Localized recruitment and activation of RhoA underlies dendritic spine morphology in a glutamate receptor-dependent manner

Actin is the major cytoskeletal source of dendritic spines, which are highly specialized protuberances on the neuronal surface where excitatory synaptic transmission occurs (Harris, K.M., and S.B. Kater. 1994. Annu. Rev. Neurosci. 17:341-371; Yuste, R., and D.W. Tank. 1996. Neuron. 16:701-716). Stimulation of excitatory synapses induces changes in spine shape via localized rearrangements of the actin cytoskeleton (Matus, A. 2000. Science. 290:754-758; Nagerl, U.V., N. Eberhorn, S.B. Cambridge, and T. Bonhoeffer. 2004. Neuron. 44:759-767). However, what remains elusive are the precise molecular mechanisms by which different neurotransmitter receptors forward information to the underlying actin cytoskeleton. We show that in cultured hippocampal neurons as well as in whole brain synaptosomal fractions, RhoA associates with glutamate receptors (GluRs) at the spine plasma membrane. Activation of ionotropic GluRs leads to the detachment of RhoA from these receptors and its recruitment to metabotropic GluRs. Concomitantly, this triggers a local reduction of RhoA activity, which, in turn, inactivates downstream kinase RhoA-specific kinase, resulting in restricted actin instability and dendritic spine collapse. These data provide a direct mechanistic link between neurotransmitter receptor activity and the changes in spine shape that are thought to play a crucial role in synaptic strength.     

Induction of heme oxygenase-1 inhibits NAD(P)H oxidase activity by down-regulating cytochrome b558 expression via the reduction of heme availability

Heme-oxygenase-1 (HO-1), the rate-limiting enzyme of heme degradation, has powerful anti-oxidant properties related to the production of the reactive oxygen species scavenger bilirubin. However, some data suggest that HO-1 could also inhibit the cellular production of reactive oxygen species. Therefore, we investigated whether the anti-oxidant properties of HO-1 could be mediated by modulation of the activity and/or expression of the heme-containing NAD(P)H oxidase, the main source of the superoxide anion (O(2)(-)) in phagocytic cells. Increasing HO-1 expression in RAW 264.7 macrophages effectively decreased NAD(P)H oxidase activity and expression of gp91(phox), its heme-containing catalytic component, because of deficient protein maturation and increased degradation. Loading cells with heme reversed the decrease in O(2)(-) production and gp91(phox) expression induced by HO-1 overexpression. Similar results were obtained in vivo in rat alveolar macrophages after pharmacological modulation of HO-1 expression or activity. These results show that a decrease in heme content due to HO-1 activation limits heme availability for maturation of the gp91(phox) subunit and assembly of the functional NAD(P)H oxidase. This study provides a new mechanism to explain HO-1 anti-oxidant properties.     

Irradiation of Anastrepha obliqua (Diptera: Tephritidae) revisited: optimizing sterility induction

The effects of irradiation doses increasing from 0 to 100 Gy (1 Gy is energy absorbed in J kg(-1) of irradiated material) on fertility, flight ability, survival, and sterile male mating performance were evaluated for mass-reared Anastrepha obliqua (Macquart). High sterility values (> 98.2%) for irradiated males were obtained for doses as low as 25 Gy. Egg hatch was inhibited for irradiated males crossed with irradiated females at a low dose of 20 Gy. However, we estimated that to achieve 99.9% sterility (standard goal of many sterile insect technique programs), irradiation doses had to be increased to a dose between 50 and 75 Gy. At doses of 25 Gy and greater, we observed a decreasing trend in adult flight ability and an increasing trend in adult mortality. Such differences were greater for pupae irradiated at a young age compared those irradiated 24 h before emergence. Our single most relevant finding was that sterility induction (i.e., oviposition of nonfertilized eggs) was two times greater for males irradiated at low doses (40 Gy) than for males irradiated at high doses (80 Gy) when used at a 3:1:1 sterilized male to fertile male to fertile female ratio. Males irradiated at high doses may have been outcompeted by unirradiated males when courting unirradiated females. Implications of our findings for sterile insect technique programs are discussed.     

Pre-germination seed-phytochrome signals control stem extension in dark-grown Arabidopsis seedlings.

The developmental pattern of dark-grown Arabidopsis thaliana is dramatically shifted by exposure of the seedlings to light: inhibition of hypocotyl (stem) growth is one of the typical responses. Here, we show that the hypocotyl growth of dark-grown seedlings is reduced by exposure of the seeds to light. The light signal is perceived by phytochromes A and B during the hours immediately prior to seed germination. The effect is obviously selective, as other processes under phytochrome control were not equally affected by the pre-germination light cue. The hypocotyl response persists for two days after termination of the light signal, which is more than the persistence observed when the seedlings themselves receive the light stimulus. Treatment with far-red light, which converts phytochrome to the inactive form, did not reduce the hypocotyl growth response to pre-germination light, indicating that the persistent signal was not active phytochrome itself. We propose that trans-developmental phase signals could help plants to adjust to their environment.     

Fluorescence resonance energy transfer analysis of subunit stoichiometry of the epithelial Na+ channel

Activity of the epithelial Na(+) channel (ENaC) is rate-limiting for Na(+) (re)absorption across electrically tight epithelia. ENaC is a heteromeric channel comprised of three subunits, alpha, beta, and gamma, with each subunit contributing to the functional channel pore. The subunit stoichiometry of ENaC remains uncertain with electrophysiology and biochemical experiments supporting both a tetramer with a 2alpha:1beta:1gamma stoichiometry and a higher ordered channel with a 3alpha:3beta:3gamma stoichiometry. Here we used an independent biophysical approach based upon fluorescence resonance energy transfer (FRET) between differentially fluorophore-tagged ENaC subunits to determine the subunit composition of mouse ENaC functionally reconstituted in Chinese hamster ovary and COS-7 cells. We found that when all three subunits were co-expressed, ENaC contained at least two of each type of subunit. Findings showing that ENaC subunits interact with similar subunits in immunoprecipitation studies are consistent with these FRET results. Upon native polyacrylamide gel electrophoresis, moreover, oligomerized ENaC runs predominantly as a single species with a molecular mass of >600 kDa. Because single ENaC subunits have a molecular mass of approximately 90 kDa, these results also agree with the FRET results. The current results as a whole, thus, are most consistent with a higher ordered channel possibly with a 3alpha:3beta:3gamma stoichiometry.     

Factors determining tadpole vulnerability to predators: can prior experience compensate for a suboptimal shape?

We investigated the role of constitutive morphology and previous experience in predator avoidance in two anuran species associated with different larval habitats. In Rana temporaria, deeper tails and larger body size conferred selective advantage against dragonfly predation. Previous experience with predators had a positive influence on the survival of R. temporaria tadpoles equivalent to predator selection. By contrast, survival in Bufo bufo seems unrelated to tail shape or experience. This suggests that B. bufo lacks constitutive morphological defenses against insect predators, and that morphological and behavioral defenses could result more effective than chemical deterrents for these insect predators. A key novelty of this study is the observation that Rana tadpoles having prior experience with predators have an enhanced success in further encounters, and this occurs before the morphological induced defense has been established. This induced modification for R. temporaria, and its lack of for B. bufo, may be an important determinant of larval survival.     

A Calcium-Receptor Agonist Induces Gustatory Neural Responses in Bullfrogs

The effect of calcium-sensing receptor (CaR) agonists on frog gustatory responses was studied using glossopharyngeal nerve recording and whole-cell patch-clamp recording of isolated taste disc cells. Calcimimetic NPS R-467 dissolved in normal saline solution elicited a large transient response in the nerve. The less active enantiomer of the compound, NPS S-467 induced only a small neural response. The EC₅₀ for NPS R-467 was about 20 μM. Cross-adaptation experiments were performed to examine the effect of 30 μM NPS R-467 and 100 μM quinine on the gustatory neural response. The magnitude of the R-467-induced response after adaptation to quinine was approximately equal to that after adaptation to normal saline solution, indicating that the receptor site for NPS R-467 is different from the site for quinine. NPS R-467 (100 μM) also induced an inward current accompanied with conductance increase and large depolarization in two (13%) of 15 rod cells, and a sustained decrease in outward current and small depolarization in six (40%) other rod cells. NPS S-467 (100 μM) induced a sustained decrease in outward current and depolarization in five (50%) of 10 rod cells. Another calcimimetic cinacalcet (100 μM) induced an inward current accompanied with conductance increase in three (27%) of 11 rod cells. The results suggest that NPS R-467 induces neural responses through cell responses unrelated to a resting K⁺ conductance decrease.     

Life history and larval morphology of Eurhinus magnificus Gyllenhal (Coleoptera: Curculionidae), a new weevil to the United States

Eurhinus magnificus Gyllenhal has been collected in south Florida, presumably introduced through trade with countries in its native range. Very little information has been published on the biology or taxonomy of this insect. We conducted studies to investigate various aspects of its life history and host plant associations. The pre-imaginal life stages of E. magnificus are described for the first time. Dimensions of the adult, egg, larval, and pupal stages are also provided; head capsule measurement revealed five larval instars. All life stages of E. magnificus were collected at several sites in Broward and Miami-Dade counties from the host plant Cissus verticillata (L.) Nicolson & Jarvis (Vitaceae). Eggs were laid singly within the succulent, young subterminal portion of the host plant stem, one or two occurring between two nodes. Gall formation was apparent by the first to third instar and continued to increase in size until pupation which occurred within the gall. Predators and pathogens appeared to be responsible for considerable mortality in the field; there was no evidence of parasitism of any of the life stages. Greenhouse studies were undertaken to determine E. magnificus development time and host specificity. Adult weevils attacked grape cultivars (Vitis spp.) and feeding opened the stems to fungal agents but no physical evidence of larval development was apparent on grapes.     

Association of TLR4 polymorphisms with symptomatic respiratory syncytial virus infection in high-risk infants and young children

Respiratory syncytial virus (RSV) is a leading cause of infant mortality worldwide. Although anti-RSV Ab prophylaxis has greatly reduced infant mortality in the United States, there is currently no vaccine or effective antiviral therapy. RSV fusion (F) protein activates cells through TLR4. Two single nucleotide polymorphisms (SNPs) encoding Asp299Gly and Thr399Ile substitutions in the TLR4 ectodomain were previously associated with TLR4 hyporesponsiveness and increased susceptibility to bacterial infection. Prevalence of these SNPs was analyzed in a case series of 105 DNA samples extracted from archived nasal lavage samples from high-risk infants/young children with confirmed RSV disease who participated in two seminal clinical trials for anti-RSV prophylaxis. Frequencies of TLR4 SNPs in the case series were compared with those of literature controls, healthy adults, infants, and young children who presented with symptoms of respiratory infections (but not preselected for high risk for RSV). Both SNPs were highly associated with symptomatic RSV disease in this largely premature population (p < 0.0001), with 89.5% and 87.6% of cases being heterozygous for Asp299Gly and Thr399Ile polymorphisms versus published control frequencies of 10.5% and 6.5%, respectively. The other two control groups had similarly low frequencies. Our data suggest that heterozygosity of these two extracellular TLR4 polymorphisms is highly associated with symptomatic RSV disease in high-risk infants and support a dual role for TLR4 SNPs in prematurity and increased susceptibility to RSV not revealed by analysis of either alone.     

A bizarre Cretaceous theropod dinosaur from Patagonia and the evolution of Gondwanan dromaeosaurids

Fossils of a predatory dinosaur provide novel information about the evolution of unenlagiines, a poorly known group of dromaeosaurid theropods from Gondwana. The new dinosaur is the largest dromaeosaurid yet discovered in the Southern Hemisphere and depicts bizarre cranial and postcranial features. Its long and low snout bears numerous, small-sized conical teeth, a condition resembling spinosaurid theropods. Its short forearms depart from the characteristically long-armed condition of all dromaeosaurids and their close avian relatives. The new discovery amplifies the range of morphological disparity among unenlagiines, demonstrating that by the end of the Cretaceous this clade included large, short-armed forms alongside crow-sized, long-armed, possibly flying representatives. The new dinosaur is the youngest record of dromaeosaurids from Gondwana and represents a previously unrecognized lineage of large predators in Late Cretaceous dinosaur faunas mainly dominated by abelisaurid theropods.