Mechanisms of midgut remodeling: juvenile hormone analog methoprene blocks midgut metamorphosis by modulating ecdysone action

In holometabolous insects such as mosquito, Aedes aegypti, midgut undergoes remodeling during metamorphosis. Insect metamorphosis is regulated by several hormones including juvenile hormone (JH) and 20-hydroxyecdysone (20E). The cellular and molecular events that occur during midgut remodeling were investigated by studying nuclear stained whole mounts and cross-sections of midguts and by monitoring the mRNA levels of genes involved in 20E action in methoprene-treated and untreated Ae. aegypti. We used JH analog, methoprene, to mimic JH action. In Ae. aegypti larvae, the programmed cell death (PCD) of larval midgut cells and the proliferation and differentiation of imaginal cells were initiated at about 36h after ecdysis to the 4th instar larval stage (AEFL) and were completed by 12h after ecdysis to the pupal stage (AEPS). In methoprene-treated larvae, the proliferation and differentiation of imaginal cells was initiated at 36h AEFL, but the PCD was initiated only after ecdysis to the pupal stage. However, the terminal events that occur for completion of PCD during pupal stage were blocked. As a result, the pupae developed from methoprene-treated larvae contained two midgut epithelial layers until they died during the pupal stage. Quantitative PCR analyses showed that methoprene affected midgut remodeling by modulating the expression of ecdysone receptor B, ultraspiracle A, broad complex, E93, ftz-f1, dronc and drice, the genes that are shown to play key roles in 20E action and PCD. Thus, JH analog, methoprene acts on Ae. aegypti by interfering with the expression of genes involved in 20E action resulting in a block in midgut remodeling and death during pupal stage.

Comparative analysis of the development of the mandibular salivary glands and the labial silk glands in the mulberry silkworm, Bombyx mori

The mulberry silkworm, Bombyx mori has a pair of salivary glands arising from the mandibular segment, in addition to the labial silk glands which are generally considered as modified salivary glands. Here we report the characterization of salivary glands and the comparative gene expression profiling of the silk and salivary glands. The two independent salivary glands made up by 330 cells, grow about 1000 fold during larval development. These individual glands extend up to the T(1) thoracic segment unlike silk glands with fused anterior ends and extending up to the caudal region. The salivary glands also undergo endomitosis resembling the silk glands. The B. mori homologue of the homeotic gene Deformed (BmDfd) was expressed in the mandibular and maxillary segments in stage 17 embryo and got localized to the centre of the mandibular segment at stage 18 to form the salivary gland placodes. The expression was also seen in the distal ends of the leg appendages after blastokinesis (stage 22). Only low variations in BmDfd expression ranging from 1.6 to 2.1 fold were apparent during embryonic development. BmDfd expression was observed in the salivary glands all through the larval instars but not in the silk glands. The transcription factor, Forkhead and the segment polarity gene, Wingless were expressed throughout the salivary glands, the latter confirming the absence of physiological compartmentation within these glands unlike the silk glands. The expression of Amylase and Fibrohexamerin was restricted to the salivary and silk glands, respectively and therefore, served as molecular markers for these tissues.

Biochemical and immunological properties of cytokines conjugated to dendritic polymers

Here we describe a post-translational modification of SC-63032, a variant of the species restricted, multi-lineage hematopoeitic factor human interleukin-3 (hIL-3). We have made two new dendritic polymer (polyamidoamine or PAMAM dendrimers, generation 5)-SC-63032 bioconjugates. Using two distinct chemistries (one of which is novel to this work), we achieved site-specific conjugation with respect to the amino acid in the proteins ligated to the dendrimers. In both bioconjugates, conjugated cytokine maintains its ability to bind the hIL-3 alpha receptor subunit, but is significantly (about 10-fold) less potent in inducing hIL-3 dependent in vitro cell proliferation than is the free cytokine. In vivo data indicates that conjugation decreases the immunogenicity of the conjugated cytokine modestly. In the absence of pharmacokinetic or biodistribution effects associated with the bioconjugates that increase their potency in vivo (which can only be tested in a higher primate, due to the species restriction of hIL-3 and its derivatives), these immune mitigation effects may be too small to be therapeutically significant. Though unmodified PAMAM dendrimers fail to elicit an antibody response in mice, protein conjugation to dendrimers haptenizes them, and a dendrimer-specific antibody response is produced. In toto, the principal limitation of the dendrimer-cytokine bioconjugates herein is in their reduced receptor affinity and potency in vitro. Were the in vivo potency of the bioconjugates to parallel the in vitro potency of the conjugates reported here, it is likely that particular dendrimer bioconjugates could not justify their higher costs of goods relative to the parent SC-63032 molecule, though retention of SC-63032 biological activities in conjugates suggests that other cytokine-dendrimer bioconjugates may be bioactive. This is good news to the nanotechnology community, in as much as PAMAM dendrimers are among the monodisperse polymeric nanomaterials available, and these results show that they can be used successfully in conjugates to bioactive proteins.

Quantum Phase Transition of a Magnet in a Spin Bath

The excitation spectrum of a model magnetic system, LiHoF4, was studied with the use of neutron spectroscopy as the system was tuned to its quantum critical point by an applied magnetic field. The electronic mode softening expected for a quantum phase transition was forestalled by hyperfine coupling to the nuclear spins. We found that interactions with the nuclear spin bath controlled the length scale over which the excitations could be entangled. This generic result places a limit on our ability to observe intrinsic electronic quantum criticality.

Rydberg electron transfer to C6H5NO2: lifetimes and characteristics of the product C6H5NO2- ions

The nature of electron binding in C6H5NO2- ions produced by Rydberg electron transfer in K(np)C6H5NO2 collisions is investigated through measurements of the number and the lifetimes of the product ions and their dependence on Rydberg atom velocity and principal quantum number n in the range 12 <or approximately n <or approximately 30. The data are interpreted by comparison to results obtained using well-known dipole-bound and valence-bound anions. At high n direct capture into valence-bound states with a lifetime of approximately 1.6 ms is observed. At low n the data suggest that, while direct capture into valence-bound states is still possible, the majority of the observed C6H5NO2- ions result from the onset of a second reaction channel that involves the formation of a dipole-bound "doorway" state that rapidly evolves into a state with predominantly valence-bound character. These findings are discussed in the light of earlier work on electron binding to C6H5NO2.

Dynamics of Rydberg electron transfer to CH3CN: velocity dependent studies

The dynamics of free-ion production through electron transfer in K(np)/CH3CN collisions are examined through measurements using velocity-selected Rydberg atoms. The data show that Rydberg electron transfer leads to the creation of two groups of dipole-bound CH3CN- ions, one long lived (tau>85 micros), the other short lived (tau<1 micros). The velocity dependences associated with the production of both groups of ions are similar, the ion formation rate decreasing markedly with decreasing Rydberg atom velocity, principally as a consequence of postattachment electrostatic interactions between the product ions. The results are in reasonable accord with the predictions of a Monte Carlo collision model that considers the effect of crossings between the diabatic potential curves for the covalent K(np)/CH3CN system and the K+/CH3CN- ion pair. This model also accounts for the relatively small reaction rate constants, approximately 0.5-1.0 x 1.0(-8) cm(3) s(-1), associated with the formation of long-lived CH3CN- ions. No velocity dependence in the lifetime of the CH3CN- ions is observed.

Beta-Cell sparing in transplanted islets by vascular endothelial growth factor

We have reported that vascular endothelial growth factor (VEGF) promotes the revascularization of transplanted islets, thereby reducing the initial number required to prevent diabetes. The present study was undertaken to assess other mechanisms of beta-cell sparing by VEGF. For in vitro studies, islets were cultured for 14 days with versus without 20 ng/mL VEGF. Viability, necrosis, and apoptosis were examined by specific staining (Alcein AM, propidium iodide, and annexin/phosphatidylserine). The effects of VEGF on islets were also examined in a proteomic study. In vivo streptozotocin-treated diabetic Lewis rats received 1000 Lewis or Sprague-Dawley islets beneath the renal capsule. Oxygen levels at the transplant site were monitored by a Clark-type oxygen electrode. Fasting blood glucose served as an indicator of islet survival and function. VEGF enhanced oxygen levels at the transplant site. Syngeneic recipients were euglycemic for over 6 months, whereas control islets failed within 30 to 60 days. VEGF prevented allograft rejection for over 14 days, whereas controls were rejected within 6 to 7 days. Immunostaining suggested that VEGF inhibited the presentation of MHC II antigen and promoted islet survival by the inhibition of necrosis and apoptosis. Our proteomic study suggested VEGF preserved systems required for cellular preservation (heat shock proteins) and insulin secretion. VEGF promotes the preservation of isolated and transplanted islets by a variety of mechanisms, including enhanced oxygenation and inhibition of immune rejection, necrosis, and apoptosis. The provision of exogenous VEGF may be a useful adjunct to islet transplantation.

Coherent spin oscillations in a disordered magnet

Most materials freeze when cooled to sufficiently low temperature. We find that magnetic dipoles randomly distributed in a solid matrix condense into a spin liquid with spectral properties on cooling that are the diametric opposite of those for conventional glasses. Measurements of the nonlinear magnetic dynamics in the low-temperature liquid reveal the presence of coherent spin oscillations composed of hundreds of spins with lifetimes of up to 10 seconds. These excitations can be labeled by frequency and manipulated by the magnetic fields from a loop of wire and can permit the encoding of information at multiple frequencies simultaneously.