Ecdysis of decapod crustaceans is associated with a dramatic release of crustacean cardioactive peptide into the haemolymph.
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On the basis of detailed analyses of morphological characteristics and behavioural events associated with ecdysis in a crab (Carcinus maenas) and a crayfish (Orconectes limosus), a comprehensive substaging system has been introduced for the ecdysis stage of the moult cycle of these decapod crustaceans. In a remarkably similar stereotyped ecdysis sequence in both species, a passive phase of water uptake starting with bulging and rupture of thoracoabdominal exoskeletal junctions is followed by an active phase showing distinct behavioural changes involved in the shedding of the head appendages, abdomen and pereiopods. Together with an enzyme immunoassay for crustacean cardioactive peptide (CCAP), the substaging has been used to demonstrate a large, rapid and reproducible peak in haemolymph CCAP levels (increases of approximately 30-fold in the crab and more than 100-fold in the crayfish compared with intermoult titres) during the later stages of active ecdysis. We suggest that the release of CCAP (accumulated in late premoult) from the crab pericardial organs or the crayfish ventral nerve cord accounts for many of the changes in behaviour and physiology seen during ecdysis and that this neurohormone is likely to be of critical importance in crustaceans and other arthropods. (+info)
The physiology of salinity tolerance in larvae of two species of Culex mosquitoes: the role of compatible solutes.
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We investigated the physiological basis for differences in salinity tolerance ranges in mosquito larvae of the genus Culex. We examined the response of larvae of C. quinquefasciatus, a freshwater obligate, and C. tarsalis, a euryhaline osmoconformer, following transfer from fresh water to 34% sea water. Hemolymph Na(+) and Cl(-) levels increased similarly in both species, indicating that ion regulation does not differ under these conditions. C. quinquefasciatus responded to increased environmental salinity with increased hemolymph levels of serine, but suffered a significant reduction in levels of trehalose. C. tarsalis responded to increased environmental salinity with increased hemolymph levels of both proline and trehalose. When C. tarsalis larvae were held in 64% sea water, which C. quinquefasciatus larvae cannot tolerate, hemolymph proline and trehalose were accumulated approximately 50-fold and twofold, respectively, relative to freshwater values. We found that proline serves as both an intra- and extracellular compatible solute in C. tarsalis, the first such circumstance documented in an animal in response to increased environmental salinity. Analyses of the acute responses of the two species to an increase in salinity (from 30% to 50% sea water) indicate that larvae of C. tarsalis are able to volume-regulate via drinking and to attenuate increases in hemolymph NaCl concentration using unknown mechanisms during large, rapid increases in salinity. (+info)
Regulation of compatible solute accumulation in larvae of the mosquito Culex tarsalis: osmolarity versus salinity.
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In this study, we demonstrate that two of the osmolytes utilized in the osmoconforming strategy of larval Culex tarsalis are regulated by two fundamentally different signals. When the external osmolality was increased using salinity (sea salts), hemolymph NaCl, proline and trehalose concentrations increased significantly. When sorbitol was used to increase the external osmolality without an elevation in salt concentration, hemolymph NaCl and proline concentrations decreased, whereas hemolymph trehalose concentration increased. The results suggest that proline accumulation was cued by increases in salinity, whereas trehalose levels followed increases in osmolality. Interestingly, we found that C. tarsalis larvae accumulated the exogenous sorbitol in the hemolymph in an osmoconforming manner. We conducted further studies in which changes in hemolymph NaCl concentrations were manipulated using changes in environmental salinity. The results suggested that hemolymph proline accumulation was cued by the proximal signal of hemolymph NaCl levels. Regardless of which solute (sea salts, sorbitol or mixtures thereof) was used to raise the external osmolality, trehalose accumulation tracked the increase in total osmolality of the medium. These findings indicate that the synthesis and accumulation of these two osmolytes are regulated by two independent signals. (+info)
Viresin. A novel antibacterial protein from immune hemolymph of Heliothis virescens pupae.
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Immune hemolymph was collected from fifth instar larvae and 1-day-old pupae of Heliothis virescens after injection of prepupae with live Enterobacter cloacae. Induction of antibacterial activity against Escherichia coli K12 D31 was 7.5 times greater in pupal than in larval immune hemolymph. Lysozyme activity of immune pupal hemolymph against Micrococcus lysodeikticus was 11 times greater when compared with lysozyme activity of immune larval hemolymph. Early pupal immune response with regard to antibacterial activity was much greater than larval immune response in H. virescens. Normal pupal hemolymph showed an increase in antibacterial activity and lysozyme that was induced during metamorphosis. Antibacterial protein was isolated together with lysozyme by gel filtration chromatography and then separated from lysozyme by sequential electrophoresis with a native acid gel and SDS gel. Molecular mass of antibacterial protein was estimated to be 12 kDa. The N-terminal amino acid sequence of 12-kDa protein was different from those of antibacterial molecules found in other insects and has not been identified before. A sample containing 12-kDa protein was negative for immunoblotting with anti-synthetic cecropin B antibody. We have named the novel 12-kDa antibacterial protein viresin. Viresin showed antibacterial activity against several Gram-negative bacteria including E. cloacae but not against Gram-positive bacteria. (+info)
Modifications of seizure susceptibility in Drosophila.
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In a given population, certain individuals are much more likely to have seizures than others. This increase in seizure susceptibility can lead to spontaneous seizures, such as seen in idiopathic epilepsy, or to symptomatic seizures that occur after insults to the nervous system. Despite the frequency of these seizure disorders in the human population, the genetic and physiological basis for these defects remains unclear. The present study makes use of Drosophila as a potentially powerful model for understanding seizure susceptibility in humans. In addition to the genetic and molecular advantages of using Drosophila, it has been found that seizures in Drosophila share much in common with seizures seen in humans. However, the most powerful aspect of this model lies in the ability to accurately measure seizure susceptibility across genotypes and over time. In the current study seizure susceptibility was quantified in a variety of mutant and wild-type strains, and it was found that genetic mutations can modulate susceptibility over an extremely wide range. This genetic modulation of seizure susceptibility apparently occurs without affecting the threshold of individual neurons. Seizure susceptibility also varied depending on the experience of the fly, decreasing immediately after a seizure and then gradually increasing over time. A novel phenomenon was also identified in which seizures are suppressed after certain high-intensity stimuli. These results demonstrate the utility of Drosophila as a model system for studying human seizure disorders and provide insights into the possible mechanisms by which seizure susceptibility is modified. (+info)
Density-dependent prophylaxis in the mealworm beetle Tenebrio molitor L. (Coleoptera: Tenebrionidae): cuticular melanization is an indicator of investment in immunity.
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If there are costs involved with the maintenance of pathogen resistance, then higher investment in this trait is expected when the risk of pathogenesis is high. One situation in which the risk of pathogenesis is elevated is at increased conspecific density. This paper reports the results of a study of density-dependent polyphenism in pathogen resistance and immune function in the mealworm beetle Tenebrio molitor. Beetles reared at high larval densities showed lower mortality when exposed to a generalist entomopathogenic fungus and a higher degree of cuticular melanization than those reared solitarily. The degree of cuticular melanization was a strong indicator of resistance, with darker beetles being more resistant than lighter ones regardless of rearing density. No differences were found between rearing densities in the levels of phenoloxidase, an enzyme key to the insect immune response. The results show that pathogen resistance is phenotypically plastic in T. molitor, suggesting that the maintenance of this trait is costly. (+info)
Genetics of mosquito vector competence.
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Mosquito-borne diseases are responsible for significant human morbidity and mortality throughout the world. Efforts to control mosquito-borne diseases have been impeded, in part, by the development of drug-resistant parasites, insecticide-resistant mosquitoes, and environmental concerns over the application of insecticides. Therefore, there is a need to develop novel disease control strategies that can complement or replace existing control methods. One such strategy is to generate pathogen-resistant mosquitoes from those that are susceptible. To this end, efforts have focused on isolating and characterizing genes that influence mosquito vector competence. It has been known for over 70 years that there is a genetic basis for the susceptibility of mosquitoes to parasites, but until the advent of powerful molecular biological tools and protocols, it was difficult to assess the interactions of pathogens with their host tissues within the mosquito at a molecular level. Moreover, it has been only recently that the molecular mechanisms responsible for pathogen destruction, such as melanotic encapsulation and immune peptide production, have been investigated. The molecular characterization of genes that influence vector competence is becoming routine, and with the development of the Sindbis virus transducing system, potential antipathogen genes now can be introduced into the mosquito and their effect on parasite development can be assessed in vivo. With the recent successes in the field of mosquito germ line transformation, it seems likely that the generation of a pathogen-resistant mosquito population from a susceptible population soon will become a reality. (+info)
A beta1,3-glucan recognition protein from an insect, Manduca sexta, agglutinates microorganisms and activates the phenoloxidase cascade.
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Pattern recognition proteins function in innate immune responses by binding to molecules on the surface of invading pathogens and initiating host defense reactions. We report the purification and molecular cloning of a cDNA for a 53-kDa beta1,3-glucan-recognition protein from the tobacco hornworm, Manduca sexta. This protein is constitutively expressed in fat body and secreted into hemolymph. The protein contains a region with sequence similarity to several glucanases, but it lacks glucanase activity. It binds to the surface of and agglutinates yeast, as well as gram-negative and gram-positive bacteria. Beta1,3-glucan-recognition protein in the presence of laminarin, a soluble glucan, stimulated activation of prophenoloxidase in plasma, whereas laminarin alone did not. These results suggest that beta1,3-glucan-recognition protein serves as a pattern recognition molecule for beta1,3-glucan on the surface of fungal cell walls. After binding to beta1,3-glucan, the protein may interact with a serine protease, leading to the activation of the prophenoloxidase cascade, a pathway in insects for defense against microbial infection. (+info)