Papers by David Denlinger
American Entomologist, 1996
I N IllS INTERESTINC ARTICLE IN THE THE FALL 1994 issue (Am. Entomol. 40: 168-177), D[lvid Denlin... more I N IllS INTERESTINC ARTICLE IN THE THE FALL 1994 issue (Am. Entomol. 40: 168-177), D[lvid Denlinger describes the wonderful life of a tropic[ll beetle, StellotarslIS rotlmdlls Arrow (Endomychidae).
eLife, Jan 21, 2017
A heat exchange mechanism in the head of kissing bugs helps to prevent stress and regulate their ... more A heat exchange mechanism in the head of kissing bugs helps to prevent stress and regulate their temperature while they feed on warm blood.
Redirection of metabolism in the flesh fly
Proceedings of the National Academy of Sciences of the United States of America, Jan 10, 2011
The mosquito's body temperature increases dramatically when it takes a blood meal from a warm... more The mosquito's body temperature increases dramatically when it takes a blood meal from a warm-blooded, vertebrate host. By using the yellow fever mosquito, Aedes aegypti, we demonstrate that this boost in temperature following a blood meal prompts the synthesis of heat shock protein 70 (Hsp70). This response, elicited by the temperature of the blood meal, is most robust in the mosquito's midgut. When RNA interference is used to suppress expression of hsp70, protein digestion of the blood meal is impaired, leading to production of fewer eggs. We propose that Hsp70 protects the mosquito midgut from the temperature stress incurred by drinking a hot blood meal. Similar increases in hsp70 were documented immediately after blood feeding in two other mosquitoes (Culex pipiens and Anopheles gambiae) and the bed bug, Cimex lectularius, suggesting that this is a common protective response in blood-feeding arthropods.
PLoS Genetics, 2014
In tsetse flies, nutrients for intrauterine larval development are synthesized by the modified ac... more In tsetse flies, nutrients for intrauterine larval development are synthesized by the modified accessory gland (milk gland) and provided in mother's milk during lactation. Interference with at least two milk proteins has been shown to extend larval development and reduce fecundity. The goal of this study was to perform a comprehensive characterization of tsetse milk proteins using lactation-specific transcriptome/milk proteome analyses and to define functional role(s) for the milk proteins during lactation. Differential analysis of RNA-seq data from lactating and dry (non-lactating) females revealed enrichment of transcripts coding for protein synthesis machinery, lipid metabolism and secretory proteins during lactation. Among the genes induced during lactation were those encoding the previously identified milk proteins (milk gland proteins 1-3, transferrin and acid sphingomyelinase 1) and seven new genes (mgp4-10). The genes encoding mgp2-10 are organized on a 40 kb syntenic block in the tsetse genome, have similar exon-intron arrangements, and share regions of amino acid sequence similarity. Expression of mgp2-10 is female-specific and high during milk secretion. While knockdown of a single mgp failed to reduce fecundity, simultaneous knockdown of multiple variants reduced milk protein levels and lowered fecundity. The genomic localization, gene structure similarities, and functional redundancy of MGP2-10 suggest that they constitute a novel highly divergent protein family. Our data indicates that MGP2-10 function both as the primary amino acid resource for the developing larva and in the maintenance of milk homeostasis, similar to the function of the mammalian casein family of milk proteins. This study underscores the dynamic nature of the lactation cycle and identifies a novel family of lactation-specific proteins, unique to Glossina sp., that are essential to larval development. The specificity of MGP2-10 to tsetse and their critical role during lactation suggests that these proteins may be an excellent target for tsetsespecific population control approaches.
Tissue and Cell, 1993
The ultrastructure of the ring gland (corpus cardiacurn (CC). prothoraw gland (PG) and corpus all... more The ultrastructure of the ring gland (corpus cardiacurn (CC). prothoraw gland (PG) and corpus allatum (CA)) was examined in diapausing and nondiapausing flesh fly pupae. The diapause developmental state, which is environmentally regulated and coordinated by the brain-ring gland complex, is associated with differences in the ultrastructure of PG and CA cells but not in the CC. During diapause the PG and CA cells have extensive arr,ays of rough cndoplasmic reticulum and spherical mitochondria. The PG cells also contain hpld droplets surrounded by an electron dense amorphous coat not seen m PG cells from nondiapausmg pupae. In nondiapausing pupae. the PG and CA cells contain large amounts of rihosomcs throughout the cytoplasm but very little rough endoplasmic reticulum and elongated mitochondria. The fact that ring glands from diapausing pupae readily incorporate "S-methionmc indicates that the gland is actively synthesizing proteins. thus the contrasts in rmg gland ultrastructure are not due to cellular quiescence during diapause but reflect fundamental cellular and physiological differences between the diapause and nondiapause developmental program
Journal of Experimental Biology, 2009
SUMMARY Summer storms along the Antarctic Peninsula can cause microhabitats of the terrestrial mi... more SUMMARY Summer storms along the Antarctic Peninsula can cause microhabitats of the terrestrial midge Belgica antarctica to become periodically inundated with seawater from tidal spray. As microhabitats dry, larvae may be exposed to increasing concentrations of seawater. Alternatively, as a result of melting snow or following rain, larvae may be immersed in freshwater for extended periods. The present study assessed the tolerance and physiological response of B. antarctica larvae to salinity exposure, and examined the effect of seawater acclimation on their subsequent tolerance of freezing, dehydration and heat shock. Midge larvae tolerated extended exposure to hyperosmotic seawater; nearly 50% of larvae survived a 10-day exposure to 1000 mOsm kg–1 seawater and ∼25% of larvae survived 6 days in 2000 mOsm kg–1 seawater. Exposure to seawater drastically reduced larval body water content and increased hemolymph osmolality. By contrast,immersion in freshwater did not affect water content...
Science, 2014
Africa's Bane Tsetse are blood-feeding, fast-flying flies that transmit a range of Trypanosom... more Africa's Bane Tsetse are blood-feeding, fast-flying flies that transmit a range of Trypanosoma spp. protozoan pathogens, which cause sleeping sickness in humans and their nagana in their livestock. The International Glossina Genome Initiative (p. 380 ) sequenced the genome of Glossina morsitans and identified the genes for many attributes of the tsetse's remarkable biology, including viviparity and the expression of analogs of mammalian milk proteins. Tsetse are host to several specific symbionts that appear to synthesize essential nutrients for the fly and also to hitherto undiscovered parasitoid-derived viruses. Deeper exploration of this genome will reveal what makes these fly species so host- and trypanosome specific.
PROTEOMICS, 2009
Desiccation presents a major challenge for the Antarctic midge, Belgica antarctica. In this study... more Desiccation presents a major challenge for the Antarctic midge, Belgica antarctica. In this study, we use proteomic profiling to evaluate protein changes in the larvae elicited by dehydration and rehydration. Larvae were desiccated at 75% relative humidity (RH) for 12 h to achieve a body water loss of 35%, approximately half of the water that can be lost before the larvae succumb to dehydration. To evaluate the rehydration response, larvae were first desiccated, then rehydrated for 6 h at 100% RH and then in water for 6 h. Controls were held continuously at 100% RH. Protein analysis was performed using 2-DE and nanoscale capillary LC/MS/MS. Twenty-four identified proteins changed in abundance in response to desiccation: 16 were more abundant and 8 were less abundant; 84% of these proteins were contractile or cytoskeletal proteins. Thirteen rehydration-regulated proteins were identified: 8 were more abundant and 5 were less abundant, and 69% of these proteins were also contractile or cytoskeletal proteins. Additional proteins responsive to desiccation and rehydration were involved in functions including stress responses, energy metabolism, protein synthesis, glucogenesis and membrane transport. We conclude that the major protein responses elicited by both desiccation and rehydration are linked to body contraction and cytoskeleton rearrangements.
Polar Biology, 2007
Three species of Antarctic mites, Alaskozetes antarcticus, Hydrogamasellus antarcticus and Rhagid... more Three species of Antarctic mites, Alaskozetes antarcticus, Hydrogamasellus antarcticus and Rhagidia gerlachei, are abundant in the vicinity of Palmer Station, Antarctica. No single mechanism for reducing water stress was shared by all three species. A. antarcticus and R. gerlachei (both ca. 200 lg) are over twice as large as H. antarcticus (ca. 90 lg), but all had similar body water content (67%) and tolerated a loss of up to 35% of their body water before succumbing to dehydration. All imbibed free water and had the capacity to reduce water loss behaviorally by forming clusters. Alaskozetes antarcticus was distinct in that it relied heavily on water conservation (xerophilic classification) that was largely achieved by its thick cuticular armor, a feature shared by all members of this suborder (Oribatida), and abundant cuticular hydrocarbons. In comparison to the other two species, A. antarcticus was coated with 2-39 the amount of cuticular hydrocarbons, had a 20-fold reduction in net transpiration rate, and had a critical transition temperature (CTT) that indicates a pronounced suppression in activation energy (E a) at temperatures below 25°C. In contrast, H. antarcticus and R. gerlachei lack a CTT, have lower amounts of cuticular hydrocarbons and have low E a s and high net transpiration rates, classifying them as hydrophilic. Only H. antarcticus was capable of utilizing water vapor to replenish its water stores, but it could do so only at relative humidities close to saturation (95-98 %RH). Thus, H. antarcticus and R. gerlachei require wet habitats and low temperature to counter water loss, and replace lost water behaviorally through predation. Compared to mites from the temperate zone, all three Antarctic species had a lower water content, a feature that commonly enhances cold tolerance.
Polar Biology, 2008
In January 2007 we discovered numerous large aggregations of collembolan eggs on Humble Island ne... more In January 2007 we discovered numerous large aggregations of collembolan eggs on Humble Island near Palmer Station (64°46ЈS, 64°03ЈW). These aggregations were found in damp areas under rocks, moss, mats of the terrestrial alga Prasiola crispa, and at the interface between vegetation and the rocky substrate. Aggregations ranged in size from hundreds of eggs to the largest, whose estimated size exceeded 2 million eggs. Such aggregations were not observed in previous years. Associated with these aggregations were two collembolan species, Cryptopygus antarcticus (Willem) and Friesea grisea (SchaVer). Spring warming occurred approximately 7 weeks earlier in 2006 compared to the previous year. This early warming and consequent extended period of relatively high temperatures may have modiWed thermal and hydric conditions favoring collembolan growth and development and the formation of these large aggregations.
Microbiology, 2007
Members of the Mycobacterium tuberculosis complex show distinct host preferences, yet the molecul... more Members of the Mycobacterium tuberculosis complex show distinct host preferences, yet the molecular basis for this tropism is unknown. Comparison of the M. tuberculosis and Mycobacterium bovis genome sequences revealed no unique genes in the bovine pathogen per se, indicating that differences in gene expression may play a significant role in host predilection. To define the key gene expression differences between M. tuberculosis and M. bovis we have performed transcriptome analyses of cultures grown under steady-state conditions in a chemostat. This revealed that the human and bovine pathogens show differential expression of genes encoding a range of functions, including cell wall and secreted proteins, transcriptional regulators, PE/PPE proteins, lipid metabolism and toxin-antitoxin pairs. Furthermore, we probed the gene expression response of M. tuberculosis and M. bovis to an acid-shock perturbation which triggered a notably different expression response in the two strains. Through these approaches we have defined a core gene set that shows differential expression between the human and bovine tubercle bacilli, and the biological implications are discussed.
Medical and Veterinary Entomology, 2009
This study of the bed bug, Cimex lectularius, examines tolerance of adult females to extremes in ... more This study of the bed bug, Cimex lectularius, examines tolerance of adult females to extremes in temperature and loss of body water. Although the supercooling point (SCP) of the bed bugs was approximately −20 • C, all were killed by a direct 1 h exposure to −16 • C. Thus, this species cannot tolerate freezing and is killed at temperatures well above its SCP. Neither cold acclimation at 4 • C for 2 weeks nor dehydration (15% loss of water content) enhanced cold tolerance. However, bed bugs have the capacity for rapid cold hardening, i.e. a 1-h exposure to 0 • C improved their subsequent tolerance of−14 and −16 • C. In response to heat stress, fewer than 20% of the bugs survived a 1-h exposure to 46 • C, and nearly all were killed at 48 • C. Dehydration, heat acclimation at 30 • C for 2 weeks and rapid heat hardening at 37 • C for 1 h all failed to improve heat tolerance. Expression of the mRNAs encoding two heat shock proteins (Hsps), Hsp70 and Hsp90, was elevated in response to heat stress, cold stress and during dehydration and rehydration. The response of Hsp90 was more pronounced than that of Hsp70 during dehydration and rehydration. Our results define the tolerance limits for bed bugs to these commonly encountered stresses of temperature and low humidity and indicate a role for Hsps in responding to these stresses.
Journal of Insect Physiology, 2007
The Antarctic midge, Belgica antarctica, is exposed to frequent periods of dehydration during its... more The Antarctic midge, Belgica antarctica, is exposed to frequent periods of dehydration during its prolonged larval development in the cold and dry Antarctic environment. In this study, we determined the water requirements of the larvae and the mechanisms it exploits to reduce the stress of drying. Larvae lost water at an exceptionally high rate (410%/h) and tolerated losing a high portion (470%) of their water content. Larvae were unable to absorb water from subsaturated water vapor (p0.98 a v) to replenish their water stores, thus this midge relies exclusively on the intake of liquid water to increase its pool of body water and maintain water balance. To reduce dehydration stress, the midge employed a variety of mechanisms. Behaviorally, the larvae suppressed water loss by clustering. In response to slow dehydration, glycerol concentration increased 2-fold and trehalose concentration increased 3-fold, responses that are known to decrease the rate of water loss and increase dehydration tolerance. No changes in the mass of cuticular lipids occurred in response to desiccation, but the observed shift to longer hydrocarbons likely contributes to reduced water loss as the larvae dehydrate. As the larvae dehydrated, their oxygen consumption rate dropped, resulting in a reduction of water loss by respiration. Lastly, one bout of slow dehydration also enhanced the larva's ability to survive subsequent dehydration, suggesting that the larvae have the capacity for drought acclimation. Thus, these hydrophilic midge larvae prevent dehydration by multiple mechanisms that collectively reduce the water loss rate and increase dehydration tolerance.
Journal of Insect Physiology, 2007
Insects in diapause characteristically feed very little or not at all, thus they are largely or t... more Insects in diapause characteristically feed very little or not at all, thus they are largely or totally dependent on energy reserves sequestered prior to the entry into diapause. Fats are the dominant reserve used during this period, but non-fat reserves are also important for some species, especially during certain phases of diapause. Metabolic depression, coupled with the low temperatures of winter, facilitates the economic utilization of reserves during the many months typical of most diapauses. Though many insects store additional lipid prior to the entry into diapause, our review of the literature indicates that this is not always the case. We provide evidence that interactions between nutrient storage and metabolism can influence the decision to enter diapause and determine how long to remain in diapause. In addition, the energy reserves expended during diapause have a profound effect on post-diapause fitness. Though the physiological and biochemical mechanisms that regulate nutrient homeostasis prior to and during diapause remain poorly known, we propose several mechanisms that have the potential to contribute to diapause-associated nutrient homeostasis. Potential players include insulin signaling, neuropeptide F, cGMP-kinase, AMP-activated protein kinase, and adipokinetic hormone.
Journal of Insect Physiology, 2008
The abundance and activity of many soil-dwelling organisms depends upon the moisture characterist... more The abundance and activity of many soil-dwelling organisms depends upon the moisture characteristics of their environment. This is especially true in the Antarctic where water availability, even more so than temperature, is recognized as the most important determinant of the distribution of Antarctic terrestrial organisms (Kennedy, 1993). During winter, habitat moisture is likely to be limited, as water is biologically unavailable in the form of ice. Similarly, during summer terrestrial microhabitats may dry depending on the vagaries of precipitation, wind, temperature and insolation in relation to soil and vegetation type (Kennedy, 1993). Therefore, desiccation resistance and/or tolerance of varying relative humidity (RH) conditions are likely to be as important as cold tolerance for the survival of terrestrial organisms in polar environments (Ring and Danks, 1994; Block, 1996). Collembolans are among the most abundant and widespread terrestrial arthropods and have been classified into three groups based upon their response to desiccating conditions (Vannier, 1983).
Journal of Insect Physiology, 2010
This study examines the responses of heat shock protein transcripts, Hsp70 and Hsp90, to dehydrat... more This study examines the responses of heat shock protein transcripts, Hsp70 and Hsp90, to dehydration stress in three mosquito species, Aedes aegypti, Anopheles gambiae and Culex pipiens. We first defined the water balance attributes of adult females of each species, monitored expression of the hsp transcripts in response to dehydration, and then knocked down expression of the transcripts using RNA interference (RNAi) to evaluate potential functions of the Hsps in maintenance of water balance. Fully hydrated females of all three species contained nearly the same amount of water (66-68%), but water loss rates differed among the species, with A. aegypti having the lowest water loss rate (2.6%/h), followed by C.pipiens (3.3%/h), and A. gambiae (5.1%/h). In all three species water could be replaced only by drinking water (or blood). Both A. aegypti and C. pipiens tolerated a loss of 36% of their body water, but A. gambiae was more vulnerable to water loss, tolerating a loss of only 29% of its body water. Dehydration elicited expression of hsp70 in all three species, but only C. pipiens continued to express this transcript during rehydration. Hsp90 was constitutively expressed and expression levels remained fairly constant during dehydration and rehydration, except expression was not noted during rehydration of C. pipiens. Injection of dsRNA to knock down expression of hsp70 (83% reduction) and hsp90 (46% reduction) in A. aegypti did not alter water content or water loss rates, but the dehydration tolerance was lower. Instead of surviving a 36% water loss, females were able to survive only a 28% water loss in response to RNAi directed against hsp70 and a 26% water loss when RNAi was directed against hsp90. These results indicate a critical function for these Hsps in mosquito dehydration tolerance
Journal of Insect Physiology, 2008
The midge, Belgica antarctica Jacobs, is subjected to numerous environmental stressors during its... more The midge, Belgica antarctica Jacobs, is subjected to numerous environmental stressors during its 2-year life cycle on the Antarctic Peninsula, and in response it has evolved a suite of behavioral, physiological, and life-cycle modifications to counter these stressors, but thus far only a limited number of biochemical adaptations have been identified. In this study, we use a metabolomics approach to obtain a broad overview of changes in energy metabolism, amino acids, and polyols in response to three of the midge's major stresses: heat, freezing, and desiccation. Using GC-MS analysis, a total of 75 compounds were identified. Desiccation (50% water loss) elicited the greatest physiological response (as determined by principal components analysis) when compared to untreated controls, with many elevated metabolites from pathways of central carbohydrate metabolism and a decrease in free amino acids. When larvae were frozen (6 h at À10 1C), alanine and aspartate increased as well as urea. Freezing also increased three polyols (glycerol, mannitol, erythritol), while desiccation increased only two polyols (glycerol, erythritol). Heating the midges for 1 h at 30 1C elevated a-ketoglutarate and putrescine while suppressing glycerol, glucose, and serine levels. Freezing and desiccation elicited elevation of four shared metabolites, whereas no shared metabolites were elevated by heat. All three treatments resulted in a reduction in serine, potentially identifying this amino acid as a marker for stress in this species. A number of metabolic changes, especially those in the sugar and polyol pools, are adaptations that have potential to enhance survival during both cold and desiccation.
Journal of Comparative Physiology B, 2009
We investigated molecular responses elicited by three types of dehydration (fast, slow and cryopr... more We investigated molecular responses elicited by three types of dehydration (fast, slow and cryoprotective), rehydration and overhydration in larvae of the Antarctic midge, Belgica antarctica. The larvae spend most the year encased in ice but during the austral summer are vulnerable to summer storms, osmotic stress from ocean spray and drying conditions due to wind and intense sunlight. Using suppressive subtractive hybridization (SSH), we obtained clones that were potentially responsive to dehydration and then used northern blots to evaluate the gene's responsiveness to diVerent dehydration rates and hydration states. Among the genes most responsive to changes in the hydration state were those encoding heat shock proteins (smHsp, Hsp70, Hsp90), antioxidants (superoxide dismutase, catalase), detoxiWcation (metallothionein, cytochrome p450), genes involved in altering cell membranes (fatty acid desaturase, phospholipase A2 activating protein, fatty acyl CoA desaturase) and the cytoskeleton (actin, muscle-speciWc actin), and several additional genes including a zinc-Wnger protein, pacifastin and VATPase. Among the three types of dehydration evaluated, fast dehydration elicited the strongest response (more genes, higher expression), followed by cryoprotective dehydration and slow dehydration. During rehydration most, but not all, genes that were expressed during dehydration continued to be expressed; fatty acid desaturase was the only gene to be uniquely upregulated in response to rehydration. All genes examined, except VATPase, were upregulated in response to overhydration. The midge larvae are thus responding quickly to water loss and gain by expressing genes that encode proteins contributing to maintenance of proper protein function, protection and overall cell homeostasis during times of osmotic Xux, a challenge that is particularly acute in this Antarctic environment.
Journal of Comparative Physiology B, 2006
The seabird tick Ixodes uriae is exposed to extreme environmental conditions during the off-host ... more The seabird tick Ixodes uriae is exposed to extreme environmental conditions during the off-host phase of its life cycle on the Antarctic Peninsula. To investigate how this tick resists desiccation, water requirements of each developmental stage were determined. Features of I. uriae water balance include a high percentage body water content, low dehydration tolerance limit, and a high water loss rate, which are characteristics that classify this tick as hydrophilic. Like other ticks, I. uriae relies on water vapor uptake as an unfed larva and enhanced water retention in the adult, while nymphs are intermediate and exploit both strategies. Stages that do not absorb water vapor, eggs, fed larvae and fed nymphs, rely on water conservation. Other noteworthy features include heat sensitivity that promotes water loss in eggs and unfed larvae, an inability to drink free water from droplets, and behavioral regulation of water loss by formation of clusters. We conclude that I. uriae is adapted for life in a moisture-rich environment, and this requirement is met by clustering in moist, hydrating, microhabitats under rocks and debris that contain moisture levels that are higher than the tick's critical equilibrium activity. Keywords Water balance Á Dehydration Á Tick Á Ixodes Á Antarctica Communicated by I.D. Hume.
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Papers by David Denlinger