Protective agents: regulation of synthesis

Seasonal shifts in accumulation of glycerol biosynthetic gene transcripts in mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), larvae

Winter mortality is a major factor regulating population size of the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae). Glycerol is the major cryoprotectant in this freeze intolerant insect. We report findings from a gene expression study on an overwintering mountain pine beetle population over the course of 35 weeks. mRNA transcript levels suggest glycerol production in the mountain pine beetle occurs through glycogenolytic, gluconeogenic and potentially glyceroneogenic pathways, but not from metabolism of lipids. A two-week lag period between fall glycogen phosphorylase transcript and phosphoenolpyruvate carboxykinase transcript up-regulation suggests that gluconeogenesis serves as a secondary glycerol-production process, subsequent to exhaustion of the primary glycogenolytic source. These results provide a first look at the details of seasonal gene expression related to the production of glycerol in the mountain pine beetle.

Climatic variability and the evolution of insect freeze tolerance

Insects may survive subzero temperatures by two general strategies: Freeze-tolerant insects withstand the formation of internal ice, while freeze-avoiding insects die upon freezing. While it is widely recognized that these represent alternative strategies to survive low temperatures, and mechanistic understanding of the physical and molecular process of cold tolerance are becoming well elucidated, the reasons why one strategy or the other is adopted remain unclear. Freeze avoidance is clearly basal within the arthropod lineages, and it seems that freeze tolerance has evolved convergently at least six times among the insects (in the Blattaria, Orthoptera, Coleoptera, Hymenoptera, Diptera and Lepidoptera). Of the pterygote insect species whose cold-tolerance strategy has been reported in the literature, 29% (69 of 241 species studied) of those in the Northern Hemisphere, whereas 85 % (11 of 13 species) in the Southern Hemisphere exhibit freeze tolerance. A randomization test indicates that this predominance of freeze tolerance in the Southern Hemisphere is too great to be due to chance, and there is no evidence of a recent publication bias in favour of new reports of freeze-tolerant species. We conclude from this that the specific nature of cold insect habitats in the Southern Hemisphere, which are characterized by oceanic influence and climate variability must lead to strong selection in favour of freeze tolerance in this hemisphere. We envisage two main scenarios where it would prove advantageous for insects to be freeze tolerant. In the first, characteristic of cold continental habitats of the Northern Hemisphere, freeze tolerance allows insects to survive very low temperatures for long periods of time, and to avoid desiccation. These responses tend to be strongly seasonal, and insects in these habitats are only freeze tolerant for the overwintering period. By contrast, in mild and unpredictable environments, characteristic of habitats influenced by the Southern Ocean, freeze tolerance allows insects which habitually have ice nucleators in their guts to survive summer cold snaps, and to take advantage of mild winter periods without the need for extensive seasonal cold hardening. Thus, we conclude that the climates of the two hemispheres have led to the parallel evolution of freeze tolerance for very different reasons, and that this hemispheric difference is symptomatic of many wide-scale disparities in Northern and Southern ecological processes.

Recovery of human mesenchymal stem cells following dehydration and rehydration

As cell therapies advance from research laboratories to clinical application, there is the need to transport cells and tissues across long distances while maintaining cell viability and function. Currently cells are successfully stored and shipped under liquid nitrogen vapor. The ability to store these cells in the desiccated state at ambient temperature would provide tremendous economic and practical advantage. Human mesenchymal stem cells (hMSCs) have broad potential uses in tissue engineering and regeneration since they can differentiate along multiple lineages and support hematopoeisis. The current research applied recent technological advances in the dehydration and storage of human fibroblasts to hMSCs. Three conditions were tested: air-dried, air-dried and stored under vacuum (vacuum only), and incubated with 50 mM trehalose + 3% glycerol and then air-dried and stored under vacuum (vacuum + trehalose). Plates containing dehydrated hMSCs were shipped from San Diego to Baltimore overnight in separate FedEx cardboard boxes. The hMSCs were rehydrated with 3 ml of hMSC medium and were able to regain their spindle-shaped morphology and adhesive capability. In addition, they maintained high viability and proliferation capacity. Rehydrated and passaged cells continued to express the characteristic hMSC surface antigen panel. Additionally, cells showed constitutive levels of mRNA for a stromal factor and, when exposed to reagents known to induce differentiation, demonstrated upregulation of two tissue-specific messages indicative of differentiation potential for fat and bone. While our preliminary findings are encouraging, we still need to address consistency and duration of storage by considering factors such as cell water content, oxygen concentration, and the presence of free radicals.

Desiccation tolerance in human cells

The ability to desiccate mammalian cells while maintaining a high degree of viability would have implications for many areas of biological science, including tissue engineering. Previously, we reported that introduction of the genes for trehalose biosynthesis allowed human cells in culture to be reversibly desiccated for up to 5 days. Here, we have further investigated the factors that allow human cells to survive in the desiccated state. The most important finding is that vacuum greatly enhances the ability of human cells in culture to withstand desiccation. In fact, cells dried slowly and stored under vacuum are able to withstand desiccation even in the absence of added carbohydrates or polyols. In addition to vacuum, the rate of desiccation, the temperature at which cells are maintained, the degree of confluence when dried, and the presence or absence of light have a large effect on the ability to retain viability in the desiccated state. Our data are consistent with a model in which cells can retain viability if they are desiccated in such a way that cellular structures are maintained. However, gradual loss of viability may be due to damage that occurs over time in the desiccated state, perhaps due to free radicals. Further optimization of the process for desiccating and maintaining cells is required before long-term storage of desiccated cells can be achieved.

Seasonal changes in tolerance to cold and desiccation in Phauloppia sp. (Acari, Oribatida) from Finse, Norway

In the alpine region at Finse, Norway, Phauloppia spp. (Acari, Oribatida) inhabit lichens on top of boulders. Adult mites are about 0.5 mm in length and have a mean weight of ca. 15 µg. Temperatures in the lichens may drop below -35 degrees C in winter and increase to 55 degrees C in the summer. Large seasonal variations were recorded in supercooling points and body fluid osmolality. Mean January values of SCPs and osmolality were -35.3 degrees C and 3756 mOsm, while July values were -9.4 degrees C and 940 mOsm, respectively. Thermal hysteresis proteins were present in both summer and winter acclimated mites. In mid-winter, some of the mites survived more than 49 days in a water vapor saturated atmosphere at -19 degrees C, and more than 42 days enclosed in ice at the same temperature.The mites showed high tolerance to desiccation. Specimens collected in October survived up to 23 days at 22 degrees C and 5% RH. The tolerance to desiccation was lower in specimens collected during the winter. Some mites survived the loss of up to 90% of their total water content and were reactivated when given access to water. Length measurements of individual Phauloppia sp. showed that both male and female mites are clearly divided in two size groups, suggesting that they belong to two closely related species or different populations.

New phases induced by sucrose in saturated phosphatidylethanolamines: an expanded lamellar gel phase and a cubic phase

A new lamellar gel phase (L beta *) with expanded lamellar period was found at low temperatures in dihexadecylphosphatidylethanolamine (DHPE) and dipalmitoylphosphatidylethanolamine (DPPE) dispersions in concentrated sucrose solutions (1-2.4 M). It forms via a cooperative, relatively broad transition upon cooling of the L beta gel phase of these lipids. According to the X-ray data, the transformation between L beta and L beta * is reversible, with a temperature hysteresis of 6-10 degrees C and a transition width of about 10 degrees C. No specific volume changes and a very small heat absorption of about 0.05 kcal/mol accompany this transition. The L beta *-L beta transition temperature strongly depends on the disaccharide concentration. From a value of about 10 degrees C below the melting transition of DHPE, it drops by 25 degrees C with decrease of sucrose concentration from 2.4 M to 1 M. The low-temperature gel phase L beta * has a repeat spacing by 8-10 A larger than that of the L beta gel phase and a single symmetric 4.2 A wide-angle peak. It has been observed in 1, 1.25, 1.5 and 2.4 M solutions of sucrose, but not in 0.5 M of sucrose. The data clearly indicate that the expanded lamellar period of the L beta * phase results from a cooperative, reversible with the temperature, increase of the interlamellar space of the L beta gel phase. Other sugars (trehalose, maltose, fructose, glucose) induce similar expanded low-temperature gel phases in DHPE and DPPE. The L beta * phase is osmotically insensitive. Its lamellar period does not depend on the sucrose concentration, while the lattice spacings of the L alpha, L beta and HII phases decrease linearly with increase of sucrose concentration. Another notable sugar effect is the induction of a cubic phase in these lipids. It forms during the reverse HII-L alpha transition and coexists with the L alpha phase in the whole temperature range between the HII and L beta phases. The cubic phase has only been observed at sucrose concentrations of I M and above. In accordance with previous data, sucrose suppresses the L alpha phase in both lipids and brings about a direct L beta-HII phase transition in DHPE. A raid, reversible gel-subgel transformation takes place at 17 degrees C in both DPPE and DHPE. Its properties do not depend on the sucrose concentration. The observed new effects of disaccharides on the properties of lipid dispersions might be relevant to their action as natural protectants.