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ABSTRACT: Terrestrial arthropods that reside in Antarctica are exposed to considerable periods of environmental stress, thus factors
that promote identification of favorable microhabitats are extremely important. In this study, we report the presence of chemical
cues that induce oviposition and aggregation in two species of Antarctic collembolans, Cryptopygus antarcticus and Friesea grisea. Responses of the Collembola were enhanced by low temperatures but were not altered by humidity. One of the major physiological
benefits derived from an aggregation was a substantial reduction in water loss rates. Although F. grisea and C. antarcticus were commonly found in cross-species aggregations, we found no evidence to suggest cross-species attraction. When individuals
were exposed to areas previously occupied by groups of Collembola, more eggs were laid. Thus, chemicals released by the collembolans
appear to induce both aggregation and oviposition in these Antarctic species.
Journal of Insect Behavior 04/2012; 22(2):121-133. · 0.96 Impact Factor
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ABSTRACT: 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. 200μg) are over twice as large as H. antarcticus (ca. 90μg), 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 2–3× 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
as 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 04/2012; 31(5):539-547. · 1.66 Impact Factor
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ABSTRACT: We cloned the gene that encodes prothoracicotropic hormone (PTTH) in the northern house mosquito, Culex pipiens, and investigated its expression profile in short-day (diapause-destined) and long-day (nondiapause-destined) individuals from the fourth-instar larval stage to 2 months of adulthood, as well as after a blood meal. The deduced C. pipiens PTTH (Cupip-PTTH) amino acid sequence contains seven cysteines with a specific spacing pattern. Sequence alignment suggests that Cupip-PTTH is 23% identical to Drosophila melanogaster PTTH, but is ≥59% identical to the PTTHs of other mosquitoes. Cupip-PTTH has structural characteristics similar to those of Bombyx mori PTTH and some vertebrate nerve growth factors with cysteine-knot motifs. PTTH transcripts exhibit a daily cycling profile during the final (fourth) larval instar, with peak abundance occurring late in the scotophase. The fourth-larval instar stage is one day longer in short-day larvae than in long-day larvae, resulting in larger larvae and adults. This additional day of larval development is associated with one extra PTTH cycle. No cycling was observed in pupae, but PTTH transcripts were slightly higher in short-day pupae than in long-day pupae throughout much of the pupal stage. PTTH expression persisted at a nearly constant level in diapausing adult females for the first month but then dropped by ∼50%, while expression decreased at the beginning of adulthood in nondiapausing females and then remained at a low level as long as the females were denied a blood meal. However, when nondiapausing females were offered a blood meal, PTTH transcripts rose approximately 7 fold in 2 h and remained elevated for 24 h. A few diapausing females (∼10%) will take a blood meal when placed in close proximity to a host, but much of the blood is ejected and such meals do not result in mature eggs. Yet, elevated PTTH mRNA expression was also observed in diapausing females that were force fed. Our results thus point to several distinctions in PTTH expression between short-day and long-day mosquitoes, but both types of females responded to a blood meal by elevating levels of PTTH mRNA.
Insect Molecular Biology 11/2010; 20(2):201-13. · 2.53 Impact Factor
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ABSTRACT: 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 degrees C, all were killed by a direct 1 h exposure to -16 degrees C. Thus, this species cannot tolerate freezing and is killed at temperatures well above its SCP. Neither cold acclimation at 4 degrees 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 degrees C improved their subsequent tolerance of -14 and -16 degrees C. In response to heat stress, fewer than 20% of the bugs survived a 1-h exposure to 46 degrees C, and nearly all were killed at 48 degrees C. Dehydration, heat acclimation at 30 degrees C for 2 weeks and rapid heat hardening at 37 degrees 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.
Medical and Veterinary Entomology 12/2009; 23(4):418-25. · 1.91 Impact Factor
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ABSTRACT: Arrested ovarian development is a key characteristic of adult diapause in the mosquito Culex pipiens. In this study we propose that ribosomal protein S3a (rpS3a), a small ribosomal subunit, contributes to this shutdown. RpS3a is consistently expressed in females of C. pipiens that do not enter diapause, but in females programmed for diapause, expression of the rpS3a transcript is dramatically reduced for a brief period in early diapause (7-10 days after adult eclosion). RNA interference directed against rpS3a in nondiapausing females arrested follicle development, mimicking the diapause state. The effect of the dsRNA injection faded within 10 days, allowing the follicles to grow again, thus the suppression of rpS3a caused by RNAi did not permanently block ovarian development, implying that a brief suppression of rpS3a is not the only factor contributing to the diapause response. The arrest in development that we observed in dsRNA-injected females could be reversed with a topical application of juvenile hormone III, an endocrine trigger known to terminate diapause in this species. Though we speculate that many genes contribute to the diapause syndrome in C. pipiens, our results suggest that a shut down in the expression of rpS3a is one of the important components of this developmental response.
Insect Molecular Biology 10/2009; 19(1):27-33. · 2.53 Impact Factor
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ABSTRACT: The cDNA encoding beta-tubulin in the mosquito Culex pipiens has high similarity with the beta-tubulins reported in other insects. In this study, we examine expression of this gene and microtubule abundance in relation to diapause and low temperature. While non-diapausing mosquitoes express beta-tubulin highly in their thoracic muscles, expression is quite low during adult diapause. The abundance of microtubules was also much lower in flight muscles of diapausing adults than in flight muscles from non-diapausing individuals, as confirmed by laser confocal microscopy of tubulins stained using indirect immunofluorescence. Low temperatures decreased microtubule abundance in midguts of non-diapausing mosquitoes, but microtubule abundance in diapausing mosquitoes was already low and remained unchanged by low temperature exposure. Overall, pixel intensity averages were higher in the flight muscles than in the midguts, and again low temperatures decreased microtubule abundance in the flight muscles of non-diapausing females, while levels remained consistently low in diapausing females. These results clearly indicate that a decrease in microtubule abundance is evoked both by the programming of diapause and, in non-diapausing females, by exposure to low temperatures. Quite possibly the reduced microtubule abundance in the flight muscles and reduced expression of beta-tubulin are functionally correlated to the reduction in flight activity that is associated with low temperature and diapause.
Insect Molecular Biology 07/2009; 18(3):295-302. · 2.53 Impact Factor
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ABSTRACT: Short day-length is used to programme adult diapause in the mosquito, Culex pipiens. The downstream endocrine event that halts ovarian maturation is a shut-down in juvenile hormone (JH) production, and recent evidence suggests that the insulin signalling pathway may be a key upstream player in executing this developmental arrest. Genes encoding insulin-like peptides-1, -2 and -5 were identified in C. pipiens, and we report that transcript levels of insulin-like peptides-1 and -5 were significantly lower in diapausing females than in their nondiapausing counterparts. Genes encoding both insulin-like peptides-1 and -5 were suppressed using RNA interference in mosquitoes programmed for nondiapause, and ovarian maturation was monitored. Knocking down insulin-like peptide-1 with RNAi in nondiapausing mosquitoes resulted in a cessation of ovarian development akin to diapause, and this arrest in development could be reversed with an application of JH. Knocking down insulin-like peptide-5 did not alter ovarian development. These results are consistent with a role for insulin-like peptide-1 in the signalling pathway leading from the perception of short day-lengths to the shut-down in JH production that characterizes adult diapause in C. pipiens.
Insect Molecular Biology 07/2009; 18(3):325-32. · 2.53 Impact Factor
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ABSTRACT: Rapid cold hardening (RCH) refers to the enhanced cold tolerance acquired by a brief exposure to a moderately low temperature. Although ecological aspects of this response have been well documented in insects, less is known about the physiological and biochemical mechanisms elicited by RCH. In this study we used two-dimensional electrophoresis to detect differences in brain protein abundance in pharate adults of the flesh fly Sarcophaga crassipalpis, in response to a 2 h RCH exposure at 0 degrees C. Fourteen high abundance proteins that responded to RCH were selected for mass spectrometric identification. Three proteins that increased in abundance during RCH included ATP synthase subunit alpha, a small heat shock protein (smHsp), and tropomyosin-1 isoforms 33/34. Eleven proteins that decreased in abundance or were missing following RCH included several proteins involved in energy metabolism, protein degradation, transcription, actin binding, and cytoskeleton organization. That several proteins increased in abundance during RCH underscores the dynamics of the RCH mechanism and suggests that more than one physiological response likely contribute to RCH. The increase in ATP synthase suggests an elevation of ATP during RCH, and the smHsp increase suggests that at least one of the Hsps is actually mobilized during RCH, rather than after RCH as previously assumed.
Insect Molecular Biology 10/2008; 17(5):565-72. · 2.53 Impact Factor
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ABSTRACT: Most molecular work on insect diapause has focused on the expression of unique diapause transcripts, rather than the protein products. Here we present results from a proteomic comparison of diapausing and nondiapausing pupal brains. Proteins extracted from diapausing pupal brains of the flesh fly Sarcophaga crassipalpis were separated by two-dimensional gel electrophoresis and compared with those from nondiapausing pupal brains. Unique proteins and proteins present at different levels of abundance in diapausing and nondiapausing brains were identified by Nano-LC/MS/MS (capillary-liquid chromatography-nanospray tandem mass spectrometry). With this approach and Coomassie staining, we detected 37 diapause-unique or upregulated (> or = 2x) proteins, and 43 proteins that were downregulated or not present in diapause. Heat shock proteins (Hsp70 and several small Hsps) were among the most conspicuous brain proteins present in higher amounts during diapause. Brain proteins that were less abundant in diapause included phosphoenolpyruvate synthase, fatty acid binding protein, EG0003.7, and an endonuclease. Our 2-D proteome maps included several additional unknown proteins that were more abundant in either the diapause or nondiapause brains. While the mRNAs encoding some of these proteins (e.g. Hsps) were previously known to be associated with diapause, the other proteins were not known to be linked to diapause, thus suggesting that the proteomic approach nicely supplements the work done at the transcript level.
Journal of Insect Physiology 04/2007; 53(4):385-91. · 2.24 Impact Factor
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ABSTRACT: 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.
Journal of Comparative Physiology B 03/2007; 177(2):205-15. · 1.97 Impact Factor
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American Journal of Tropical Medicine and Hygiene. 01/2007; 77(5):67-67.
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ABSTRACT: Distinct differences in the temporal expression patterns of genes associated with pupal diapause were noted in the flesh fly, Sarcophaga crassipalpis. The first change observed was a decline in expression of the gene encoding heat shock protein 90 (hsp90) 2 days after pupariation (1 day before the pupa reaches the phanerocephalic stage characteristic of diapause). In contrast, hsp23 and hsp70 transcripts were undetectable in nondiapause samples and d1-d4 diapause-programmed pupae, but were up-regulated just after the start of diapause, 5 days after pupariation. An increase of glycerol content in diapausing pupae was also noted at the start of diapause. The gene encoding proliferating cell nuclear antigen (pcna) was diapause down-regulated, and this occurred in two phases, with the first decline in expression 7 days after pupariation and a second decline in the level of expression on day 14. For pupae held at 20 degrees C for 20 days and transferred to 10 degrees C, diapause ended after 90-100 days at the lower temperature. However, pupae remained in a state of post-diapause quiescence (d100-d150) and sustained diapause-like hsp and pcna expression patterns until adult development was initiated. Glycerol concentrations and survival declined during the post-diapause phase. This study suggests a distinct sequence in the pattern of gene expression at the onset of diapause, but the genes we have monitored do not contribute to the switch to covert developmental potential at the transition from diapause to post-diapause quiescence.
Journal of Insect Physiology 07/2005; 51(6):631-40. · 2.24 Impact Factor
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ABSTRACT: cDNAs encoding prothoracicotropic hormone (PTTH) and diapause hormone (DH) were isolated from the tobacco budworm, Heliothis virescens (Hvi). Hvi-PTTH cDNA reveals key structural features known from other PTTHs, yet there is a > 30% amino acid difference between the PTTH sequences found in this noctuid when compared with the PTTHs known from Bombycoidea. Hvi-DH-PBAN cDNA encodes a precursor protein including a DH-like peptide, pheromone biosynthesis-activating neuropeptide (PBAN) and three additional neuropeptides with an FXPRL sequence at the C terminus. PTTH and DH-PBAN transcripts are most highly expressed in the brain and subesophageal ganglion (SG), respectively. Expression of both the PTTH and the DH-PBAN transcripts is high in larvae and remains high in nondiapausing pupae, but in larvae programmed for pupal diapause, expression declines sharply at the onset of larval wandering behaviour and remains low during pupal diapause. This pattern implies that both of these genes are shut down during diapause. These results are not consistent with a role for DH in promoting the entry into diapause as noted in Bombyx mori. Instead, the higher expression of DH in nondiapausing pupae suggests a possible role for DH in promoting continuous development. The injection of DH into diapausing pupae did indeed successfully terminate diapause, thus suggesting a possible new role for this neuropeptide.
Insect Molecular Biology 11/2003; 12(5):509-16. · 2.53 Impact Factor
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ABSTRACT: During the embryonic (pharate first instar) diapause of the gypsy moth, Lymantria dispar, a 55 kDa protein is highly up-regulated in the gut. We now identify that protein as hemolin, an immune protein in the immunoglobulin superfamily. We isolated a gypsy moth hemolin cDNA and demonstrated a high degree of similarity with hemolins from three other moth species. Hemolin mRNA levels increased at the time of diapause initiation and remained high throughout the mandatory period of chilling required to terminate diapause in this species, and then dropped in late diapause. This mRNA pattern reflects the pattern of protein synthesis. These results suggest that hemolin is developmentally up-regulated in the gut during diapause. Diapause in this species can be prevented using KK-42, an imidazole derivative known to inhibit ecdysteroid biosynthesis, and gypsy moths treated in this manner failed to elevate hemolin mRNA. Conversely, this diapause appears to be initiated and maintained by the steroid hormone, 20-hydroxyecdysone, and the addition of 20-hydroxyecdysone to the culture medium elevated hemolin mRNA in the gut. Our results thus indicate a role for 20-hydroxyecdysone in the elevation of hemolin mRNA during diapause. Presumably, hemolin functions to protect the gypsy moth from microbial infection during its long, overwintering diapause.
Insect Biochemistry and Molecular Biology 12/2002; 32(11):1457-67. · 3.25 Impact Factor
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ABSTRACT: Heat-shock protein 23 (hsp23) and hsp70 are both known to be strongly up-regulated during pupal diapause in the flesh fly Sarcophaga crassipalpis. This prompted us to investigate whether hsp90 was also up-regulated during diapause. To test this possibility, we developed a partial clone of a hsp90 family member for use as a probe in Northern blot hybridization. Both high and low temperature exposure up-regulated hsp90 transcripts in nondiapausing individuals. In contrast to hsp23 and hsp70, hsp90 was down-regulated following entry into diapause, and returned to prediapause levels after diapause termination. The response of hsp90 to heat shock and cold shock remained intact during diapause: both shocks evoked elevated expression. The results indicate differential regulation of hsps during diapause and in response to thermal injury inflicted on diapausing pupae.
Insect Molecular Biology 01/2001; 9(6):641-5. · 2.53 Impact Factor
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ABSTRACT: We have isolated and sequenced a 1308bp clone from a pupal brain cDNA library of the flesh fly, Sarcophaga crassipalpis, showing 97% amino acid (aa) sequence similarity to Ceratitis capitata 60S acidic ribosomal protein P0 (CcP0) and 93% aa sequence similiarity to Drosophila melanogaster P0 (DmP0). DmP0 is a multifunctional protein necessary for efficient protein translation of the 60S ribosome as well as DNA repair via AP3 endonuclease activity. In this study, we observed that S. crassipalpis P0 (ScP0) is cyclically regulated throughout the fly's overwintering pupal diapause. Expression of ScP0 cycles out of phase with the 4day cycles of O(2) consumption: the peak day of O(2) consumption is characterized by low ScP0 expression, while high expression is noted during the trough of the O(2) consumption cycle. The O(2) cycles, which are in turn driven by cycles of juvenile hormone (JH), can be eliminated by application of a JH analog (JHA). Pupae rendered acyclic with a JHA application consume O(2) at a constant high rate and ScP0 is consistently downregulated. Our findings thus suggest that the cyclic nature of ScP0 regulation during pupal diapause is linked to the JH-mediated metabolic cycles characteristic of this species.
Gene 10/2000; 255(2):381-8. · 2.34 Impact Factor
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ABSTRACT: Partial clones of the Sarcophaga crassipalpis heat shock protein 70 (hsp70) and of heat shock cognate 70 (hsc70) were developed by RT-PCR and library screening respectively. These clones were used to probe total RNA northern blots for the expression of transcripts in response to high and low temperature stress and in conjunction with the entry into an overwintering pupal diapause. In nondiapausing individuals, hsp70 was highly expressed in response to a 40 degrees C heat shock, while hsc70 was unaffected by the heat stress. In contrast, both hsp70 and hsc70 were upregulated in nondiapausing flies following a -10 degrees C cold shock. In diapausing pupae, hsp70 was highly upregulated during diapause, even at a non-stress temperature of 20 degrees C. Upregulation was initiated at the onset of diapause and persisted throughout diapause. During diapause, heat shock did not further elevate the level of hsp70 expression. Within 12 h after diapause was terminated, hsp70 ceased to be expressed. The expression of hsc70 was unaltered by diapause. The developmental regulation of hsp70 in relation to diapause suggests a critical role for this stress protein during insect dormancy.
Insect Biochemistry and Molecular Biology 07/2000; 30(6):515-21. · 3.25 Impact Factor
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ABSTRACT: A diapause upregulated cDNA clone was isolated from a cDNA library generated from brain mRNA of diapausing Sarcophaga crassipalpis pupae. The clone hybridized to a 1600 bp transcript on a northern blot. The insert is 823 bp in length, has a tentative open reading frame of 615 bp, and codes for a 23 kDa protein. The clone has a high level of identity at the amino acid level with the four small heat shock proteins of Drosophila melanogaster. Northern analysis revealed no detectable expression of the transcript in diapause- or nondiapause-programmed wandering larvae, and only trace expression in nondiapausing pupae. But, the transcript was highly expressed beginning at the onset of diapause and continuing throughout diapause. Expression promptly decreased when diapause was terminated. In nondiapausing individuals the transcript was highly expressed in response to cold shock or heat shock, but temperature stress did not cause greater expression in diapausing pupae. The results imply that expression of this small heat shock protein, a response elicited by temperature stress in nondiapausing individuals, is a normal component of the diapause syndrome. The upregulation of this gene during diapause suggests that it plays an essential role during this overwintering developmental arrest.
Insect Biochemistry and Molecular Biology 10/1998; 28(9):677-82. · 3.25 Impact Factor
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ABSTRACT: We report the isolation and sequencing of a 1326 bp cDNA fragment encoding the cell-cycle proliferation protein ScPCNA from the flesh fly, Sarcophaga crassipalpis. The amino acid (aa) sequence shows 91% and 79% identity to Drosophila melanogaster and Bombyx mori proliferating cell nuclear antigen (PCNA), respectively. The coding sequence is interrupted by a single intron of 60 bp, resulting in a deduced aa sequence of 260 residues. The gene is transcribed as a single mRNA (approx. 1.2 ) as determined by Northern blot hybridization. Following a cold shock at -10 degrees C for 1 h, expression of ScPCNA decreased in S. crassipalpis whole-body mRNA, suggesting a possible cell-cycle arrest in response to a cold shock. One hour after removal from cold shock, ScPCNA transcript levels were restored to the control level. By contrast, a 1 h heat shock at 45 degrees C did not alter expression of ScPCNA.
Gene 07/1998; 215(2):425-9. · 2.34 Impact Factor
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ABSTRACT: Several cDNAs isolated from brains of diapausing pupae of the flesh fly, Sarcophaga crassipalpis, show expression patterns unique to diapause. To isolate such cDNAs a diapause pupal brain cDNA library was screened by using an elimination hybridization technique, and cDNAs that did not hybridize with cDNA probes constructed from the RNA of nondiapausing pupae were selected for further screening. The 95 clones that did not hybridize in the initial library screen were selected for further characterization. These clones were then screened against diapause and nondiapause pupal poly(A)+ Northern blots. The secondary screen identified 4 diapause-up-regulated clones, 7 diapause-down-regulated clones, 8 clones expressed equally in both diapause and nondiapause, and 75 clones without detectable expression. The diapause-up-regulated and down-regulated clones were further characterized by partial DNA sequencing and identity searches by using GenBank. Identities between our cloned cDNAs and other genes included those linked to cell cycle progression, stress responses, and DNA repair processes. The results suggest that insect diapause is not merely a shutdown of gene expression but is a unique, developmental pathway characterized by the expression of a novel set of genes.
Proceedings of the National Academy of Sciences 06/1998; 95(10):5616-20. · 9.68 Impact Factor
