Reflexes and preflexes: on the role of sensory feedback on rhythmic patterns in insect locomotion

Neuromuscular systems are stabilized and controlled by both feedforward and feedback signals. Feedforward pathways driven by central pattern generators (CPGs), in conjunction with preflexive mechanical reaction forces and nonlinear muscle properties, can produce stable stereotypical gaits. Feedback is nonetheless present in both slow and rapid running, and preflexive mechanisms can join with neural reflexes originating in proprioceptive sensors to yield robust behavior in uncertain environments. Here, we develop a single degree-of-freedom neuromechanical model representing a joint actuated by an agonist/antagonist muscle pair driven by motoneurons and a CPG in a periodic rhythm characteristic of locomotion. We consider two characteristic feedback modes: phasic and tonic. The former encodes states such as position in the timing of individual spikes, while the latter can transmit graded measures of force and other continuous variables as spike rates. We use results from phase reduction and averaging theory to predict phase relationships between CPG and motoneurons in the presence of feedback and compare them with simulations of the neuromechanical model, showing that both phasic and tonic feedback can shift motoneuronal timing and thereby affect joint motions. We find that phase changes in neural activation can cooperate with preflexive displacement and velocity effects on muscle force to compensate for externally applied forces, and that these effects qualitatively match experimental observations in the cockroach.     

Fusarium genomic resources: Tools to limit crop diseases and mycotoxin contamination

It has been almost 10 years since Joan Bennett suggested that fungal biologists create a “wish list” for fungal genome sequences (Bennett JW. White paper: Genomics for filamentous fungi. Fungal Genet Biol 1997; 21: 3–7). The availability of over 200 review papers concerning fungal genomics is a reflection of significant progress with a diversity of fungal species. Although much progress has been made, the use of genomic data to study mycotoxin synthesis and function, pathogenesis and other aspects of fungal biology is in its infancy. Here, we briefly present the status of publicly available genomic resources for Fusarium, a genus of important plant pathogenic and mycotoxin-producing fungi of worldwide concern. Preliminary examination of microarray data collected from F. verticillioides liquid cultures provides evidence of widespread differential gene expression over time.     

Phenotype microarray profiling of Staphylococcus aureus menD and hemB mutants with the small-colony-variant phenotype

Standard biochemical tests have revealed that hemin and menadione auxotrophic Staphylococcus aureus small-colony variants (SCVs) exhibit multiple phenotypic changes. To provide a more complete analysis of the SCV phenotype, two genetically defined mutants with a stable SCV phenotype were comprehensively tested. These mutants, generated via mutations in menD or hemB that yielded menadione and hemin auxotrophs, were subjected to phenotype microarray (PM) analysis of over 1,500 phenotypes (including utilization of different carbon, nitrogen, phosphate, and sulfur sources; growth stimulation or inhibition by amino acids and other nutrients, osmolytes, and metabolic inhibitors; and susceptibility to antibiotics). Compared to parent strain COL, the hemB mutant was defective in utilization of a variety of carbon sources, including Krebs cycle intermediates and compounds that ultimately generate ATP via electron transport. The phenotype of the menD mutant was similar to that of the hemB mutant, but the defects in carbon metabolism were more pronounced than those seen with the hemB mutant. In both mutant strains, hexose phosphates and other carbohydrates that provide ATP in the absence of electron transport stimulated growth. Other phenotypes of SCV mutants, such as hypersensitivity to sodium selenite, sodium tellurite, and sodium nitrite, were also uncovered by the PM analysis. Key results of the PM analysis were confirmed in independent growth studies and by using Etest strips for susceptibility testing. PM technology is a new and efficient technology for assessing cellular phenotypes in S. aureus.     

Syntaxin 16 controls the intracellular sequestration of GLUT4 in 3T3-L1 adipocytes

The regulated delivery of Glut4-containing vesicles to the plasma membrane is a specialised example of regulated membrane trafficking. Present models favour the transporter trafficking through two inter-related endosomal cycles. The first is the proto-typical endosomal system. This is a fast trafficking event that, in the absence of insulin, serves to internalise Glut4 from the plasma membrane. Once in this pathway, Glut4 is further sorted into a slowly recycling pathway that operates between recycling endosomes, the trans Golgi network, and a population of vesicles often referred to as Glut4-storage vesicles. Little is known about the molecules that regulate these distinct sorting steps. Here, we have studied the role of Stx16 in Glut4 trafficking. Using two independent strategies, we show that Stx16 plays a crucial role in Glut4 traffic in 3T3-L1 adipocytes. Over-expression of a mutant form of Stx16 devoid of a transmembrane anchor was found to significantly slow the reversal of insulin-stimulated glucose transport. Depletion of Stx16 using antisense approaches profoundly reduced insulin-stimulated glucose transport but was without effect on cell surface transferrin receptor levels, and also reduced the extent of Glut4 translocation to the plasma membrane in response to insulin. These data support a model in which Stx16 is crucial in the sorting of Glut4 from the fast cycling to the slow cycling intracellular trafficking pathways in adipocytes.     

Contributions of turgor pressure, the contractile ring, and septum assembly to forces in cytokinesis in fission yeast

A paradigm of cytokinesis in animal cells is that the actomyosin contractile ring provides the primary force to divide the cell [1]. In the fission yeast Schizosaccharomyces pombe, cytokinesis also involves a conserved cytokinetic ring, which has been generally assumed to provide the force for cleavage [2-4] (see also [5]). However, in contrast to animal cells, cytokinesis in yeast cells also requires the assembly of a cell wall septum [6], which grows centripetally inward as the ring closes. Fission yeast, like other walled cells, also possess high (MPa) turgor pressure [7-9]. Here, we show that turgor pressure is an important factor in the mechanics of cytokinesis. Decreasing effective turgor pressure leads to an increase in cleavage rate, suggesting that the inward force generated by the division apparatus opposes turgor pressure. The contractile ring, which is predicted to provide only a tiny fraction of the mechanical stress required to overcome turgor, is largely dispensable for ingression; once septation has started, cleavage can continue in the absence of the contractile ring. Scaling arguments and modeling suggest that the large forces for cytokinesis are not produced by the contractile ring but are driven by the assembly of cell wall polymers in the growing septum.     

Feeding history and obese-prone genotype increase survival of rats exposed to a challenge of food restriction and wheel running

We hypothesized that obese-prone genotype and history of food restriction confer a survival advantage to genetically obese animals under environmental challenge. Male juvenile JCR:LA-cp rats, obese-prone and lean-prone, were exposed to 1.5 h daily meals and 22.5-h voluntary wheel running, a procedure inducing activity anorexia (AA). One week before the AA challenge, obese-prone rats were freely fed (obese-FF), or pair fed (obese-PF) to lean-prone, free-feeding rats (lean-FF). Animals were removed from protocol at 75% of initial body weight (starvation criterion) or after 14 days (survival criterion). AA challenge induced weight loss in all rats, but percent weight loss was more rapid and sustained in lean-FF rats than in obese-FF or obese-PF animals (P < 0.04). Weight loss was significantly higher in obese-FF rats than obese-PF rats, 62% of which achieved survival criterion and stabilized with zero weight loss. Obese-PF rats survived longer, on average (12.0 ± 1.1 day) than obese-FF (8.2 ± 1.1 day) and lean-FF rats (3.5 ± 0.2 day) (P < 0.02). Wheel running increased linearly in all groups; lean-FF increased more rapidly than obese-FF (P < 0.05); obese-PF increased at an intermediate rate (P < 0.02), and those rats that survived stabilized daily rates of wheel running. Prior food restriction of juvenile obese-prone rats induces a survival benefit beyond genotype, that is related to achievement of homeostasis. This metabolic adaptive process may help explain the development of human obesity in the presence of an unstable food environment which subsequently transitions to an abundant food supply.     

Molecular Imaging Reveals a Progressive Pulmonary Inflammation in Lower Airways in Ferrets Infected with 2009 H1N1 Pandemic Influenza Virus

Molecular imaging has gained attention as a possible approach for the study of the progression of inflammation and disease dynamics. Herein we used [¹⁸F]-2-deoxy-2-fluoro-D-glucose ([¹⁸F]-FDG) as a radiotracer for PET imaging coupled with CT (FDG-PET/CT) to gain insight into the spatiotemporal progression of the inflammatory response of ferrets infected with a clinical isolate of a pandemic influenza virus, H1N1 (H1N1pdm). The thoracic regions of mock- and H1N1pdm-infected ferrets were imaged prior to infection and at 1, 2, 3 and 6 days post-infection (DPI). On 1 DPI, FDG-PET/CT imaging revealed areas of consolidation in the right caudal lobe which corresponded with elevated [¹⁸F]-FDG uptake (maximum standardized uptake values (SUVMax), 4.7–7.0). By days 2 and 3, consolidation (CT) and inflammation ([¹⁸F]-FDG) appeared in the left caudal lobe. By 6 DPI, CT images showed extensive areas of patchy ground-glass opacities (GGO) and consolidations with the largest lesions having high SUVMax (6.0–7.6). Viral shedding and replication were detected in most nasal, throat and rectal swabs and nasal turbinates and lungs on 1, 2 and 3 DPI, but not on day 7, respectively. In conclusion, molecular imaging of infected ferrets revealed a progressive consolidation on CT with corresponding [¹⁸F]-FDG uptake. Strong positive correlations were measured between SUVMax and bronchiolitis-related pathologic scoring (Spearman’s ρ = 0.75). Importantly, the extensive areas of patchy GGO and consolidation seen on CT in the ferret model at 6 DPI are similar to that reported for human H1N1pdm infections. In summary, these first molecular imaging studies of lower respiratory infection with H1N1pdm show that FDG-PET can give insight into the spatiotemporal progression of the inflammation in real-time.     

A genome-wide scan of Ashkenazi Jewish Crohn's disease suggests novel susceptibility loci

Crohn''s disease (CD) is a complex disorder resulting from the interaction of intestinal microbiota with the host immune system in genetically susceptible individuals. The largest meta-analysis of genome-wide association to date identified 71 CD–susceptibility loci in individuals of European ancestry. An important epidemiological feature of CD is that it is 2–4 times more prevalent among individuals of Ashkenazi Jewish (AJ) descent compared to non-Jewish Europeans (NJ). To explore genetic variation associated with CD in AJs, we conducted a genome-wide association study (GWAS) by combining raw genotype data across 10 AJ cohorts consisting of 907 cases and 2,345 controls in the discovery stage, followed up by a replication study in 971 cases and 2,124 controls. We confirmed genome-wide significant associations of 9 known CD loci in AJs and replicated 3 additional loci with strong signal (p<5×10⁻⁶). Novel signals detected among AJs were mapped to chromosomes 5q21.1 (rs7705924, combined p = 2×10⁻⁸; combined odds ratio OR = 1.48), 2p15 (rs6545946, p = 7×10⁻⁹; OR = 1.16), 8q21.11 (rs12677663, p = 2×10⁻⁸; OR = 1.15), 10q26.3 (rs10734105, p = 3×10⁻⁸; OR = 1.27), and 11q12.1 (rs11229030, p = 8×10⁻⁹; OR = 1.15), implicating biologically plausible candidate genes, including RPL7, CPAMD8, PRG2, and PRG3. In all, the 16 replicated and newly discovered loci, in addition to the three coding NOD2 variants, accounted for 11.2% of the total genetic variance for CD risk in the AJ population. This study demonstrates the complementary value of genetic studies in the Ashkenazim.     

Sex-specific influence of aging on exercising leg blood flow.

Our previous work suggests that healthy human aging is associated with sex-specific differences in leg vascular responses during large muscle mass exercise (2-legged cycling) (Proctor DN, Parker BA. Microcirculation 13: 315-327, 2006). The present study determined whether age x sex interactions in exercising leg hemodynamics persist during small muscle mass exercise that is not limited by cardiac output. Thirty-one young (20-30 yr; 15 men/16 women) and 31 older (60-79 yr; 13 men/18 women) healthy, normally active adults performed graded single-leg knee extensions to maximal exertion. Femoral artery blood velocity and diameter (Doppler ultrasound), heart rate (ECG), and beat-to-beat arterial blood pressure (mean arterial pressure, radial artery tonometry) were measured during each 3-min work rate (4.8 and 8 W/stage for women and men, respectively). The results (means +/- SE) were as follows. Despite reduced resting leg blood flow and vascular conductance, older men exhibited relatively preserved exercising leg hemodynamic responses. Older women, by contrast, exhibited attenuated hyperemic (young: 52 +/- 3 ml.min(-1).W(-1); vs. older: 40 +/- 4 ml.min(-1).W(-1); P = 0.02) and vasodilatory responses (young: 0.56 +/- 0.06 ml.min(-1).mmHg(-1).W(-1) vs. older: 0.37 +/- 0.04 ml.min(-1).mmHg(-1) W(-1); P < 0.01) to exercise compared with young women. Relative (percentage of maximal) work rate comparisons of all groups combined also revealed attenuated vasodilator responses in older women (P < 0.01 for age x sex x work rate interaction). These sex-specific age differences were not abolished by consideration of hemoglobin, quadriceps muscle, muscle recruitment, and mechanical influences on muscle perfusion. Collectively, these findings suggest that local factors contribute to the sex-specific effects of aging on exercising leg hemodynamics in healthy adults.