Models of Postural Control: Shared Variance in Joint and COM Motions

This paper investigated the organization of the postural control system in human upright stance. To this aim the shared variance between joint and 3D total body center of mass (COM) motions was analyzed using multivariate canonical correlation analysis (CCA). The CCA was performed as a function of established models of postural control that varied in their joint degrees of freedom (DOF), namely, an inverted pendulum ankle model (2DOF), ankle-hip model (4DOF), ankle-knee-hip model (5DOF), and ankle-knee-hip-neck model (7DOF). Healthy young adults performed various postural tasks (two-leg and one-leg quiet stances, voluntary AP and ML sway) on a foam and rigid surface of support. Based on CCA model selection procedures, the amount of shared variance between joint and 3D COM motions and the cross-loading patterns we provide direct evidence of the contribution of multi-DOF postural control mechanisms to human balance. The direct model fitting of CCA showed that incrementing the DOFs in the model through to 7DOF was associated with progressively enhanced shared variance with COM motion. In the 7DOF model, the first canonical function revealed more active involvement of all joints during more challenging one leg stances and dynamic posture tasks. Furthermore, the shared variance was enhanced during the dynamic posture conditions, consistent with a reduction of dimension. This set of outcomes shows directly the degeneracy of multivariate joint regulation in postural control that is influenced by stance and surface of support conditions.     

Plastid stromules are induced by stress treatments acting through abscisic acid

Stromules are highly dynamic stroma-filled tubules that extend from the surface of all plastid types in all multi-cellular plants examined to date. The stromule frequency (percentage of plastids with stromules) has generally been regarded as characteristic of the cell and tissue type. However, the present study shows that various stress treatments, including drought and salt stress, are able to induce stromule formation in the epidermal cells of tobacco hypocotyls and the root hairs of wheat seedlings. Application of abscisic acid (ABA) to tobacco and wheat seedlings induced stromule formation very effectively, and application of abamine, a specific inhibitor of ABA synthesis, prevented stromule induction by mannitol. Stromule induction by ABA was dependent on cytosolic protein synthesis, but not plastid protein synthesis. Stromules were more abundant in dark-grown seedlings than in light-grown seedlings, and the stromule frequency was increased by transfer of light-grown seedlings to the dark and decreased by illumination of dark-grown seedlings. Stromule formation was sensitive to red and far-red light, but not to blue light. Stromules were induced by treatment with ACC (1-aminocyclopropane-1-carboxylic acid), the first committed ethylene precursor, and by treatment with methyl jasmonate, but disappeared upon treatment of seedlings with salicylate. These observations indicate that abiotic, and most probably biotic, stresses are able to induce the formation of stromules in tobacco and wheat seedlings.     

Adjusting HIV Prevalence for Survey Non-Response Using Mortality Rates: An Application of the Method Using Surveillance Data from Rural South Africa

Background

The main source of HIV prevalence estimates are household and population-based surveys; however, high refusal rates may hinder the interpretation of such estimates. The study objective was to evaluate whether population HIV prevalence estimates can be adjusted for survey non-response using mortality rates.

Methodology/Principal Findings

Data come from the longitudinal Africa Centre Demographic Information System (ACDIS), in rural South Africa. Mortality rates for persons tested and not tested in the 2005 HIV surveillance were available from routine household surveillance. Assuming HIV status among individuals contacted but who refused to test (non-response) is missing at random and mortality among non-testers can be related to mortality of those tested a mathematical model was developed. Non-parametric bootstrapping was used to estimate the 95% confidence intervals around the estimates. Mortality rates were higher among untested (16.9 per thousand person-years) than tested population (11.6 per thousand person-years), suggesting higher HIV prevalence in the former. Adjusted HIV prevalence for females (15–49 years) was 31.6% (95% CI 26.1–37.1) compared to observed 25.2% (95% CI 24.0–26.4). For males (15–49 years) adjusted HIV prevalence was 19.8% (95% CI 14.8–24.8), compared to observed 13.2% (95% CI 12.1–14.3). For both sexes (15–49 years) combined, adjusted prevalence was 27.5% (95% CI 23.6–31.3), and observed prevalence was 19.7% (95% CI 19.6–21.3). Overall, observed prevalence underestimates the adjusted prevalence by around 7 percentage points (37% relative difference).

Conclusions/Significance

We developed a simple approach to adjust HIV prevalence estimates for survey non-response. The approach has three features that make it easy to implement and effective in adjusting for selection bias than other approaches. Further research is needed to assess this approach in populations with widely available HIV treatment (ART).     

Seasonal utilization of different seston carbon sources by the ribbed mussel, Geukensia demissa (Dillwyn) in a mid-Atlantic salt marsh

Seston in salt marshes contains a temporally and spatially complex mixture of natural microparticulate organic material, including phytoplankton, vascular plant detritus, bacteria, heterotrophic nanoflagellates and benthic diatoms. Quantitative information is available concerning how suspension-feeding consumers, such as the ribbed mussel, Geukensia demissa (Dillwyn), utilize some of these components to satisfy their carbon demands. Despite this information there is still a limited understanding of how the relative nutritive contribution of these different dietary items may shift during the year associated with variations in both seston composition and the mussel's physiological condition. To investigate if the mussel's ability to use specific constituents of natural seston varies seasonally, we ran a series of pulse-chase 14C feeding experiments under ambient conditions in March, May, August and November 1996. Phytoplankton, cellulosic detritus, bacteria, heterotrophic nanoflagellates and benthic diatoms were radiolabeled and supplemented in small amounts to natural marsh water for feeding to mussels. The fate of 14C in mussel tissues, feces, respiration and excretion was quantified and contrasted among the different diet types and seasons. Microcapsules containing radiolabeled carbohydrate and protein were used as standards to differentiate possible between-experiment variations in seston composition from seasonal changes in the mussel's feeding and digestive physiology. Mussel clearance rates for all diets were highest in summer and autumn and lowest in winter and spring. In contrast, seasonal shifts in digestive physiology were only found for certain diets. The seasonal range of assimilation efficiencies for microcapsule standards (18-29%) and field-collected microheterotrophs (bacteria 76-93% and heterotrophic nanoflagellates 87-94%) did not differ significantly during the year, whereas summer and autumn assimilation efficiencies for cellulosic detritus (22-24%), phytoplankton (71-79%) and benthic diatoms (89-93%) were up to twofold greater than those in winter and spring (13%, 40-59% and 45-81%, respectively). We conclude that the digestive physiology (e.g., digestive enzyme production) of mussels responds to shifts in dietary components during the year.     

Is object search mediated by object-based or image-based representations?

Recent research suggests that visually specific memory representations for previously fixated objects are maintained during scene perception. Here we investigate the degree of visual specificity by asking whether the memory representations are image-based or object-based. To that end we measured the effects of object orientation on the time to search for a familiar object from amongst a set of 7 familiar distractors arranged in a circular array. Search times were found to depend on the relative orientations of the target object and the probe object for both familiar and novel objects. This effect was found to be partly an image matching effect but there was also an advantage shown for the object's canonical view for familiar objects. Orientation effects were maintained even when the target object was specified as having unique or similar shape properties relative to the distractors. Participants' eye movements were monitored during two of the experiments. Eye movement patterns revealed selection for object shape and object orientation during the search process. Our findings provide evidence for object representations during search that are detailed and share image-based characteristics with more high-level characteristics from object memory.     

BMPs signal alternately through a SMAD or FRAP-STAT pathway to regulate fate choice in CNS stem cells

The ability of stem cells to generate distinct fates is critical for the generation of cellular diversity during development. Central nervous system (CNS) stem cells respond to bone morphogenetic protein (BMP) 4 by differentiating into a wide variety of dorsal CNS and neural crest cell types. We show that distinct mechanisms are responsible for the generation of two of these cell types, smooth muscle and glia. Smooth muscle differentiation requires BMP-mediated Smad1/5/8 activation and predominates where local cell density is low. In contrast, glial differentiation predominates at high local densities in response to BMP4 and is specifically blocked by a dominant-negative mutant Stat3. Upon BMP4 treatment, the serine-threonine kinase FKBP12/rapamycin-associated protein (FRAP), mammalian target of rapamycin (mTOR), associates with Stat3 and facilitates STAT activation. Inhibition of FRAP prevents STAT activation and glial differentiation. Thus, glial differentiation by BMP4 occurs by a novel pathway mediated by FRAP and STAT proteins. These results suggest that a single ligand can regulate cell fate by activating distinct cytoplasmic signals.     

The ability of Fla-typing schemes to discriminate between strains of Campylobacter jejuni

AIMS: The aim of this investigation was to compare the usefulness of two previously published flagellin PCR-RFLP typing (Fla-typing) techniques for the subtyping of Campylobacter jejuni strains, in terms of ease of use and discriminatory power. METHODS AND RESULTS: Six groups of isolates, which were epidemiologically unrelated but with similar Fla-types, and five groups of epidemiologically related poultry isolates, with similar PFGE profiles, were used in the comparison. The Fla-typing methods used varied in the number and length of fla-genes amplified and the restriction enzymes used. In addition, the use of separately amplified PCR fragments of both the flaA and flaB genes to generate RFLP profiles was investigated. CONCLUSION: The results clearly demonstrated that both previously published methods exhibit some advantages over the other. However, optimal discrimination was obtained by the use of separately amplified PCR fragments of both fla-genes. SIGNIFICANCE AND IMPACT OF THE STUDY: The subtyping of Camp. jejuni isolates is considered essential for epidemiological purposes. Genotyping methods are now more frequently used but have yet to be standardized. Fla-typing is a rapid and easy to use method with acceptable discriminatory power. However, the discriminatory power of the currently published Fla-typing techniques may be further improved by incorporating RFLP profiles of both fla-genes.     

Cell surface targeting and clustering interactions between heterologously expressed PSD-95 and the Shal voltage-gated potassium channel, Kv4.2

Kv4.2 is a voltage-gated potassium channel that is critical in controlling the excitability of myocytes and neurons. Processes that influence trafficking and surface distribution patterns of Kv4.2 will affect its ability to contribute to cellular functions. The scaffolding/clustering protein PSD-95 regulates trafficking and distribution of several receptors and Shaker family Kv channels. We therefore investigated whether the C-terminal valine-serine-alanine-leucine (VSAL) of Kv4.2 is a novel binding motif for PSD-95. By using co-immunoprecipitation assays, we determined that full-length Kv4.2 and PSD-95 interact when co-expressed in mammalian cell lines. Mutation analysis in this heterologous expression system showed that the VSAL motif of Kv4.2 is necessary for PSD-95 binding. PSD-95 increased the surface expression of Kv4.2 protein and caused it to cluster, as shown by deconvolution microscopy and biotinylation assays. Deleting the C-terminal VSAL motif of Kv4.2 eliminated these effects, as did substituting a palmitoylation-deficient PSD-95 mutant. In addition to these effects of PSD-95 on Kv4.2 distribution, the channel itself promoted redistribution of PSD-95 to the cell surface in the heterologous expression system. This work represents the first evidence that a member of the Shal subfamily of Kv channels can bind to PSD-95, with functional consequences.