Dynamics and stability of legged locomotion in the horizontal plane: a test case using insects

 Motivated by experimental studies of insects, we propose a model for legged locomotion in the horizontal plane. A three-degree-of freedom, energetically conservative, rigid-body model with a pair of compliant virtual legs in intermittent contact with the ground allows us to study how dynamics depends on parameters such as mass, moment of inertia, leg stiffness, and length. We find periodic gaits, and show that mechanics alone can confer asymptotic stability of relative heading and body angular velocity. We discuss the relevance of our idealized models to experiments and simulations on insect running, showing that their gait and force characteristics match observations reasonably well. We perform parameter studies and suggest that our model is relevant to the understanding of locomotion dynamics across species. Received: 17 April 2001 / Accepted in revised form: 20 November 2001     

Regulation of mitochondrial glutathione redox status and protein glutathionylation by respiratory substrates

Brain and liver mitochondria isolated by a discontinuous Percoll gradient show an oxidized redox environment, which is reflected by low GSH levels and high GSSG levels and significant glutathionylation of mitochondrial proteins as well as by low NAD(P)H/NAD(P) values. The redox potential of brain mitochondria isolated by a discontinuous Percoll gradient method was calculated to be -171 mV based on GSH and GSSG concentrations. Immunoblotting and LC/MS/MS analysis revealed that succinyl-CoA transferase and ATP synthase (F(1) complex, α-subunit) were extensively glutathionylated; S-glutathionylation of these proteins resulted in a substantial decrease of activity. Supplementation of mitochondria with complex I or complex II respiratory substrates (malate/glutamate or succinate, respectively) increased NADH and NADPH levels, resulting in the restoration of GSH levels through reduction of GSSG and deglutathionylation of mitochondrial proteins. Under these conditions, the redox potential of brain mitochondria was calculated to be -291 mV. Supplementation of mitochondria with respiratory substrates prevented GSSG formation and, consequently, ATP synthase glutathionylation in response to H(2)O(2) challenges. ATP synthase appears to be the major mitochondrial protein that becomes glutathionylated under oxidative stress conditions. Glutathionylation of mitochondrial proteins is a major consequence of oxidative stress, and respiratory substrates are key regulators of mitochondrial redox status (as reflected by thiol/disulfide exchange) by maintaining mitochondrial NADPH levels.     

Effect of Docosahexaenoic Acid on the Synthesis of Phosphatidylserine in Rat Brain Microsomes and C6 Glioma Cells

Abstract: Docosahexaenoic acid (22:6n-3) is the major polyunsaturated fatty acid (PUFA) in the CNS and accumulates particularly in phosphatidylserine (PS). We have investigated the effect of the 22:6n-3 compositional status on the synthesis of PS. The fatty acid composition of brain microsomes from offspring of rats artificially reared on an n-3-deficient diet showed a dramatic reduction of 22:6n-3 content (1.7 ± 0.1%) when compared with control animals (15.0 ± 0.2%). The decrease was accompanied by an increase in docosapentaenoic acid (22:5n-6) content, which replaced the 22:6n-3 phospholipids with 22:5n-6 molecular species, as demonstrated using HPLC/electrospray mass spectrometry. The n-3 deficiency did not affect the total amount of polyunsaturated phospholipids in brain microsomes; however, it was associated with a decrease in the total polyunsaturated PS content and with increased levels of 1-stearoyl-2-docosapentanoyl (18:0/22:5n-6) species, particularly in phosphatidylcholine. Incorporation of [³H]serine into PS in rat brain microsomes from n-3-deficient animals was slightly but significantly less than that of the control animals. Similarly, C6 glioma cells cultured for 24 h in 22:6n-3-supplemented media (10–40 µ M ) showed a significant increase in the synthesis of [³H]PS when compared with unsupplemented cells. Our data show that neuronal and glial PS synthesis is sensitive to changes in the docosahexaenoate levels of phospholipids and suggest that 22:6n-3 may be a modulator of PS synthesis.     

<Emphasis Type="Italic">Malassezia</Emphasis> spp. in Acoustic Meatus of Bats (<Emphasis Type="Italic">Molossus molossus</Emphasis>) of the Amazon Region,Brazil

The yeasts of the Malassezia genus are opportunistic microorganisms and can cause human and animal infections. They are commonly isolated from the skin and auricular canal of mammalians, mainly dogs and cats. The present study was aimed to isolate Malassezia spp. from the acoustic meatus of bats (Molossus molossus) in the Montenegro region, “Rondônia”, Brazil. From a total of 30 bats studied Malassezia spp. were isolated in 24 (80%) animals, the breakdown by species being as follows (one Malassezia sp. per bat, N = 24): 15 (62.5%) M. pachydermatis, 5 (20.8%) M. furfur, 3 (12.5%) M. globosa and 1 (4.2%) M. sympodialis. This study establishes a new host and anatomic place for Malassezia spp., as it presents the first report ever of the isolation of this genus of yeasts in the acoustic meatus of bats.     

Constitutively Active Mitogen-Activated Protein Kinase Versions Reveal Functions of Arabidopsis MPK4 in Pathogen Defense Signaling

Plant mitogen-activated protein kinases (MAPKs) are involved in important processes, including stress signaling and development. In a functional yeast screen, we identified mutations that render Arabidopsis thaliana MAPKs constitutively active (CA). Importantly, CA-MAPKs maintain their specificity toward known activators and substrates. As a proof-of-concept, Arabidopsis MAPK4 (MPK4) function in plant immunity was investigated. In agreement with the phenotype of mpk4 mutants, CA-MPK4 plants were compromised in pathogen-induced salicylic acid accumulation and disease resistance. MPK4 activity was found to negatively regulate pathogen-associated molecular pattern-induced reactive oxygen species production but had no impact on callose deposition, indicating that CA-MPK4 allows discriminating between processes regulated by MPK4 activity from processes indirectly affected by mpk4 mutation. Finally, MPK4 activity was also found to compromise effector-triggered immunity conditioned by the Toll Interleukin-1 Receptor–nucleotide binding (NB)–Leu-rich repeat (LRR) receptors RPS4 and RPP4 but not by the coiled coil–NB-LRR receptors RPM1 and RPS2. Overall, these data reveal important insights on how MPK4 regulates plant defenses and establishes that CA-MAPKs offer a powerful tool to analyze the function of plant MAPK pathways.     

A Comparative Study of Peripheral Immune Responses to Taenia solium in Individuals with Parenchymal and Subarachnoid Neurocysticercosis

Background

The ability of Taenia solium to modulate the immune system likely contributes to their longevity in the human host. We tested the hypothesis that the nature of the immune response is related to the location of parasite and clinical manifestations of infection.

Methodology

Peripheral blood mononuclear cells (PBMC) were obtained from untreated patients with neurocysticercosis (NCC), categorized as having parenchymal or subarachnoid infection by the presence of cysts exclusively within the parenchyma or in subarachnoid spaces of the brain, and from uninfected (control) individuals matched by age and gender to each patient. Using multiplex detection technology, sera from NCC patients and controls and cytokine production by PBMC after T. solium antigen (TsAg) stimulation were assayed for levels of inflammatory and regulatory cytokines. PBMC were phenotyped by flow cytometry ex vivo and following in vitro stimulation with TsAg.

Principal Findings

Sera from patients with parenchymal NCC demonstrated significantly higher Th1 (IFN-γ/IL-12) and Th2 (IL-4/IL-13) cytokine responses and trends towards higher levels of IL-1β/IL-8/IL-5 than those obtained from patients with subarachnoid NCC. Also higher in vitro antigen-driven TNF-β secretion was detected in PBMC supernatants from parenchymal than in subarachnoid NCC. In contrast, there was a significantly higher IL-10 response to TsAg stimulation in patients with subarachnoid NCC compared to parenchymal NCC. Although no differences in regulatory T cells (Tregs) frequencies were found ex vivo, there was a trend towards greater expansion of Tregs upon TsAg stimulation in subarachnoid than in parenchymal NCC when data were normalized for the corresponding controls.

Conclusions/Significance

T. solium infection of the subarachnoid space is associated with an enhanced regulatory immune response compared to infection in the parenchyma. The resulting anti-inflammatory milieu may represent a parasite strategy to maintain a permissive environment in the host or diminish inflammatory damage from the host immune response in the central nervous system.     

Differential response to frameshift signals in eukaryotic and prokaryotic translational systems.

The genomic RNA of beet western yellows virus (BWYV) contains a potential translational frameshift signal in the overlap region of open reading frames ORF2 and ORF3. The signal, composed of a heptanucleotide slippery sequence and a downstream pseudoknot, is similar in appearance to those identified in retroviral RNAs. We have examined whether the proposed BWYV signal functions in frameshifting in three translational systems, i.c. in vitro in a reticulocyte lysate or a wheat germ extract and in vivo in E. coli. The efficiency of the signal in the eukaryotic system is low but significant, as it responds strongly to changes in either the slip sequence or the pseudoknot. In contrast, in E. coli there is hardly any response to the same changes. Replacing the slip sequence to the typical prokaryotic signal AAAAAAG yields more than 5% frameshift in E. coli. In this organism the frameshifting is highly sensitive to changes in the slip sequence but only slightly to disruption of the pseudoknot. The eukaryotic assay systems are barely sensitive to changes in either AAAAAAG or in the pseudoknot structure in this construct. We conclude that eukaryotic frameshift signals are not recognized by prokaryotes. On the other hand the typical prokaryotic slip sequence AAAAAAG does not lead to significant frameshifting in the eukaryote. In contrast to recent reports on the closely related potato leafroll virus (PLRV) we show that the frameshifting in BWYV is pseudoknot-dependent.     

Melatonin reduces rat hepatic macromolecular damage due to oxidative stress caused by delta-aminolevulinic acid

Delta-aminolevulinic acid, precursor of heme, accumulates in a number of organs, especially in the liver, of patients with acute intermittent porphyria. The potential protective effect of melatonin against oxidative damage to nuclear DNA and microsomal and mitochondrial membranes in rat liver, caused by delta-aminolevulinic acid, was examined. Changes in 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels, an index of DNA damage, and alterations in membrane fluidity (the inverse of membrane rigidity) and lipid peroxidation in microsomal and mitochondrial membranes, as indices of damage to lipid and protein molecules in membranes, were estimated. Measurements were made in rat liver after a 2 week treatment with delta-aminolevulinic acid (40 mg/kg b.w., every other day). To test the potential protective effects of melatonin, the indole was injected (i.p. 10 mg/kg b.w.) 3 times daily for 2 weeks. 8-OHdG levels and lipid peroxidation in microsomal membranes increased significantly whereas microsomal and mitochondrial membrane fluidity decreased as a consequence of delta-aminolevulinic acid treatment. Melatonin completely counteracted the effects of delta-aminolevulinic acid. Melatonin was highly effective in protecting against oxidative damage to DNA as well as to microsomal and mitochondrial membranes in rat liver and it may be useful as a cotreatment in patients with acute intermittent porphyria.     

Modifications of human histone H3 variants during mitosis

Phosphorylation of histone H3 is a hallmark event in mitosis and is associated with chromosome condensation. Here, we use a combination of immobilized metal affinity chromatography and tandem mass spectrometry to characterize post-translational modifications associated with phosphorylation on the N-terminal tails of histone H3 variants purified from mitotically arrested HeLa cells. Modifications observed in vivo on lysine residues adjacent to phosphorylated Ser and Thr provide support for the existence of the "methyl/phos", binary-switch hypothesis [Fischle, W., Wang, Y., and Allis, C. D. (2003) Nature 425, 475-479]. ELISA with antibodies selective for H3 at Ser10, Ser28, and Thr3 show reduced activity when adjacent Lys residues are modified. When used together, mass spectrometry and immunoassay methods provide a powerful approach for elucidation of the histone code and identification of histone post-translational modifications that occur during mitosis and other specific cellular events.     

Bayesian mapping of multiple traits in maize: the importance of pleiotropic effects in studying the inheritance of quantitative traits

Pleiotropy has played an important role in understanding quantitative traits. However, the extensiveness of this effect in the genome and its consequences for plant improvement have not been fully elucidated. The aim of this study was to identify pleiotropic quantitative trait loci (QTLs) in maize using Bayesian multiple interval mapping. Additionally, we sought to obtain a better understanding of the inheritance, extent and distribution of pleiotropic effects of several components in maize production. The design III procedure was used from a population derived from the cross of the inbred lines L-14-04B and L-08-05F. Two hundred and fifty plants were genotyped with 177 microsatellite markers and backcrossed to both parents giving rise to 500 backcrossed progenies, which were evaluated in six environments for grain yield and its components. The results of this study suggest that mapping isolated traits limits our understanding of the genetic architecture of quantitative traits. This architecture can be better understood by using pleiotropic networks that facilitate the visualization of the complexity of quantitative inheritance, and this characterization will help to develop new selection strategies. It was also possible to confront the idea that it is feasible to identify QTLs for complex traits such as grain yield, as pleiotropy acts prominently on its subtraits and as this "trait" can be broken down and predicted almost completely by the QTLs of its components. Additionally, pleiotropic QTLs do not necessarily signify pleiotropy of allelic interactions, and this indicates that the pervasive pleiotropy does not limit the genetic adaptability of plants.