimated to be between 130 and 150 kDa by gel filtration chromatography, indicating that all BSH enzymes have tetrameric structure. From the isoelectric focusing, an isoelectric point value of 4.45 was obtained with BSH (type B) from B. bifidum ATCC 11863 and the other BSH (types A and C) showed the similar pI values around 4.65. N-Terminal amino acid sequencing for the proteins of types A and C revealed that 6 out of 20 amino acid residues were different, and highly conserved residues were identified in both N-terminal sequences of types A and C. All BSH enzymes from five strains hydrolyzed six major human bile salts, and they showed a better deconjugation rate on glycine-conjugated bile salts than on taurine-conjugated forms.

The ability to rapidly respond to changes in temperature is a critical adaptation for insects and other ectotherms living in thermally variable environments. In a process called rapid cold hardening (RCH), insects significantly enhance cold tolerance following brief (i.e., minutes to hours) exposure to nonlethal chilling. Although the ecological relevance of RCH is well-established, the underlying physiological mechanisms that trigger RCH are poorly understood. RCH can be elicited in isolated tissues ex vivo, suggesting coldsensing and downstream hardening pathways are governed by brain-independent signaling mechanisms. We previously provided preliminary evidence that calcium is involved in RCH, and here we firmly establish that calcium signaling mediates cold sensing in insect tissues. In tracheal cells of the freeze-tolerant goldenrod gall fly, Eurosta solidaginis, chilling to 0°C evoked a 40% increase in intracellular calcium concentration as determined by live-cell confocal imaging. Downstream of calcium entry, RCH conditions significantly increased the activity of calcium/calmodulin-dependent protein kinase II (CaMKII) while reducing phosphorylation of the inhibitory Thr306 residue. Pharmacological inhibitors of calcium entry, calmodulin activation, and CaMKII activity all prevented ex vivo RCH in midgut and salivary gland tissues, indicating that calcium signaling is required for RCH to occur. Similar results were obtained for a freeze-intolerant species, adults of the flesh fly, Sarcophaga bullata, suggesting that calcium-mediated cold sensing is a general feature of insects. Our results imply that insect tissues use calcium signaling to instantly detect decreases in temperature and trigger downstream cold-hardening mechanisms.ow temperature is one of the primary constraints for insects and other ectotherms living in temperate and polar regions (1). Although seasonal adaptations to cold stress, including environmentally programmed periods of dormancy called diapause, have been well-studied (2-5), physiological responses to sudden changes in temperature have received less attention. In a process termed rapid cold hardening (RCH), insects dramatically enhance their cold tolerance in a matter of minutes to hours (6). For example, in the flesh fly, Sarcophaga crassipalpis, the first species in which RCH was described, exposure to 0°C for as little as 30 min significantly enhances cold tolerance at −10°C (6). RCH has since been described in dozens of insect species (7), including both freeze-intolerant (insects in which internal ice formation is lethal) and freeze-tolerant species (insects that tolerate internal ice formation) (8, 9). Naturally occurring thermoperiods can elicit RCH (10), and RCH preserves essential functions such as courtship and mating (11,12), supporting the relevance of this process to natural populations.Although the ecological relevance of RCH has been established, the physiological mechanisms are poorly understood. RCH results in a slight increase in the cryoprotectant glycerol (6, 13),...

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.

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