Biomechanics of conidial dispersal in the toxic mold Stachybotrys chartarum

Conidial dispersal in Stachybotrys chartarum in response to low-velocity airflow was studied using a microflow apparatus. The maximum rate of spore release occurred during the first 5 min of airflow, followed by a dramatic reduction in dispersal that left more than 99% of the conidia attached to their conidiophores. Micromanipulation of undisturbed colonies showed that micronewton (microN) forces were needed to dislodge spore clusters from their supporting conidiophores. Calculations show that airspeeds that normally prevail in the indoor environment disturb colonies with forces that are 1000-fold lower, in the nanonewton (nN) range. Low-velocity airflow does not, therefore, cause sufficient disturbance to disperse a large proportion of the conidia of S. chartarum.     

Endothelium-dependent and -independent relaxation in the forelimb and hindlimb vasculatures of swine

Limb differences in endothelial function exist between arm and leg vasculatures of humans. The current investigation tested the hypothesis that forelimb and hindlimb vasorelaxation are similar in the absence of limb differences in blood pressure. Conduit arteries (brachials/femorals) and second order arterioles were harvested from 22 miniature Yucatan swine. In vitro assessment of vasorelaxation was determined by administering increasing doses of bradykinin (BK), acetylcholine (ACh), and sodium nitroprusside (SNP). The role of the nitric oxide synthase (NOS) and cyclooxygenase (COX) pathways was assessed in conduit arteries but not resistance arterioles through L-NAME (300 microM) and INDO (5 microM) incubation, respectively. The relaxation responses to BK and ACh were similar in brachial and femoral arteries. SNP relaxation response was greater in the brachial compared to femoral arteries. There were also no significant differences in the relaxation responses of second order arterioles of the forelimb and hindlimb to BK, ACh, and SNP. Incubation of conduit arterial rings in L-NAME produced a greater reduction in BK and ACh relaxation in the brachial (approximately 25%) compared to femoral (approximately 13%) arterial rings. The current results of this investigation suggest that the forelimb and hindlimb vasculatures of swine have relatively similar vasorelaxation responses to both endothelium-dependent and -independent vasodilators.     

A role for Caenorhabditis elegans chromatin-associated protein HIM-17 in the proliferation vs. meiotic entry decision

Chromatin-associated protein HIM-17 was previously shown to function in the chromosomal events of meiotic prophase. Here we report an additional role for HIM-17 in regulating the balance between germ cell proliferation and meiotic development. A cryptic function for HIM-17 in promoting meiotic entry and/or inhibiting proliferation was revealed by defects in germline organization in him-17 mutants grown at high temperature (25°) and by a synthetic tumorous germline phenotype in glp-1(ar202); him-17 mutants at 15°.     

Differences in motivations and weight loss behaviors in young adults and older adults in the national weight control registry

Objective:

The goal of this study was to compare young adults (YA) and older adults (OA) in the National Weight Control Registry on motivations for weight loss and weight‐loss behaviors.

Design and Methods:

Participants (n = 2,964, 82% female, 94% White, BMI = 24.8 ± 4.4) were divided into two age groups (18‐35 vs. 36‐50) and compared on motivations, strategies for weight loss, diet, physical activity (PA), and the three‐factor eating questionnaire.

Results:

YA were 28.6% of the sample (n = 848). YA and OA achieved similar weight losses (P = 0.38), but duration of maintenance was less in YA (43 vs. 58 months, P < 0.001). YA were more likely to cite appearance and social motivations for weight loss, were less motivated by health, and were less likely to report a medical trigger for weight loss (P's < 0.001). YA were more likely to use exercise classes and to lose weight on their own, and less likely to use a commercial program (P's < 0.001). YA reported engaging in more high‐intensity PA (P = 0.001). There were no group differences in total calories consumed (P = 0.47), or percent calories from fat (P = 0.97), alcohol (P = 0.52), or sugar‐sweetened beverages (P = 0.26).

Conclusions:

YA successful weight losers (SWL) are motivated more by appearance and social influences than OA, and physical activity appears to play an important role in their weight‐loss efforts. The differences reported by YA and OA SWL should be considered when developing weight‐loss programs for YA.     

Development of pseudorabies virus strains expressing red fluorescent proteins: new tools for multisynaptic labeling applications

The transsynaptic retrograde transport of the pseudorabies virus Bartha (PRV-Bartha) strain has become an important neuroanatomical tract-tracing technique. Recently, dual viral transneuronal labeling has been introduced by employing recombinant strains of PRV-Bartha engineered to express different reporter proteins. Dual viral transsynaptic tracing has the potential of becoming an extremely powerful method for defining connections of single neurons to multiple neural circuits in the brain. However, the present use of recombinant strains of PRV expressing different reporters that are driven by different promoters, inserted in different regions of the viral genome, and detected by different methods limits the potential of these recombinant virus strains as useful reagents. We previously constructed and characterized PRV152, a PRV-Bartha derivative that expresses the enhanced green fluorescent protein. The development of a strain isogenic to PRV152 and differing only in the fluorescent reporter would have great utility for dual transsynaptic tracing. In this report, we describe the construction, characterization, and application of strain PRV614, a PRV-Bartha derivative expressing a novel monomeric red fluorescent protein, mRFP1. In contrast to viruses expressing DsRed and DsRed2, PRV614 displayed robust fluorescence both in cell culture and in vivo following transsynaptic transport through autonomic circuits afferent to the eye. Transneuronal retrograde dual PRV labeling has the potential to be a powerful addition to the neuroanatomical tools for investigation of neuronal circuits; the use of strain PRV614 in combination with strain PRV152 will eliminate many of the pitfalls associated with the presently used pairs of PRV recombinants.     

Crystal Structure of the GTPase-activating Protein-related Domain from IQGAP1

IQGAP1 is a 190-kDa molecular scaffold containing several domains required for interaction with numerous proteins. One domain is homologous to Ras GTPase-activating protein (GAP) domains. However, instead of accelerating hydrolysis of bound GTP on Ras IQGAP1, using its GAP-related domain (GRD) binds to Cdc42 and Rac1 and stabilizes their GTP-bound states. We report here the crystal structure of the isolated IQGAP1 GRD. Despite low sequence conservation, the overall structure of the GRD is very similar to the GAP domains from p120 RasGAP, neurofibromin, and SynGAP. However, instead of the catalytic “arginine finger” seen in functional Ras GAPs, the GRD has a conserved threonine residue. GRD residues 1099–1129 have no structural equivalent in RasGAP and are seen to form an extension at one end of the molecule. Because the sequence of these residues is highly conserved, this region likely confers a functionality particular to IQGAP family GRDs. We have used isothermal titration calorimetry to demonstrate that the isolated GRD binds to active Cdc42. Assuming a mode of interaction similar to that displayed in the Ras-RasGAP complex, we created an energy-minimized model of Cdc42·GTP bound to the GRD. Residues of the GRD that contact Cdc42 map to the surface of the GRD that displays the highest level of sequence conservation. The model indicates that steric clash between threonine 1046 with the phosphate-binding loop and other subtle changes would likely disrupt the proper geometry required for GTP hydrolysis.The small GTPase Ras functions as a binary switch in cell signaling processes. When bound to GTP, Ras is able to interact with effector proteins, including Raf kinase, and alter their activities. Ras signaling is terminated when bound GTP is hydrolyzed to GDP and inorganic phosphate. The basal rate of GTP hydrolysis on Ras is quite slow (∼1.2 × 10^–4 s^–1), but this rate of hydrolysis can be enhanced ∼10⁵-fold by interaction with a GTPase-activating protein (GAP)² (1). Several RasGAPs have been identified to date including p120 RasGAP and neurofibromin (NF1). The Rho family of Ras-related small GTPases also function as binary switches in cell signaling processes. Whereas the intrinsic rate of GTP hydrolysis on Rho proteins is faster than Ras, this rate can also be stimulated by interaction with a RhoGAP. Examination of the structures of the GAP domains of p120RasGAP (2), neurofibromin (3), SynGAP (4), and the GAP domains from the RhoGAPs p50 RhoGAP and the Bcr homology domain of phosphatidylinositol 3-kinase (5, 6) indicates that although ostensibly different, these all-helical domains are structurally related (7).IQGAP1 was discovered by chance during an attempt to isolate novel matrix metalloproteinases (8). Analysis reveals that the protein contains several discrete domains and motifs including a region containing four isoleucine- and glutamine-rich motifs (IQ repeats) and a region with sequence homology to the Ras-specific GAP domains of p120RasGAP, NF1, and SynGAP (2–4, 8). Subsequently, two homologs, IQGAP2 and IQGAP3, have been discovered. The IQ repeats have been shown to mediate binding to calmodulin and calmodulin-like proteins (e.g. S100, myosin essential light chain), whereas the GAP-related domain (GRD) does not appear to bind to Ras but instead is necessary for binding to the Rho family GTPases Cdc42 and Rac1, primarily in their active forms (9–11). However, instead of accelerating hydrolysis of GTP, IQGAP1 preserves the activated states of Cdc42 and Rac1 to the extent that overexpression of IQGAP1 in cells increases the levels of active GTPase (12). Because IQGAP1 expression increases the level of activated Cdc42, initially there was some confusion as to whether the protein might not represent a novel guanine nucleotide exchange factor. However it now appears that IQGAP1 is an effector of Cdc42 and Rac1 and preserves their activated states by tightly binding to the GTPases and stabilizing them in a conformation not conducive to GTP hydrolysis. IQGAP1 appears to be such an important effector for Cdc42 that abrogation of binding to IQGAP1 not only reduces the levels of active Cdc42, it also reduces membrane-localized Cdc42 and the cellular response to bradykinin (12).A growing body of evidence implicates IQGAP1 in carcinogenesis. Expression of IQGAP1 increases during the transition from a minimally to a highly metastastic form of melanoma, and IQGAP1 has been found to be overexpressed in ovarian, breast, lung, and colorectal cancers (13–17). In vitro, overexpressed IQGAP1 enhances cell motility and invasiveness in a process that requires Cdc42 and Rac (18). β-Catenin is one of the many binding partners of IQGAP1 identified to date. IQGAP1 has been shown to bind to β-catenin and interfere with β-catenin binding to α-catenin, an interaction necessary for stable cell-cell adhesion (19). Another study found that IQGAP2 knock-out mice overexpress IQGAP1 and developage-dependent liver cancer and apoptosis (20).To better understand how a protein domain homologous to others that accelerate GTP hydrolysis can function as an effector and preserve the GTP-bound state, we have determined the x-ray structure of the IQGAP1 GRD. Despite low sequence identity, the GRD structure is quite similar to the GAP domains of p120, neurofibromin, and SynGAP; however, unlike those domains, the GRD possesses a conserved threonine in place of the catalytic arginine finger and has a 31-residue insertion that projects from one end of the molecule. Using the coordinates of Ras·GDP·AlF₃ in complex with the GAP domain of p120, we built a model of Cdc42·GTP bound to the GRD. The model indicates that a steric clash between the conserved Thr¹⁰⁴⁶ and the phosphate-binding loop of Cdc42 and other subtle changes within the active site would likely preclude nucleotide hydrolysis. Sequence conservation mapped to the surface of the GRD indicates that the surface with the highest degree of conservation overlaps with the surface that makes contacts to Cdc42 in the model.     

Conformational stability and folding mechanisms of dimeric proteins

The folding of multisubunit proteins is of tremendous biological significance since the large majority of proteins exist as protein-protein complexes. Extensive experimental and computational studies have provided fundamental insights into the principles of folding of small monomeric proteins. Recently, important advances have been made in extending folding studies to multisubunit proteins, in particular homodimeric proteins. This review summarizes the equilibrium and kinetic theory and models underlying the quantitative analysis of dimeric protein folding using chemical denaturation, as well as the experimental results that have been obtained. Although various principles identified for monomer folding also apply to the folding of dimeric proteins, the effects of subunit association can manifest in complex ways, and are frequently overlooked. Changes in molecularity typically give rise to very different overall folding behaviour than is observed for monomeric proteins. The results obtained for dimers have provided key insights pertinent to understanding biological assembly and regulation of multisubunit proteins. These advances have set the stage for future advances in folding involving protein-protein interactions for natural multisubunit proteins and unnatural assemblies involved in disease.     

Hyperkalaemia,not apoptosis,accurately predicts insect chilling injury

There is a growing appreciation that insect distribution and abundance are associated with the limits of thermal tolerance, but the physiology underlying thermal tolerance remains poorly understood. Many insects, like the migratory locust (Locusta migratoria), suffer a loss of ion and water balance leading to hyperkalaemia (high extracellular [K⁺]) in the cold that indirectly causes cell death. Cells can die in several ways under stress, and how they die is of critical importance to identifying and understanding the nature of thermal adaptation. Whether apoptotic or necrotic cell death pathways are responsible for low-temperature injury is unclear. Here, we use a caspase-3 specific assay to indirectly quantify apoptotic cell death in three locust tissues (muscle, nerves and midgut) following prolonged chilling and recovery from an injury-inducing cold exposure. Furthermore, we obtain matching measurements of injury, extracellular [K⁺] and muscle caspase-3 activity in individual locusts to gain further insight into the mechanistic nature of chilling injury. We found a significant increase in muscle caspase-3 activity, but no such increase was observed in either nervous or gut tissue from the same animals, suggesting that chill injury primarily relates to muscle cell death. Levels of chilling injury measured at the whole animal level, however, were strongly correlated with the degree of haemolymph hyperkalaemia, and not apoptosis. These results support the notion that cold-induced ion balance disruption triggers cell death but also that apoptosis is not the main form of cell damage driving low-temperature injury.     

Ordered assembly of the V(D)J synaptic complex ensures accurate recombination

Recombination of gene segments at the immunoglobulin and T-cell receptor loci requires that the RAG1 and RAG2 proteins bring together DNA signal sequences (RSSs) with 12- and 23-bp spacers into a synaptic complex and cleave the DNA. A RAG1/2 multimer that can cleave both signals is shown to assemble on an isolated RSS, and the complementary RSS enters this complex as naked DNA. When RAG1/2 is allowed to bind 12 and 23 RSSs separately prior to their mixing, synaptic complex assembly and cleavage activity are greatly reduced, indicating that only a complex initially assembled on a single RSS leads to productive cleavage. RAG1/2 complexes assembled on 12 RSSs will only incorporate 23 partners, while complexes assembled on 23 RSSs show a 5- to 6-fold preference for 12 partners. Thus, initial assembly on a 12 RSS most accurately reflects the strict 12/23 coupled cleavage observed in the cell. Additional cellular factors such as chromatin may ensure that RAG1/2 first assembles on a 12 RSS, and then a free 23 RSS enters to activate cleavage.