Biology subjects

Andersen, M. K.

Publications and source records attributed to Andersen, M. K..

At least 19 recordsLinked to original sources

bioRxiv2026

A conserved cold stress syndrome defines insect chill tolerance

The ability to withstand cold is arguably one of the most important traits defining the biogeographical distribution of insects. For most species, those classified as chill susceptible, cold tolerance is limited by the ability to maintain vital physiological functions at low temperature. However, there is currently no unified understanding of how physiological failure develops during cold stress or how this process explains variation in cold sensitivity within and among species. Although disruption of ion homeostasis has been implicated in chilling injury, it remains unclear whether it represents a common physiological limit across cold stress intensities and degrees of chill tolerance. Here, we tested whether ion balance disruption represents a unifying physiological syndrome of chill susceptibility by simultaneously quantifying cold mortality and hemolymph [K] in Drosophila. We examined this relationship across i) a broad range of cold stress intensities, ii) 25 species spanning extensive variation in cold sensitivity, biogeography and phylogeny, and iii) acclimation groups of D. melanogaster developed between 12 and 27{degrees}C. Across all comparisons, mortality was associated with the same cold-stress response, characterized by progressive hyperkalemia and mortality following a ~150% increase in hemolymph [K] above baseline ([K]crit). In contrast, adaptive and plastic variation in cold sensitivity was explained by differences in the critical temperature at which ion homeostasis failed (Tc). Extending this framework to published data from other insect orders revealed a remarkably similar [K]crit, suggesting that ionoregulatory collapse represents a conserved physiological constraint defining insect cold survival.

physiology↗

bioRxiv2026

Integrated multi-omics profiling uncovers the epigenetic, transcriptional, and metabolic landscape of prostate cancer progression

A comprehensive understanding of the underlying molecular mechanisms of prostate cancer is essential for the development of precise diagnostic biomarkers. In this study, we applied unsupervised multi-omics factor analysis (MOFA) to integrate DNA methylation, gene expression, and metabolic profiles derived from the same individuals, aiming to characterize the biological landscape of normal, malignant, and aggressive prostate tissue. Our analysis identified distinct molecular pathways associated with aggressive disease, specifically those involved in zinc metabolism, cell cycle regulation, smooth muscle architecture, immune activation, and tissue morphology. Key metabolites within the TCA cycle, amino acid metabolism, and lipid pathways were central to these signatures. Furthermore, we observed a consistent co-enrichment of SP1 and CTCFL binding regions among factor-associated CpGs, suggesting a model of global epigenetic reprogramming. These findings indicate a novel interplay between Polycomb deregulation, CTCFL-mediated chromatin remodeling, and SP1-driven transcriptional activation in shaping the prostate cancer epigenome. Apart from immune activation, the identified molecular signatures were validated in the TCGA cohort and demonstrated significant predictive value for disease recurrence. Overall, these results underscore the power of multi-omics integration in providing a holistic understanding of prostate cancer biology and its potential for clinical translation into prognostic biomarkers.

cancer biology↗

bioRxiv2026

Using thermal death time models to analyze cold stress resistance across Drosophila species

O_LIChill-susceptible insects such as Drosophila are vulnerable to progressive disruption of ion and water homeostasis during cold stress, and low temperature exposure is a key factor affecting their physiology and distribution. Comparative studies of cold tolerance traditionally use simple or single-condition assays for interspecific comparisons, but the emergence of thermal death time (TDT) models offers a comprehensive framework to assess cold tolerance across different stress intensities and durations. C_LIO_LIHere we construct TDT curves for six Drosophila species, spanning boreal to tropical habitats, using Lt50 estimates across a range of stressful low temperatures (Lt50 ranging from [~] 20 min to 2 days). For all species, the TDT curves provided good fits to the log(Lt50) vs. temperature data (R2 = 0.87 - 0.99). C_LIO_LITDT curves from all species had steep slopes demonstrating that cold injury rate has a high thermal sensitivity such that small changes in temperature have profound effects on survival duration. The interspecific similarity of TDT slopes indicates that a conserved physiological dysfunction underlies cold injury across species. Further, additive accumulation of cold-induced injury in split-dose experiments suggests that acute and moderate cold damage represent the same underlying physiological dysfunction occurring at different rates. C_LIO_LIThe TDT curve intercepts (species-specific tolerance thresholds) differed markedly between boreal, temperate, and tropical species and correlated strongly with their habitat temperature. Data from the present study and meta-analysis of published data find that the inherent species cold tolerance decreases by [~] 0.45 {degrees}C for each {degrees}C colder the winter environment of the species is. When also considering the cold acclimation cues in cold climates we argue the experienced level of cold stress intensity is similar across environments inhabited by the Drosophila genus. This suggests that cold tolerance is important in shaping the fundamental niche of both boreal and tropical species. C_LIO_LIOverall, the TDT analysis of Drosophila at low temperature provides a powerful and predictive tool for quantifying insect cold tolerance. This approach enables detailed cross-species comparisons that allows for both ecological and physiological inference. Thus, TDT curves offer relevant approximations of insect cold resistance that could help predict insect responses to climatic change. C_LI

ecology↗

bioRxiv2025

Chill tolerant Drosophila species maintain electrogenic muscle membrane potential to resist cold-induced depolarization

The ability to tolerate low temperature is among the most important traits defining the functional niche of insects and it clear that cold tolerance of most insects is intimately linked to their ability to defend membrane potential (Vm). Failure to maintain membrane polarization results in loss of neuromuscular function and may ultimately initiate cell death and organismal injury. Prolonged cold exposure challenges membrane polarization through loss of transmembrane ion balance; however, the insect muscle Vm is also dependent on a strong and temperature-dependent electrogenic effect driven by Na+/K+-ATPase activity. In the present study we investigate the electrogenic contribution of the Na+/K+-ATPase at benign (20{degrees}C) and low (0{degrees}C) temperature in ten Drosophila species representing a broad spectrum of chill tolerance. We find that the electrogenic effect of the Na+/K+-ATPase contributes a considerable component of the muscle Vm in all ten species at 20{degrees}C. This electrogenic contribution is reduced significantly at 0{degrees}C in the chill sensitive species, while tolerant species retain their electrogenic effect at low temperature. Thus, the initial cold-induced muscle depolarization, that is a hallmark of chill sensitive insects, is largely caused by loss of Na+/K+-ATPase-dependent electrogenic polarization. We hypothesized that maintenance of Na+/K+-ATPase activity in the cold would be energetically costly, but in contrast to our hypothesis we find no evidence for major energetic costs in the species that maintain membrane polarization at low temperature. On the basis of these observations we discuss how other adaptations at the protein or membrane level could explain the observed intraspecific differences.

physiology↗

bioRxiv2024

Glial voltage-gated K+ channels modulate the neural abiotic stress tolerance of Drosophila melanogaster

Severe abiotic stress causes insects to lose nervous function and enter a state of paralytic coma. Central to this loss of function is a spreading depolarization (SD), where a characteristic collapse of ion gradients depolarizes neuronal and glial membranes and rapidly shuts down the CNS. Despite representing a critical limit to CNS function, the stress threshold that elicits SD can be altered by the process of acclimation, though the mechanisms underlying this response remain largely unknown. Here, we made electrophysiological measurements of SD and investigated the role of K+ channels in acclimation of the CNS stress response of Drosophila melanogaster. First, we demonstrate that improved cold tolerance in the CNS elicited by cold acclimation was abolished by pharmacological blockade of K+ channels with voltage-gated K+ channels representing most of this effect. Next, we used the UAS/Gal4 model system to screen for candidate genes encoding glial voltage-gated K+ channels and found that knockdown of sei- and Shaw-encoded channels mimicked the effect of K+ blockade in cold-acclimated flies. Furthermore we show that the knockdown of glial sei-encoded channels also impair tolerance to anoxia and heat stress. These findings suggest that voltage-gated K+ channels, especially those encoded by sei, are integral to the CNS stress- and acclimation-response and we posit that this is elicited through mechanisms involving glial spatial buffering and barrier function. Establishing such causal links between tissue-specific expression of candidate genes and SD mechanisms will inevitably aid our understanding of insect ecophysiology and SD-related neuropathologies. New and NoteworthyUsing thermal acclimation and pharmacology, we demonstrate that voltage-gated K+ channels are involved in setting the threshold for cold-induced spreading depolarization (SD) in the Drosophila melanogaster CNS. Glial knockdown of channels encoded by sei and Shaw reduced the resistance to cold-induced SD, highlighting their importance in acclimation of the CNS. Glia-specific sei-knockdown also reduced tolerance to anoxia and heat. We posit that sei-channels are involved the CNS stress- and acclimation-responses through glial spatial buffering mechanisms.

neuroscience↗

bioRxiv2024

Spatial Integration of Multi-Omics Data using the novel Multi-Omics Imaging Integration Toolset

To truly understand the cancer biology of heterogenous tumors in the context of precision medicine, it is crucial to use analytical methodology capable of capturing the complexities of multiple omics levels, as well as the spatial heterogeneity of cancer tissue. Different molecular imaging techniques, such as mass spectrometry imaging (MSI) and spatial transcriptomics (ST) achieve this goal by spatially detecting metabolites and mRNA, respectively. To take full analytical advantage of such multi-omics data, the individual measurements need to be integrated into one dataset. We present MIIT (Multi-Omics Imaging Integration Toolset), a Python framework for integrating spatially resolved multi-omics data. MIITs integration workflow consists of performing a grid projection of spatial omics data, registration of stained serial sections, and mapping of MSI-pixels to the spot resolution of Visium 10x ST data. For the registration of serial sections, we designed GreedyFHist, a registration algorithm based on the Greedy registration tool. We validated GreedyFHist on a dataset of 245 pairs of serial sections and reported an improved registration performance compared to a similar registration algorithm. As a proof of concept, we used MIIT to integrate ST and MSI data on cancer-free tissue from 7 prostate cancer patients and assessed the spot-wise correlation of a gene signature activity for citrate-spermine secretion derived from ST with citrate, spermine, and zinc levels obtained by MSI. We confirmed a significant correlation between gene signature activity and all three metabolites. To conclude, we developed a highly accurate, customizable, computational framework for integrating spatial omics technologies and for registration of serial tissue sections.

bioinformatics↗

bioRxiv2024

Thermal acclimation of spreading depolarization in the CNS of Drosophila melanogaster

During exposure to extreme stress, the CNS of mammals and insects fails through a phenomenon known as spreading depolarization (SD). SD is characterized by an abrupt disruption of ion gradients across neural and glial membranes that spreads through the CNS, silencing neural activity. In humans, SD is associated with neuropathological conditions like migraine and stroke. In insects, it is coincident with critical thermal limits for activity and can be conveniently monitored by observing the transperineurial potential (TPP). We used the TPP to explore the temperature-dependence and plasticity of SD thresholds and SD-induced changes to the TPP in fruit flies (Drosophila melanogaster) acclimated to different temperatures. Specifically, we characterized the effects of thermal acclimation on the TPP characteristics of cold-induced SD, after which we induced SD via anoxia at different temperatures in both acclimation groups to examine the interactive effects of temperature and acclimation status. Lastly, we investigated these effects on the rate of SD propagation across the fruit fly CNS. Cold acclimation enhanced resistance to both cold- and anoxic SD and our TPP measurements revealed independent and interactive effects of temperature and acclimation on the TPP and SD propagation. This suggests thermodynamic processes and physiological mechanisms interact to modulate the threshold for activity through SD and its electrophysiological phenomenology. These findings are discussed in relation to conceptual models for SD and established mechanisms for variation in the thermal threshold for SD.

physiology↗

bioRxiv2024

Dietary potassium and cold acclimation additively increase cold tolerance in Drosophila melanogaster

In the cold, chill susceptible insects lose the ability to regulate ionic and osmotic gradients. This leads to hemolymph hyperkalemia that drives a debilitating loss of cell membrane polarization, triggering cell death pathways and causing organismal injury. Biotic and abiotic factors can modulate insect cold tolerance by impacting the ability to mitigate or prevent this cascade of events. In the present study, we test the combined and isolated effects of dietary manipulations and thermal acclimation on cold tolerance in fruit flies. Specifically, we acclimated adult Drosophila melanogaster to 15 or 25{degrees}C and fed them either a K+-loaded diet or a control diet. We then tested the ability of these flies to recover from and survive a cold exposure, as well as their capacity to protect transmembrane K+ gradients, and intracellular Na+ concentration. As predicted, cold-exposed flies experienced hemolymph hyperkalemia and cold-acclimated flies had improved cold tolerance due to an improved maintenance of the hemolymph K+ concentration at low temperature. Feeding on a high-K+ diet improved cold tolerance additively, but paradoxically reduced the ability to maintain extracellular K+ concentrations. Cold-acclimation and K+-feeding additively increased the intracellular K+ concentration, aiding in maintenance of the transmembrane K+ gradient during cold exposure despite cold-induced hemolymph hyperkalemia. There was no effect of acclimation of diet on intracellular Na+ concentration. These findings suggest intracellular K+ loading and reduced muscle membrane K+ sensitivity as mechanisms through which cold-acclimated and K+-fed flies are able to tolerate hemolymph hyperkalemia. Highlights- Insect cold tolerance varies in relation to ionoregulatory capacity - Cold acclimation improves cold tolerance and K+ handling during cold exposure - A high K+ diet also improves cold tolerance, but reduces the K+-handling capacity - We highlight a novel mechanism for preventing K+ gradient disruption

physiology↗

bioRxiv2024

Deep phenotyping of the prostate tumor microenvironment reveals molecular stratifiers of relapse and links inflammatory chemokine expression to aberrant metabolism

Understanding the molecular characteristics and changes of the tumor microenvironment (TME) associated with aggressive prostate cancer (PCa) is essential for precise diagnosis and treatment. We interrogated spatially resolved integrated transcriptomics and metabolomics data to build molecular strafiers discriminating patients with aggressive, potentially relapsing, and metastasizing PCa. We report a relapse associated (RA) gene expression signature characterized by upregulated immune response related gene expression scoring high in cancer, stroma, and glandular tissue of relapsing patients. Further, we identified a signature specific to a distinct sub-group of morphologically non-cancerous glands in prostate tissue from patients with relapsing cancer. This signature, named chemokine-enriched-gland (CEG) signature, was characterized by upregulated gene expression of pro-inflammatory chemokines. Glands with a high CEG score were enriched for club-like cells and surrounding stroma was infiltrated by immune cells. Tissue regions scoring high for both CEG and RA signatures were associated with reduced levels of citrate and zinc and loss of normal prostate secretory gland functions via reduced expression of genes necessary for citrate secretion. In summary we report that aggressive PCa is associated with an increased inflammatory status linked to chemokine production and club-like cell enrichment in potentially pre-cancerous prostate glands displaying an aberrant metabolism.

cancer biology↗

bioRxiv2024

Sucrase isomaltase dysfunction influences dietary sucrose intake and preference

ObjectiveTo characterise the role of Sucrase-isomaltase (SI) in regulating dietary behaviours, such as sweet preference and food liking in Si knockout (Sis-KO) mice and in population-based cohorts from Greenland and the UK. DesignWe profiled the appetitive and post-ingestive response to dietary carbohydrates in SI knockout (Sis-KO) mice. Alongside this, we conducted detailed dietary analysis of 45 foods in two Greenlandic population-based cohorts (IHIT, n=2778 and 68 foods, and B2018, n=2203 and 45 foods) with the presence of a common (allele frequency = 14.3%) SI Loss of function (LoF) variant, c.273-274delAG. Finally, we explored the association between SI hypomorphic variants, liking of 140 foods, and sucrose content using data from 134,766 UKBB participants with exome sequencing and questionnaire data available. ResultsSucrose naive Sis-KO mice had a significantly reduced intake of dietary sucrose, and preference for 10% liquid sucrose, in two-bottle preference studies. Mechanistically, oral administration of the short-chain fatty acid acetate reduced sucrose-preference in wild-type mice. In Greenlandic LoF homozygous carriers we show that the previously reported reduction in sugar intake may primarily be explained by a lower intake of cake and pastries, and of candy and chocolate and that added sugar is the main factor explaining these associations. In the UKBB, a negative association with "cake icing", the food with the highest sucrose content per 100g, was detected in SI hypomorphic carriers, as well as in sensitivity analyses conducted only including carriers of known CSID LoF variants. Further, a negative linear relationship was also observed between the effect estimates of hypomorphic SI variants on food liking and the estimated sucrose content per 100g of 88 sucrose-containing foods, indicating that food dislike in SI carriers correlates with the amount of sucrose in food. ConclusionCollectively, we demonstrated that genetic variation in the SI gene is associated with significant changes in sucrose preference, characterised by a rapid avoidance of dietary sucrose in Sis-KO mice, as well as lower consumption and increased disliking of sucrose rich foods in Greenlanders and Europeans, respectively. This work demonstrates that genetic variation in the SI gene may impact physiology beyond the gastrointestinal tract and suggest the possibility to target SI to reduce the preference, and intake, of dietary sucrose with implications for digestive and metabolic health.

genetics↗

bioRxiv2024

Androgen deprivation therapy-resistant club cells are linked to myeloid cell-driven immunosuppression in the prostate tumor microenvironment

Prostate cancer treatment resistance is a significant challenge facing the field. Genomic and transcriptomic profiling have partially elucidated the mechanisms through which cancer cells escape treatment, but their relation toward the tumor microenvironment (TME) remains elusive. Here we present a comprehensive transcriptomic landscape of the prostate TME at multiple points in the standard treatment timeline employing single-cell RNA-sequencing and spatial transcriptomics data from 110 patients. We identify club-like cells as a key epithelial cell subtype that acts as an interface between the prostate and the immune system. Tissue areas enriched with club-like cells have depleted androgen signaling and upregulated expression of luminal progenitor cell markers. Club-like cells display a senescence-associated secretory phenotype and their presence is linked to increased polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC) activity. Our results indicate that club-like cells partake in inducing myeloid inflammation previously associated with androgen deprivation therapy resistance, providing a rationale for their therapeutic targeting.

cancer biology↗

bioRxiv2024

The freeze-avoiding mountain pine beetle (Dendroctonus ponderosae) survives prolonged exposure to stressful cold by mitigating ionoregulatory collapse

Insect performance is intrinsically linked to environmental temperature, and surviving through winter represents a key challenge for temperate, alpine, and polar species. To overwinter, insects have adapted a wide range of strategies to become truly cold hardy. However, while the physiological mechanisms underlying the ability to avoid or tolerate freezing have been well-studied, little attention has been given to the challenge of maintaining ion homeostasis at frigid temperatures in these species, despite this being a central issue for insects susceptible to mild chilling. Here we investigate how prolonged exposure to temperatures just above the supercooling point affects ion balance in freeze-avoiding larvae of the mountain pine beetle (Dendroctonus ponderosae) in autumn, mid-winter, and spring, and relate it to organismal recovery times and survival outcomes. We found that hemolymph ion balance was gradually disrupted during the first day of exposure, characterized by hyperkalemia and hyponatremia, after which a plateau was reached and maintained for the rest of the seven day experiment. The degree of ionoregulatory collapse experienced by larvae correlated strongly with recovery times, which followed a similar asymptotical progression. Mortality increased slightly during the most severe cold exposures, where hemolymph K+ concentration was highest, and a logistic relationship was found between survival and hyperkalemia. Thus, the cold tolerance of the freeze-avoiding larvae of D. ponderosae appears limited by the ability to prevent ionoregulatory collapse in a manner similar to less tolerant chill-susceptible insects, albeit at much lower temperatures. Furthermore, we posit that a prerequisite for the evolution of insect freeze avoidance is a convergent or ancestral ability to maintain ion homeostasis during exposure to extreme cold stress.

physiology↗

bioRxiv2023

Tropical butterflies lose central nervous system function in the cold from a spreading depolarization event

Insects are ectotherms and their physiological functions are therefore directly influenced by the environmental temperature. By extension, their ability to tolerate thermal extremes is directly linked to their thermal niche and distribution. Understanding the physiological mechanisms that limit insect thermal tolerance is therefore crucial for our ability to predict biogeography and range shifts. Recent studies on fruit flies and locusts suggest that the loss of coordinated movements at the critical thermal minimum is due to a loss of central nervous system function via a spreading depolarization. We hypothesized that a similar mechanism limits nervous function in other insect taxa. Here, we use electrophysiology to investigate whether the same spreading depolarization event occurs in the brain of butterflies exposed to stressful cold. Supporting our hypothesis, we find that exposure to stressful cold induced spreading depolarization in all species tested. This reinforces the idea that loss of central nervous function by a spreading depolarization is a common mechanism underlying the critical thermal minimum in insects. Furthermore, our results highlight how central nervous system performance is finely tuned to match species environments. Further research into the physiological mechanisms underlying the spreading depolarization event is likely to elucidate key mechanisms determining insect ecology.

physiology↗

bioRxiv2022

Plasticity in Na+/K+-ATPase thermal kinetics drives variation in the critical thermal minimum of adult Drosophila melanogaster

The majority of insects can acclimate to changes in their thermal environment and counteract temperature effects on neuromuscular function. At the critical thermal minimum a spreading depolarization (SD) event silences central neurons, but the temperature at which this event occurs can be altered through acclimation. SD is triggered by an inability to maintain ion homeostasis in the extracellular space in the brain and is characterized by a rapid surge in extracellular K+ concentration, implicating ion pump and channel function. Here, we focused on the role of the Na+/K+-ATPase specifically in lowering the SD temperature in cold-acclimated D. melanogaster. After first confirming cold acclimation altered SD onset, we investigated the dependency of the SD event on Na+/K+-ATPase activity by injecting an inhibitor, ouabain, into the head of the flies to induce SD over a range of temperatures. Latency to SD followed the pattern of a thermal performance curve, but cold acclimation resulted in a left-shift of the curve to an extent similar to its effect on the SD temperature. With Na+/K+-ATPase activity assays and immunoblots, we found that cold-acclimated flies have ion pumps that are less sensitive to temperature, but do not differ in their overall abundance in the brain. Combined, these findings suggest a key role for plasticity in Na+/K+-ATPase thermal sensitivity in maintaining central nervous system function in the cold, and more broadly highlight that a single ion pump can be an important determinant of whether insects can respond to their environment to remain active at low temperatures.

physiology↗

bioRxiv2022

Elemental stoichiometry and insect chill tolerance: Evolved and plastic changes in organismal Na+ and K+ content in Drosophila

Acclimation and evolutionary adaptation can produce phenotypic change that allows organisms to cope with challenges like those associated with climate change. Determining the relative contributions of acclimation and adaptation is of central importance to understanding animal responses to change. Rates of evolution have traditionally been considered slow relative to ecological processes that shape biodiversity. Many organisms nonetheless show patterns of spatial genetic variation suggestive of adaptation and some evidence is emerging that adaptation can act sufficiently fast to allow phenotypic tracking in response to environmental change ( adaptive tracking). In Drosophila, both plastic and evolved differences in chill tolerance are associated with ionoregulation. Here we combine acclimation, latitudinal field collections, and a replicated field experiment to assess the effects of acclimation and adaptation on chill coma recovery and elemental (Na and K) stoichiometry in both sexes of Drosophila melanogaster. Acclimation and spatial adaptation both shape chill coma recovery, with acclimation producing the greatest magnitude response. Leveraging knowledge on the physiological mechanisms that underlie variation in chill tolerance traits, we find that the relationship between K content and chill tolerance differs among flies acclimated vs. adapted to cold. Taken together, these data reinforce the importance of acclimation in responses to abiotic challenges and illustrate that the mechanisms of phenotypic change can differ between acclimation and basal tolerance adaptation.

evolutionary biology↗

bioRxiv2020

Thermal acclimation alters the roles of Na+/K+-ATPase activity in a tissue-specific manner in Drosophila melanogaster

Insects, like the model species Drosophila melanogaster, lose neuromuscular function and enter a state of paralysis (chill coma) at a population- and species-specific low temperature threshold that is decreased by cold acclimation. Entry into this coma is related to a spreading depolarization in the central nervous system, while recovery involves restoration of electrochemical gradients across muscle cell membranes. The Na+/K+-ATPase helps maintain ion balance and membrane potential in both the brain and hemolymph (surrounding muscles), and changes in thermal tolerance traits have therefore been hypothesized to be closely linked to variation in the expression and/or activity of this pump in multiple tissues. Here, we tested this hypothesis by measuring activity and thermal sensitivity of the Na+/K+-ATPase at the tagma-specific level (head, thorax and abdomen) in warm-(25{degrees}C) and cold-acclimated (15{degrees}C) flies by Na+/K+-ATPase activity at 15, 20, and 25{degrees}C. We relate differences in pump activity to differences in chill coma temperature, spreading depolarization temperature, and thermal dependence of muscle cell polarization. Differences in pump activity and thermal sensitivity induced by cold acclimation varied in a tissue-specific manner: While cold-acclimated flies had decreased thermal sensitivity of Na+/K+-ATPase that maintains activity at low temperatures in the thorax (mainly muscle), activity instead decreased in the heads (mainly brain). We argue that these changes may assist in maintenance of K+ homeostasis and membrane potential across muscle membranes and discuss how reduced Na+/K+-ATPase activity in the brain may counterintuitively help insects delay coma onset in the cold.

physiology↗

bioRxiv2020

Hyperkalemia, not apoptosis, accurately predicts insect chilling injury

During prolonged or severe chilling, the majority of insects accrue chilling injuries that are typically quantified by scoring neuromuscular function after rewarming. In the cold, these chill susceptible insects, like the migratory locust (Locusta migratoria) suffer a loss of ion and water balance that is hypothesized to initiate cell death. Whether apoptotic or necrotic cell death pathways are responsible for this chilling injury is unclear. Here, we use a caspase-3 specific assay to indirectly quantify apoptosis in three locust tissues (muscle, nerves, and midgut) following prolonged chilling and recovery from an injury-inducing cold exposure. Furthermore, we obtain matching measurements of injury, hemolymph [K+], and muscle caspase-3 activity in individual locusts to gain further insight into mechanistic nature of chilling injury. We hypothesized that apoptotic cell death in both muscle and nerve tissue drives motor defects following cold exposure in insects, and that there would be a strong association between cold- induced injury, hyperkalemia, and muscle caspase-3 activity. We found a significant increase in muscle caspase-3 activity, but no such increase was observed in either nervous or gut tissue from the same animals, suggesting that chill injury primarily relates to apoptotic muscle cell death. However, the levels of chilling injury measured at the whole animal level prior to tissue sampling were strongly correlated with the degree of hemolymph hyperkalemia, but not apoptosis. These results support the notion that cold-induced ion balance disruption triggers cell death but also that apoptosis is not the main cell death pathway driving injury in the cold. Significance StatementTemperature has profound effects on animal fitness and sets limits to animal distribution. To understand and model insect responses to climate, we need to know how temperature sets limits to their survival. There is strong evidence that a collapse of ion and water balance occurs in insects in the cold, and it is generally held that the resulting cold injury is caused by activation of programmed cell death (apoptosis). Here, we directly test this idea and show for the first time that although the loss of ion balance is a strong predictor of individual survival outcomes, apoptosis is not the primary cause of cold-induced injury.

physiology↗

bioRxiv2019

Inter- and intraspecific differences in Drosophila cold tolerance are linked to hindgut reabsorption capacity

Maintaining extracellular osmotic and ionic homeostasis is crucial to maintain organismal function. In insects, hemolymph volume and ion content is regulated by the combined actions of the secretory Malpighian tubules and reabsorptive hindgut. When exposed to stressful cold, homeostasis is gradually disrupted, characterized by a debilitating increase in extracellular K+ concentration (hyperkalemia). In accordance with this paradigm, studies have found a strong link between the cold tolerance of insect species and their ability to maintain ion and water homeostasis at low temperature. This is also the case for drosophilids where studies have already established how inter- and intra-specific differences in cold tolerance are linked to the secretory capacity of Malpighian tubules. However, presently there is little information on the effects of temperature on the reabsorptive capacity of the hindgut in Drosophila. To address this question we developed a novel method that allows for continued measurements of hindgut ion and fluid reabsorption in Drosophila. Firstly we demonstrate that this assay is temporally stable (> 3 hours) and that the preparation is responsive to humoral stimulation and pharmacological intervention of active and passive transport in accordance with the current insect hindgut reabsorption model. Using this method at benign (24{degrees}C) and low temperature (3{degrees}C) we investigated how cold acclimation or cold adaptation affected the thermal sensitivity of osmoregulatory function. We found that cold tolerant Drosophila species and cold-acclimated D. melanogaster are innately better at maintaining rates of fluid and Na+ reabsorption at low temperature. Furthermore, cold adaptation and acclimation causes a relative reduction in K+ reabsorption at low temperature. These characteristic responses of cold adapted/acclimated Drosophila will act to promote maintenance of ion and water homeostasis at low temperature and therefore provide further links between adaptations in osmoregulatory capacity of insects and their ability to tolerate cold exposure.

physiology↗