Joint development in the Drosophila leg: cell movements and cell populations

Flexible joints separate the rigid sections of the insect leg, allowing them to move. In Drosophila, the initial patterning of these joints is apparent in the larval imaginal discs from which the adult legs will develop. Here, we describe the later patterning and morphogenesis of the joints, which occurs after pupariation (AP). In the tibial/tarsal joint, the apodeme insertion site provides a fixed marker for the boundary between proximal and distal joint territories (the P/D boundary). Cells on either side of this boundary behave differently during morphogenesis. Morphogenesis begins with the apical constriction of distal joint cells, about 24 h AP. Distal cells then become columnar, causing distal tissue nearest the P/D boundary to fold into the leg. In the last stage of joint morphogenesis, the proximal joint cells closest to the P/D boundary align and elongate to form a "palisade" (a row of columnar cells) over the distal joint cells. The proximal and distal joint territories are characterised by the differential organisation of cytoskeletal and extracellular matrix proteins, and by the differential expression of enhancer trap lines and other gene markers. These markers also define a number of more localised territories within the pupal joint.     

Expression of Biologically Active Crustacean Hyperglycemic Hormone (CHH) of <Emphasis Type="Italic">Penaeus monodon</Emphasis> in <Emphasis Type="Italic">Pichia pastoris</Emphasis>

Crustacean hyperglycemic hormone (CHH), molt-inhibiting hormone (MIH), and gonad-inhibiting hormone (GIH) are members of a major peptide family produced from the X-organ sinus gland complex in the eyestalk of crustaceans. This peptide family plays important roles in controlling several physiologic processes such as regulation of growth and reproduction. In this study the complementary DNA encoding a peptide related to the CHH/MIH/GIH family (so-called Pem-CMG) of the black tiger prawn Penaeus monodon was successfully expressed in the yeast Pichia pastoris under the control of the AOX1 promoter. The recombinant Pem-CMG was secreted into the culture medium using the -factor signal sequence; of Saccharomyces cerevisiae without the Glu-Ala-Glu-Ala spacer peptide. The amino terminus of the recombinant Pem-CMG was correctly processed as evidenced by amino-terminal peptide sequencing. The recombinant Pem-CMG was purified by reverse-phase high-performance liquid chromotography and used in a biological assay for CHH activity. The final yield of the recombinant Pem-CMG after purification was 260 µg/L of the culture medium. Both crude and purified recombinant Pem-CMG produced from P. pastoris showed the ability to elevate the glucose level in the hemolymph of eyestalk-ablated P. monodon, which demonstrates that Pem-CMG peptide functions as hyperglycemic hormone in P. monodon.     

Reduced seroprevalence of Kaposi's sarcoma-associated herpesvirus (KSHV), human herpesvirus 8 (HHV8), related to suppression of Anopheles density in Italy

In two formerly malarious parts of Italy, age-related seroprevalence rates of Kaposi's sarcoma-associated herpesvirus [human herpesvirus 8 (KSHV/HHV8)] were determined from local blood donors and correlated with periods of vector control during anti-malaria campaigns. In Veneto, decreased KSHV/HHV8 seroprevalence in the 1951-1955 birth cohort coincides with the peak of DDT house-spraying. In Sardinia, where larviciding augmented indoor DDT-spraying, a significant drop of KSHV/HHV8 seroprevalence between 1945 and 1950 and 1951-1955 birth cohorts (P = 0.0046) coincides with suppression of the malaria vector Anopheles labranchiae Falleroni (Diptera: Culicidae). These results are consistent with age-related association between KSHV/HHV8 seroprevalence rates in native/resident populations and the density of malaria vectors in Veneto and Sardinia. This example supports our 'promoter arthropod' hypothesis on the role of haematophagous insects [putatively blackflies (Simuliidae), sandflies (Phlebotominae) and biting midges (Ceratopogonidae), as well as mosquitoes] when their bites induce hypersensitivity and immunosuppression, potentiate KSHV/HHV8 transmission via human saliva (when insect bite lesions are licked by another person whose saliva carries the virus) and may facilitate Kaposi's sarcoma.     

Effects of mushroom size on the structure of a mycophagous arthropod community: Comparison between infracommunities with different types of resource utilization

The effects of the size of a patchy resource on the structure of a mycophagous arthropod community were examined by comparing numerical responses to the size of individual mushrooms between visitor and dweller communities. A total of 17 fungal genera in nine families were identified during the 13month survey period. A total of 35 arthropod families from nine orders were recorded, with the Hypogastruridae (Collembola) forming 97% of the number of individuals in the visitor community. The response of the visitor community (i.e. number of families, number of individuals, density per mushroom size and diversity) to mushroom size varied in each survey month according to hypogastrurid density. The response of the community composition to mushroom size also varied monthly with hypogastrurid density. In the dweller community, 12 families in three orders were recorded, and one coleopteran and five dipteran families accounted for 90% of the number of individuals. Although the density of dwellers in a mushroom varied between months, the response of the community properties to mushroom size was consistent throughout the survey period. Community composition varied monthly with mushroom size. These results suggest that the size of individual mushrooms is likely to have a greater effect on the structure of dweller communities than visitor communities. Thus, the characteristics of a patchy resource may exert different impacts on the structure of different arthropod communities utilizing the same resource, but in a different manner.     

Impact on soil-dwelling arthropods in citrus orchards of spraying horticultural mineral oil, carbaryl or methidathion

Abstract  Impacts of an n C24 horticultural mineral oil (HMO) and two synthetic insecticides (carbaryl and methidathion) on the abundance and species diversity of soil-dwelling arthropods were evaluated in two citrus orchards in the coastal region of New South Wales, Australia. In the first orchard, mature Valencia orange trees were sprayed in summer with one of HMO, carbaryl or methidathion delivered at low (2000 L/ha) or high (10 000 L/ha) volumes; the sprays were applied either once (February) or twice (December and February). HMO had no significant impact but the synthetic insecticides, irrespective of spray frequency or spray volume, significantly reduced the abundance and species diversity of the arthropods including springtails and generalist predators, such as spiders, staphylinid beetles and mesostigmatid mites. In the second orchard, blocks of Washington navel and Valencia orange trees were sprayed with either HMO or methidathion; sprays were applied twice, 2 weeks apart, in late summer (February), first at a rate of 6500 L/ha and second at 5500 L/ha. Results were similar to those in the first orchard, except that the effect of methidathion on carabid beetles and ants was not significant.     

Nonnative plant invasion increases urban vegetation structure and influences arthropod communities

Aim

Ecological theory and empirical evidence indicate that greater structural complexity and diversity in plant communities increases arthropod abundance and diversity. Nonnative plants are typically associated with low arthropod abundance and diversity due to lack of evolutionary history. However, nonnative plants increase the structural complexity of forests, as is common in urban forests. Therefore, urban forests are ideal ecosystems to determine whether structural complexity associated with nonnative plants will increase abundance and diversity of arthropods, as predicted by complexity literature, or whether structural complexity associated with nonnative plants will be depauperate of arthropods, as predicted by nonnative plant literature.

Location

We sampled 24 urban temperate deciduous and mixed forests in two cites, Raleigh, North Carolina and Newark, Delaware, in the eastern United States.

Methods

We quantified ground cover vegetation and shrub layer vegetation in each forest and created structural complexity metrics to represent total, nonnative and native understory vegetation structural complexity. We vacuum sampled arthropods from vegetation and quantified the abundance, biomass, richness and diversity of spiders and non-spider arthropods.

Results

Nonnative plants increase understory vegetation complexity in urban forests. In Raleigh and Newark, we found support for the hypotheses that dense vegetation will increase arthropod abundance and biomass, and against the hypothesis that nonnative vegetation will decrease arthropods. Urban forest arthropod abundance and biomass, but not diversity, increased with greater nonnative and native structural complexity.

Main Conclusions

Invaded urban forests may provide adequate food in the form of arthropod biomass to transfer energy to the next trophic level, but likely fail to provide ecological services and functions offered by diverse species, like forest specialists. Urban land managers should survey urban forests for nonnative and native plant communities and prioritize replacing dense nonnative plants with native species when allocating vegetation maintenance resources.     

节肢动物毒素研究进展

节肢动物（arthropod）是动物界中种类数量最多、分布范围最广的类群,现存110万~120万种。节肢动物毒素具有较强的生物学活性及独特的作用机制,其毒素分子能够作用于离子通道、细胞膜、受体和酶等靶点,影响神经、循环、免疫、肌肉等系统,从而进行快速、高效的捕食和防御。本文总结了有毒节肢动物毒素的来源、成分及作用靶点等信息,重点综述了毒素作用机制的分子基础,以及毒素参与的捕食、防御和趋避等生物学作用。     

Quantum mechanical analysis of oxygenated and deoxygenated states of hemocyanin: theoretical clues for a plausible allosteric model of oxygen binding.

Abstract: In this work with ab initio computations, we describe relevant interactions between protein active sites and ligands, using as a test case arthropod hemocyanins. A computational analysis of models corresponding to the oxygenated and deoxygenated forms of the hemocyanin active site is performed using the Density Functional Theory approach. We characterize the electron density distribution of the binding site with and without bound oxygen in relation to the geometry, which stems out of the crystals of three hemocyanin proteins, namely the oxygenated form from the horseshoe crab Limulus polyphemus, and the deoxygenated forms, respectively, from the same source and from another arthropod, the spiny lobster Panulirus interruptus. Comparison of the three available crystals indicate structural differences at the oxygen binding site, which cannot be explained only by the presence and absence of the oxygen ligand, since the geometry of the ligand site of the deoxygenated Panulirus hemocyanin is rather similar to that of the oxygenated Limulus protein. This finding was interpreted in the frame of a mechanism of allosteric regulation for oxygen binding. However, the cooperative mechanism, which is experimentally well documented, is only partially supported by crystallographic data, since no oxygenated crystal of Panulirus hemocyanin is presently available. We address the following question: is the local ligand geometry responsible for the difference of the dicopper distance observed in the two deoxygenated forms of hemocyanin or is it necessary to advocate the allosteric regulation of the active site conformations in order to reconcile the different crystal forms? We find that the difference of the dicopper distance between the two deoxygenated hemocyanins is not due to the small differences of ligand geometry found in the crystals and conclude that it must be therefore stabilized by the whole protein tertiary structure.     

Arboreal arthropod biodiversity in woodlands. II. The pattern of recovery of diversity on Melaleuca linariifolia following defaunation

This study examines the level of isolation of arthropod faunas present on specimens of the endemic woodland tree Melaleuca linariifolia by investigating the recovery of faunas after defaunation using insecticide. One tree from each of 21 pairs of trees was sprayed at the beginning of the project (early April 1994). After predetermined periods, three test trees were resprayed along with matched control trees. A total of 95 154 arthropods were collected and sorted during the project. The number of species present on the trees recovered within 16 weeks of spraying, with common species recolonizing within a fortnight. The rarer species both of mobile (Diptera) and relatively sedentary (Araneae) taxa reappeared at similar rates. Complete recovery of numbers occurred by week 8 after spraying. Evenness (as Simpson’s D) recovered over the first 2 months; however, both the number of individuals and the evenness continued to diverge from the pattern seen on the control trees until the end of the study. While the rate of movement of individuals and species was such as to provide an apparently complete set of replacement species within several months of perturbation, the structure of the community found on the trees was still seriously disrupted after 1 year. Comparison of the suites of species originally found on the trees with those found in the respray samples and the control samples showed that the set of colonizing species was no more similar to the original fauna of the tree than it was to those on the control tree. The relatively rapid colonization of the trees by a suite of rare species – not necessarily those that were on particular trees before perturbation – indicates that rarity was due neither to inability of the species to colonize the trees nor to the suitability of the trees for these species. Recovery of rare species was to a level similar to that found on the control trees. That the divergences from the controls continued (in number of individuals and in evenness), implies a definite connection between the different faunas of a tree and their partial isolation from fauna communities on other trees. Whatever the forces that maintain suites of species on each tree, it is not the ability of the species to reach and colonize trees, nor certain attributes of a tree, that make it suitable only for a particular subset of the species available. Trees are not isolated entities but neither are they part of a fully integrated community, either chronologically or spacially, and issues of scale are also likely to be important in understanding and estimating the dynamics and factors regulating biodiversity levels.     

Structure and functions of arthropod proteasomes

Recent work on structural/functional relationships in arthropod proteasomes is reviewed. Taking advantage of our ability to induce a stable, proteolytically-active conformation of the lobster proteasome, the structures of basal and heat-activated complexes were probed with exogenous proteases. Increased sensitivity to chymotrypsin and trypsin showed that heat activation induced a more open conformation, allowing entry of large substrates into the catalytic chamber. In Drosophila, the effects of two developmental mutant alleles (DTS-7 and DTS-5) encoding proteasome subunits (Z and C5, respectively) on the subunit composition and catalytic activities of the enzyme were examined. Both qualitative and quantitative differences in compositions between wild-type (+/+) and heterozygotes (+/DTS) indicated that incorporation of mutant subunits alters post-translational modifications of the complex. Catalytic activities, however, were similar, which suggests that the developmental defect involves other proteasome properties, such as intracellular localization and/or interactions with endogenous regulators. A hypothetical model in which DTS subunits act as poison subunits is presented.