Muscle-directed mechanosensory feedback activates egg-laying circuit activity and behavior in Caenorhabditis elegans

Mechanosensory feedback of the internal reproductive state drives decisions about when and where to reproduce.1 For instance, stretch in the Drosophila reproductive tract produced by artificial distention or from accumulated eggs regulates the attraction to acetic acid to ensure optimal oviposition.2 How such mechanosensory feedback modulates neural circuits to coordinate reproductive behaviors is incompletely understood. We previously identified a stretch-dependent homeostat that regulates egg laying in Caenorhabditis elegans. Sterilized animals lacking eggs show reduced Ca2+ transient activity in the presynaptic HSN command motoneurons that drive egg-laying behavior, while animals forced to accumulate extra eggs show dramatically increased circuit activity that restores egg laying.3 Interestingly, genetic ablation or electrical silencing of the HSNs delays, but does not abolish, the onset of egg laying,3,4,5 with animals recovering vulval muscle Ca2+ transient activity upon egg accumulation.6 Using an acute gonad microinjection technique to mimic changes in pressure and stretch resulting from germline activity and egg accumulation, we find that injection rapidly stimulates Ca2+ activity in both neurons and muscles of the egg-laying circuit. Injection-induced vulval muscle Ca2+ activity requires L-type Ca2+ channels but is independent of presynaptic input. Conversely, injection-induced neural activity is disrupted in mutants lacking the vulval muscles, suggesting "bottom-up" feedback from muscles to neurons. Direct mechanical prodding activates the vulval muscles, suggesting that they are the proximal targets of the stretch-dependent stimulus. Our results show that egg-laying behavior in C. elegans is regulated by a stretch-dependent homeostat that scales postsynaptic muscle responses with egg accumulation in the uterus.

Serotonin signals through postsynaptic Gαq, Trio RhoGEF, and diacylglycerol to promote Caenorhabditis elegans egg-laying circuit activity and behavior

Activated Gαq signals through phospholipase-Cβ and Trio, a Rho GTPase exchange factor (RhoGEF), but how these distinct effector pathways promote cellular responses to neurotransmitters like serotonin remains poorly understood. We used the egg-laying behavior circuit of Caenorhabditis elegans to determine whether phospholipase-Cβ and Trio mediate serotonin and Gαq signaling through independent or related biochemical pathways. Our genetic rescue experiments suggest that phospholipase-Cβ functions in neurons while Trio Rho GTPase exchange factor functions in both neurons and the postsynaptic vulval muscles. While Gαq, phospholipase-Cβ, and Trio Rho GTPase exchange factor mutants fail to lay eggs in response to serotonin, optogenetic stimulation of the serotonin-releasing HSN neurons restores egg laying only in phospholipase-Cβ mutants. Phospholipase-Cβ mutants showed vulval muscle Ca2+ transients while strong Gαq and Trio Rho GTPase exchange factor mutants had little or no vulval muscle Ca2+ activity. Treatment with phorbol 12-myristate 13-acetate that mimics 1,2-diacylglycerol, a product of PIP2 hydrolysis, rescued egg-laying circuit activity and behavior defects of Gαq signaling mutants, suggesting both phospholipase-C and Rho signaling promote synaptic transmission and egg laying via modulation of 1,2-diacylglycerol levels. 1,2-Diacylglycerol activates effectors including UNC-13; however, we find that phorbol esters, but not serotonin, stimulate egg laying in unc-13 and phospholipase-Cβ mutants. These results support a model where serotonin signaling through Gαq, phospholipase-Cβ, and UNC-13 promotes neurotransmitter release, and that serotonin also signals through Gαq, Trio Rho GTPase exchange factor, and an unidentified, phorbol 12-myristate 13-acetate-responsive effector to promote postsynaptic muscle excitability. Thus, the same neuromodulator serotonin can signal in distinct cells and effector pathways to coordinate activation of a motor behavior circuit.

Directed movement changes coexistence outcomes in heterogeneous environments

Understanding mechanisms of coexistence is a central topic in ecology. Mathematical analysis of models of competition between two identical species moving at different rates of symmetric diffusion in heterogeneous environments show that the slower mover excludes the faster one. The models have not been tested empirically and lack inclusions of a component of directed movement toward favourable areas. To address these gaps, we extended previous theory by explicitly including exploitable resource dynamics and directed movement. We tested the mathematical results experimentally using laboratory populations of the nematode worm, Caenorhabditis elegans. Our results not only support the previous theory that the species diffusing at a slower rate prevails in heterogeneous environments but also reveal that moderate levels of a directed movement component on top of the diffusive movement allow species to coexist. Our results broaden the theory of species coexistence in heterogeneous space and provide empirical confirmation of the mathematical predictions.

Presynaptic Gαo (GOA-1) signals to depress command neuron excitability and allow stretch-dependent modulation of egg laying in Caenorhabditis elegans

Egg laying in the nematode worm Caenorhabditis elegans is a two-state behavior modulated by internal and external sensory input. We have previously shown that homeostatic feedback of embryo accumulation in the uterus regulates bursting activity of the serotonergic HSN command neurons that sustains the egg-laying active state. How sensory feedback of egg release signals to terminate the egg-laying active state is less understood. We find that Gαo, a conserved Pertussis Toxin-sensitive G protein, signals within HSN to inhibit egg-laying circuit activity and prevent entry into the active state. Gαo signaling hyperpolarizes HSN, reducing HSN Ca2+ activity and input onto the postsynaptic vulval muscles. Loss of inhibitory Gαo signaling uncouples presynaptic HSN activity from a postsynaptic, stretch-dependent homeostat, causing precocious entry into the egg-laying active state when only a few eggs are present in the uterus. Feedback of vulval opening and egg release activates the uv1 neuroendocrine cells which release NLP-7 neuropeptides which signal to inhibit egg laying through Gαo-independent mechanisms in the HSNs and Gαo-dependent mechanisms in cells other than the HSNs. Thus, neuropeptide and inhibitory Gαo signaling maintains a bi-stable state of electrical excitability that dynamically controls circuit activity in response to both external and internal sensory input to drive a two-state behavior output.

Identification of Toxicity Effects of Cu2O Materials on C. elegans as a Function of Environmental Ionic Composition

Previous work has shown that spherical CuO nanomaterials show negative effects on cell and animal physiology. The biological effects of Cu₂O materials, which posess unique chemical features compared to CuO nanomaterials and can be synthesized in a similarly large variety of shapes and sizes, are comparatively less studied. Here, we synthesized truncated octahedral Cu₂O particles and characterized their structure, stability, and physiological effects in the nematode worm animal model, Caenorhabditis elegans. Cu₂O particles were found to be generally stable in aqueous media, although the particles did show signs of oxidation and leaching of Cu²⁺ within hours in worm growth media. The particles were found to be especially sensitive to inorganic phosphate (PO₄ ^3-) found in standard NGM nematode growth medium. Cu₂O particles were observed being taken up into the nematode pharynx and detected in the lumen of the gut. Toxicity experiments revealed that treatment with Cu₂O particles caused a significant reduction in animal size and lifespan. These toxic effects resembled treatment with Cu²⁺, but measurements of Cu leaching, worm size, and long-term behavior experiments show the particles are more toxic than expected from Cu ion leaching alone. These results suggest worm ingestion of intact Cu₂O particles enhances their toxicity and behavior effects while particle exposure to environmental phosphate precipitates leached Cu²⁺ into biounavailable phosphate salts. Interestingly, the worms showed an acute avoidance of bacterial food with Cu₂O particles, suggesting that animals can detect chemical features of the particles and/or their breakdown products and actively avoid areas with them. These results will help to understand how specific, chemically-defined particles proposed for use in polluted soil and wastewater remediation affect animal toxicity and behaviors in their natural environment.

Serotonin and neuropeptides are both released by the HSN command neuron to initiate Caenorhabditis elegans egg laying

Neurons typically release both a small-molecule neurotransmitter and one or more neuropeptides, but how these two types of signal from the same neuron might act together remains largely obscure. For example, serotonergic neurons in mammalian brain express the neuropeptide Substance P, but it is unclear how this co-released neuropeptide might modulate serotonin signaling. We studied this issue in C. elegans, in which all serotonergic neurons express the neuropeptide NLP-3. The serotonergic Hermaphrodite Specific Neurons (HSNs) are command motor neurons within the egg-laying circuit which have been shown to release serotonin to initiate egg-laying behavior. We found that egg-laying defects in animals lacking serotonin were far milder than in animals lacking HSNs, suggesting that HSNs must release other signal(s) in addition to serotonin to stimulate egg laying. While null mutants for nlp-3 had only mild egg-laying defects, animals lacking both serotonin and NLP-3 had severe defects, similar to those of animals lacking HSNs. Optogenetic activation of HSNs induced egg laying in wild-type animals, and in mutant animals lacking either serotonin or NLP-3, but failed to induce egg laying in animals lacking both. We recorded calcium activity in the egg-laying muscles of animals lacking either serotonin, NLP-3, or both. The single mutants, and to a greater extent the double mutant, showed muscle activity that was uncoordinated and unable to expel eggs. Specifically, the vm2 muscles cells, which are direct postsynaptic targets of the HSN, failed to contract simultaneously with other egg-laying muscle cells. Our results show that the HSN neurons use serotonin and the neuropeptide NLP-3 as partially redundant co-transmitters that together stimulate and coordinate activity of the target cells onto which they are released.

Activity of the brain results from neurons communicating with each other using chemical signals. A typical neuron releases two kinds of chemical signals: a small molecule neurotransmitter, such as serotonin, and one or more small proteins, called neuropeptides. For example, neurons in the human brain that release serotonin, a neurotransmitter thought to be involved in depression, also release the neuropeptide Substance P. Neuroscientists have typically studied the effects of neurotransmitters and neuropeptides separately, without considering how these two types of signals from the same neuron might be integrated. Here we analyzed how specific neurons in the model organism C. elegans use both serotonin and a neuropeptide together. The Hermaphrodite Specific Neurons (HSNs) activate a small group of neurons and muscles to generate egg-laying behavior. Killing the HSNs resulted in animals unable to lay eggs, but we found that eliminating either serotonin or the neuropeptide resulted in HSNs that still remained able to activate egg laying. However, eliminating both serotonin and the neuropeptide resulted in HSNs unable to activate coordinated contractions of the egg-laying muscles. Our results show that in a living animal, serotonin acts in concert with a co-released neuropeptide to carry out its functions.

Photochemical Barcodes

A photochemical strategy to encode fluorescence signals in vivo with spatial control was designed around the unique properties of a photoactivatable borondipyrromethene (BODIPY). The photoinduced disconnection of two oxazines, flanking a single BODIPY, in two consecutive steps produces a mixture of three emissive molecules with resolved fluorescence inside polymer beads. The relative amounts and emission intensities of the three fluorophores can be regulated precisely in each bead by adjusting the dose of activating photons to mark individual particles with distinct codes of fluorescence signals. The visible wavelengths and mild illumination sufficient to induce these transformations permit the photochemical barcoding of beads also in living nematodes. Different regions of the same animal can be labeled with distinct barcodes to allow the monitoring of their dynamics for long times with no toxic effects. Thus, our photochemical strategy for the generation of fluorescence barcodes can produce multiple and distinguishable labels in the same biological sample to enable the spatiotemporal tracking of, otherwise indistinguishable, targets.

Mycobacterium tuberculosis infection among persons who inject drugs in San Diego, California

BACKGROUND

Persons who inject drugs (PWID) might be at increased risk for Mycobacterium tuberculosis infection and reactivation of latent tuberculous infection (LTBI) due to their injection drug use.

OBJECTIVES

To determine prevalence and correlates of M. tuberculosis infection among PWID in San Diego, California, USA.

METHODS

PWID aged 18 years underwent standardized interviews and serologic testing using an interferon-gamma release assay (IGRA) for LTBI and rapid point-of-care assays for human immunodeficiency virus (HIV) and hepatitis C virus (HCV) infections. Independent correlates of M. tuberculosis infection were identified using multivariable log-binomial regression.

RESULTS

A total of 500 participants met the eligibility criteria. The mean age was 43.2 years (standard deviation 11.6); most subjects were White (52%) or Hispanic (30.8%), and male (75%). Overall, 86.7% reported having ever traveled to Mexico. Prevalence of M. tuberculosis infection was 23.6%; 0.8% were co-infected with HIV and 81.7% were co-infected with HCV. Almost all participants (95%) had been previously tested for M. tuberculosis; 7.6% had been previously told they were infected. M. tuberculosis infection was independently associated with being Hispanic, having longer injection histories, testing HCV-positive, and correctly reporting that people with 'sleeping' TB cannot infect others.

CONCLUSIONS

Strategies are needed to increase awareness about and treatment for M. tuberculosis infection among PWID in the US/Mexico border region.

Ratiometric Calcium Imaging of Individual Neurons in Behaving Caenorhabditis Elegans

It has become increasingly clear that neural circuit activity in behaving animals differs substantially from that seen in anesthetized or immobilized animals. Highly sensitive, genetically encoded fluorescent reporters of Ca²⁺ have revolutionized the recording of cell and synaptic activity using non-invasive optical approaches in behaving animals. When combined with genetic and optogenetic techniques, the molecular mechanisms that modulate cell and circuit activity during different behavior states can be identified. Here we describe methods for ratiometric Ca²⁺ imaging of single neurons in freely behaving Caenorhabditis elegans worms. We demonstrate a simple mounting technique that gently overlays worms growing on a standard Nematode Growth Media (NGM) agar block with a glass coverslip, permitting animals to be recorded at high-resolution during unrestricted movement and behavior. With this technique, we use the sensitive Ca²⁺ reporter GCaMP5 to record changes in intracellular Ca²⁺ in the serotonergic Hermaphrodite Specific Neurons (HSNs) as they drive egg-laying behavior. By co-expressing mCherry, a Ca²⁺-insensitive fluorescent protein, we can track the position of the HSN within ~ 1 µm and correct for fluctuations in fluorescence caused by changes in focus or movement. Simultaneous, infrared brightfield imaging allows for behavior recording and animal tracking using a motorized stage. By integrating these microscopic techniques and data streams, we can record Ca²⁺ activity in the C. elegans egg-laying circuit as it progresses between inactive and active behavior states over tens of minutes.

Bioimaging with Macromolecular Probes Incorporating Multiple BODIPY Fluorophores

Seven macromolecular constructs incorporating multiple borondipyrromethene (BODIPY) fluorophores along a common poly(methacrylate) backbone with decyl and oligo(ethylene glycol) side chains were synthesized. The hydrophilic oligo(ethylene glycol) components impose solubility in aqueous environment on the overall assembly. The hydrophobic decyl chains effectively insulate the fluorophores from each other to prevent detrimental interchromophoric interactions and preserve their photophysical properties. As a result, the brightness of these multicomponent assemblies is approximately three times greater than that of a model BODIPY monomer. Such a high brightness level is maintained even after injection of the macromolecular probes in living nematodes, allowing their visualization with a significant improvement in signal-to-noise ratio, relative to the model monomer, and no cytotoxic or behavioral effects. The covalent scaffold of these macromolecular constructs also permits their subsequent conjugation to secondary antibodies. The covalent attachment of polymer and biomolecule does not hinder the targeting ability of the latter and the resulting bioconjugates can be exploited to stain the tubulin structure of model cells to enable their visualization with optimal signal-to-noise ratios. These results demonstrate that this particular structural design for the incorporation of multiple chromophores within the same covalent construct is a viable one to preserve the photophysical properties of the emissive species and enable the assembly of bioimaging probes with enhanced brightness.

Local neuropeptide signaling modulates serotonergic transmission to shape the temporal organization of C. elegans egg-laying behavior

Animal behaviors are often composed of distinct alternating behavioral states. Neuromodulatory signals are thought to be critical for establishing stable behavioral states and for orchestrating transitions between them. However, we have only a limited understanding of how neuromodulatory systems act in vivo to alter circuit performance and shape behavior. To address these questions, we have investigated neuromodulatory signaling in the context of Caenorhabditis elegans egg-laying. Egg-laying activity cycles between discrete states-short bursts of egg deposition (active phases) that alternate with prolonged quiescent periods (inactive phases). Here using genetic, pharmacological and optogenetic approaches for cell-specific activation and inhibition, we show that a group of neurosecretory cells (uv1) located in close spatial proximity to the egg-laying neuromusculature direct the temporal organization of egg-laying by prolonging the duration of inactive phases. We demonstrate that the modulatory effects of the uv1 cells are mediated by peptides encoded by the nlp-7 and flp-11 genes that act locally to inhibit circuit activity, primarily by inhibiting vesicular release of serotonin from HSN motor neurons. This peptidergic inhibition is achieved, at least in part, by reducing synaptic vesicle abundance in the HSN motor neurons. By linking the in vivo actions of specific neuropeptide signaling systems with the generation of stable behavioral outcomes, our study reveals how cycles of neuromodulation emanating from non-neuronal cells can fundamentally shape the organization of a behavioral program.

Activity of the C. elegans egg-laying behavior circuit is controlled by competing activation and feedback inhibition

Like many behaviors, Caenorhabditis elegans egg laying alternates between inactive and active states. To understand how the underlying neural circuit turns the behavior on and off, we optically recorded circuit activity in behaving animals while manipulating circuit function using mutations, optogenetics, and drugs. In the active state, the circuit shows rhythmic activity phased with the body bends of locomotion. The serotonergic HSN command neurons initiate the active state, but accumulation of unlaid eggs also promotes the active state independent of the HSNs. The cholinergic VC motor neurons slow locomotion during egg-laying muscle contraction and egg release. The uv1 neuroendocrine cells mechanically sense passage of eggs through the vulva and release tyramine to inhibit egg laying, in part via the LGC-55 tyramine-gated Cl^- channel on the HSNs. Our results identify discrete signals that entrain or detach the circuit from the locomotion central pattern generator to produce active and inactive states.

DOI:http://dx.doi.org/10.7554/eLife.21126.001

It has been said that if the human brain were so simple that we could understand it, we would be so simple that we couldn’t. This quote neatly captures the challenge of working out how 80 billion neurons collectively generate our thoughts and behavior. Fortunately, the nervous system is also organized into simpler units called circuits. Each consists of a relatively small number of neurons, which communicate with one another to control as little as a single behavior. These circuits should in principle be simple enough for us to understand, particularly if we study them in nervous systems less complex than our own.

Despite this, there is currently not a single circuit in any organism in which we can explain how communication between individual neurons generates behavior. Collins et al. therefore set out to characterize a simple neural circuit in one of the simplest model organisms: the egg-laying circuit of the worm C. elegans.

Using mutations, drugs and molecular genetic techniques, Collins et al. systematically altered the activity and signaling of each of the neurons within the egg-laying circuit. The experiments revealed that cells called command neurons trigger egg laying by producing signals that switch on the rest of the circuit. Once activated, the circuit is able to respond to waves of activity from a second circuit – called the central pattern generator – that also controls the worm’s movement. Finally, laying an egg activates a third set of neurons, which release a signal that returns the circuit to its inactive state.

The use of distinct signals and neurons to activate the circuit, to coordinate its ongoing activity, and to inactivate the circuit when its task is complete also applies to many other neural circuits. Now that these signals have been identified in one circuit, it should be possible to build on these findings to better understand how others work.

DOI:http://dx.doi.org/10.7554/eLife.21126.002

Writing Apprehension and Academic Procrastination among Graduate Students

Academic procrastination has been associated with both fear of failure and task aversiveness. Researchers have reported that most undergraduate and graduate students delay academic tasks. Among the latter, a large proportion report procrastination in writing term papers. Such procrastination may originate from and lead to anxiety about writing so the present purpose was to investigate the relationship between scores on Daly and Miller's 1975 Writing Apprehension Test and on the two dimensions, i.e., fear of failure and task aversiveness, of Solomon and Rothblum's 1984 Procrastination Assessment Scale-Students. Participants were 135 graduate students of varied disciplinary backgrounds. Correlations between writing apprehension and academic procrastination stemmed from fear of failure (.29) and task aversiveness (.41). Implications are discussed.

Quantitative determination of sporozoites and circumsporozoite antigen in mosquitoes infected withPlasmodium falciparumorP. vivax

It is essential for malariologists and researchers to have simple and accurate means of assessing the threat of Plasmodium parasites. An attempt was therefore made to re-standardize one of the circumsporozoite (CS) ELISA that can be used to detect and quantify the circumsporozoite antigens of P. falciparum and P. vivax. A two-site, 'sandwich' ELISA based on a monoclonal antibody was used to test for the CS antigen and sporozoites of each Plasmodium species simultaneously. Using the resultant optical-density values, standard curves, that permit the number of sporozoites in an infected mosquito to be estimated from the quantification of the CS antigen, were constructed. Using these plots and the CS ELISA, the presence of just 12.5 sporozoites (i.e. 0.8 pg CS antigen) of P. falciparum, four sporozoites (3.2 pg antigen) of P. vivax-210 or 12.5 sporozoites (32.0 pg antigen) of P. vivax-247 could be demonstrated.

LIN-12/Notch signaling instructs postsynaptic muscle arm development by regulating UNC-40/DCC and MADD-2 in Caenorhabditis elegans

The diverse cell types and the precise synaptic connectivity between them are the cardinal features of the nervous system. Little is known about how cell fate diversification is linked to synaptic target choices. Here we investigate how presynaptic neurons select one type of muscles, vm2, as a synaptic target and form synapses on its dendritic spine-like muscle arms. We found that the Notch-Delta pathway was required to distinguish target from non-target muscles. APX-1/Delta acts in surrounding cells including the non-target vm1 to activate LIN-12/Notch in the target vm2. LIN-12 functions cell-autonomously to up-regulate the expression of UNC-40/DCC and MADD-2 in vm2, which in turn function together to promote muscle arm formation and guidance. Ectopic expression of UNC-40/DCC in non-target vm1 muscle is sufficient to induce muscle arm extension from these cells. Therefore, the LIN-12/Notch signaling specifies target selection by selectively up-regulating guidance molecules and forming muscle arms in target cells.

DOI:http://dx.doi.org/10.7554/eLife.00378.001

The development of the nervous system involves the formation of complex networks of connections between diverse cell types, such as motor neurons, interneurons and pyramidal cells. However, the mechanisms by which individual cells are programmed to acquire particular identities, and how they are instructed to form connections with other specific cells, remain unclear.

In many species, the Notch signaling pathway has a role in setting up these networks. Notch is a transmembrane protein, which means that it has one component inside the cell and another outside. When a ligand binds to the extracellular part of Notch, this causes the receptor to break in two. The intracellular domain then travels to the nucleus where it can influence gene expression.

The nematode worm (C. elegans), which has two Notch receptors, is often used to study the formation of neuronal networks because each worm has only around 300 neurons, and they are connected in roughly the same way in each worm. C. elegans relies on two types of cell that are very similar to each other—type-1 and type-2 vulval muscle cells—to lay eggs, and the neurons that trigger egg-laying form synaptic connections on specialized structures called muscle arms. However, these structures are found only in type-2 vulval muscle.

To investigate the mechanisms underlying the formation of the egg-laying circuit, Li et al. screened large numbers of mutant worms to find animals that lacked muscle arms. They identified a number of such mutants, which laid fewer eggs compared to wild-type worms, and found that they all had mutations in genes that encode for proteins or ligands that are involved in the LIN-12/Notch pathway. This pathway mediates cell–cell interactions that help to specify cell fates.

Li et al. showed that type-2 vulval muscle cells develop muscle arms when their neighbors—type-1 vulval muscle cells and vulval epithelial cells—produce enough ligand to activate the LIN-12 Notch receptor on the type-2 vulval muscle cells. They also identified two of the downstream targets of LIN-12, and found that artificially expressing one of these in type-1 vulval muscle cells is sufficient to trigger the formation of muscle arms.

The work of Li et al. provides further evidence that the Notch signalling pathway, which is well known for its role in early development, also acts at later developmental stages to determine cell fate and patterns of connectivity.

DOI:http://dx.doi.org/10.7554/eLife.00378.002

Trans-SNARE complex assembly and yeast vacuole membrane fusion

cis-SNARE complexes (anchored in one membrane) are disassembled by Sec17p (alpha-SNAP) and Sec18p (NSF), permitting the unpaired SNAREs to assemble in trans. We now report a direct assay of trans-SNARE complex formation during yeast vacuole docking. SNARE complex assembly and fusion is promoted by high concentrations of the SNARE Vam7p or Nyv1p or by addition of HOPS (homotypic fusion and vacuole protein sorting), a Ypt7p (Rab)-effector complex with a Sec1/Munc18-family subunit. Inhibitors that target Ypt7p, HOPS, or key regulatory lipids prevent trans-SNARE complex assembly and ensuing fusion. Strikingly, the lipid ligand MED (myristoylated alanine-rich C kinase substrate effector domain) or elevated concentrations of Sec17p, which can displace HOPS from SNARE complexes, permit full trans-SNARE pairing but block fusion. These findings suggest that efficient fusion requires trans-SNARE complex associations with factors such as HOPS and subsequent regulated lipid rearrangements.

Stringent 3Q.1R composition of the SNARE 0-layer can be bypassed for fusion by compensatory SNARE mutation or by lipid bilayer modification

SNARE proteins form bundles of four alpha-helical SNARE domains with conserved polar amino acids, 3Q and 1R, at the "0-layer" of the bundle. Previous studies have confirmed the importance of 3Q.1R for fusion but have not shown whether it regulates SNARE complex assembly or the downstream functions of assembled SNAREs. Yeast vacuole fusion requires regulatory lipids (ergosterol, phosphoinositides, and diacylglycerol), the Rab Ypt7p, the Rab-effector complex HOPS, and 4 SNAREs: the Q-SNAREs Vti1p, Vam3p, and Vam7p and the R-SNARE Nyv1p. We now report that alterations in the 0-layer Gln or Arg residues of Vam7p or Nyv1p, respectively, strongly inhibit fusion. Vacuoles with wild-type Nyv1p show exquisite discrimination for the wild-type Vam7p over Vam7(Q283R), yet Vam7(Q283R) is preferred by vacuoles with Nyv1(R191Q). Rotation of the position of the arginine in the 0-layer increases the K(m) for Vam7p but does not affect the maximal rate of fusion. Vam7(Q283R) forms stable 2Q.2R complexes that do not promote fusion. However, fusion is restored by the lipophilic amphiphile chlorpromazine or by the phospholipase C inhibitor U73122, perturbants of the lipid phase of the membrane. Thus, SNARE function as regulated by the 0-layer is intimately coupled to the lipids, which must rearrange for fusion.

Purification of active HOPS complex reveals its affinities for phosphoinositides and the SNARE Vam7p

Coupling of Rab GTPase activation and SNARE complex assembly during membrane fusion is poorly understood. The homotypic fusion and vacuole protein sorting (HOPS) complex links these two processes: it is an effector for the vacuolar Rab GTPase Ypt7p and is required for vacuolar SNARE complex assembly. We now report that pure, active HOPS complex binds phosphoinositides and the PX domain of the vacuolar SNARE protein Vam7p. These binding interactions support HOPS complex association with the vacuole and explain its enrichment at the same microdomains on docked vacuoles as phosphoinositides, Ypt7p, Vam7p, and the other SNARE proteins. Concentration of the HOPS complex at these microdomains may be a key factor for coupling Rab GTPase activation to SNARE complex assembly.

Sec17p and HOPS, in distinct SNARE complexes, mediate SNARE complex disruption or assembly for fusion

SNARE functions during membrane docking and fusion are regulated by Sec1/Munc18 (SM) chaperones and Rab/Ypt GTPase effectors. These functions for yeast vacuole fusion are combined in the six-subunit HOPS complex. HOPS facilitates Ypt7p nucleotide exchange, is a Ypt7p effector, and contains an SM protein. We have dissected the associations and requirements for HOPS, Ypt7p, and Sec17/18p during SNARE complex assembly. Vacuole SNARE complexes bind either Sec17p or the HOPS complex, but not both. Sec17p and its co-chaperone Sec18p disassemble SNARE complexes. Ypt7p regulates the reassembly of unpaired SNAREs with each other and with HOPS, forming HOPS.SNARE complexes prior to fusion. After HOPS.SNARE assembly, lipid rearrangements are still required for vacuole content mixing. Thus, Sec17p and HOPS have mutually exclusive interactions with vacuole SNAREs to mediate disruption of SNARE complexes or their assembly for docking and fusion. Sec17p may displace HOPS from SNAREs to permit subsequent rounds of fusion.

Quantification of Plasmodium malariae infection in mosquito vectors

Plasmodium malariae occurs in various tropical regions throughout the world and causes low, yet significant, levels of morbidity in human populations. One means of studying the ecology and frequency of this parasite is by measuring sporozoite loads in the salivary glands of infected mosquitoes. An effective, species-specific test that can be used to detect the presence of sporozoites in mosquitoes is the circumsporozoite ELISA. The aim of the present study was to standardize the circumsporozoite ELISA for P.malariae, by setting quantification parameters using, as antigen, either a synthetic peptide or extracts of whole sporozoites. The standard quantification curves produced indicated that the assay had a lower threshold of sensitivity of 250 sporozoites in a 50-microl sample, equivalent to about 1250 sporozoites in a mosquito.

A soluble SNARE drives rapid docking, bypassing ATP and Sec17/18p for vacuole fusion

Membrane fusion requires priming, the disassembly of cis-SNARE complexes by the ATP-driven chaperones Sec18/17p. Yeast vacuole priming releases Vam7p, a soluble SNARE. Vam7p reassociation during docking allows trans-SNARE pairing and fusion. We now report that recombinant Vam7p (rVam7p) enters into complex with other SNAREs in vitro and bypasses the need for Sec17p, Sec18p, and ATP. Thus, the sole essential function of vacuole priming in vitro is the release of Vam7p from cis-SNARE complexes. In 'bypass fusion', without ATP but with added rVam7p, there are sufficient unpaired vacuolar SNAREs Vam3p, Vti1p, and Nyv1p to interact with Vam7p and support fusion. However, active SNARE proteins are not sufficient for bypass fusion. rVam7p does not bypass requirements for Rho GTPases,Vps33p, Vps39p, Vps41p, calmodulin, specific lipids, or Vph1p, a subunit of the V-ATPase. With excess rVam7p, reduced levels of PI(3)P or functional Ypt7p suffice for bypass fusion. High concentrations of rVam7p allow the R-SNARE Ykt6p to substitute for Nyv1p for fusion; this functional redundancy among vacuole SNAREs may explain why nyv1delta strains lack the vacuole fragmentation seen with mutants in other fusion catalysts.

Hierarchy of protein assembly at the vertex ring domain for yeast vacuole docking and fusion

Vacuole tethering, docking, and fusion proteins assemble into a "vertex ring" around the apposed membranes of tethered vacuoles before catalyzing fusion. Inhibitors of the fusion reaction selectively interrupt protein assembly into the vertex ring, establishing a causal assembly hierarchy: (a) The Rab GTPase Ypt7p mediates vacuole tethering and forms the initial vertex ring, independent of t-SNAREs or actin; (b) F-actin disassembly and GTP-bound Ypt7p direct the localization of other fusion factors; (c) The t-SNAREs Vam3p and Vam7p regulate each other's vertex enrichment, but do not affect Ypt7p localization. The v-SNARE Vti1p is enriched at vertices by a distinct pathway that is independent of the t-SNAREs, whereas both t-SNAREs will localize to vertices when trans-pairing of SNAREs is blocked. Thus, trans-SNARE pairing is not required for SNARE vertex enrichment; and (d) The t-SNAREs regulate the vertex enrichment of both G-actin and the Ypt7p effector complex for homotypic fusion and vacuole protein sorting (HOPS). In accord with this hierarchy concept, the HOPS complex, at the end of the vertex assembly hierarchy, is most enriched at those vertices with abundant Ypt7p, which is at the start of the hierarchy. Our findings provide a unique view of the functional relationships between GTPases, SNAREs, and actin in membrane fusion.

Extensive multiple test centre evaluation of the VecTest malaria antigen panel assay

To determine which species and populations of Anopheles transmit malaria in any given situation, immunological assays for malaria sporozoite antigen can replace traditional microscopical examination of freshly dissected Anopheles. We developed a wicking assay for use with mosquitoes that identifies the presence or absence of specific peptide epitopes of circumsporozoite (CS) protein of Plasmodium falciparum and two strains of Plasmodium vivax (variants 210 and 247). The resulting assay (VecTest Malaria) is a rapid, one-step procedure using a 'dipstick' test strip capable of detecting and distinguishing between P. falciparum and P. vivax infections in mosquitoes. The objective of the present study was to test the efficacy, sensitivity, stability and field-user acceptability of this wicking dipstick assay. In collaboration with 16 test centres world-wide, we evaluated more than 40 000 units of this assay, comparing it to the standard CS ELISA. The 'VecTest Malaria' was found to show 92% sensitivity and 98.1% specificity, with 97.8% accuracy overall. In accelerated storage tests, the dipsticks remained stable for > 15 weeks in dry conditions up to 45 degrees C and in humid conditions up to 37 degrees C. Evidently, this quick and easy dipstick test performs at an acceptable level of reliability and offers practical advantages for field workers needing to make rapid surveys of malaria vectors.

Career involvement and family involvement as moderators of relationships between work-family conflict and withdrawal from a profession

This study extended prior analyses by J. H. Greenhaus, K. M. Collins, R. Singh, and S. Parasuraman (1997) by examining relationships between 2 directions of work-family conflict (work-to-family conflict and family-to-work conflict) and withdrawal from public accounting. The sample consisted of 199 members of the American Institute of Certified Public Accountants (135 men and 64 women) who were married or in a long-term relationship and who had 1 or more children. It was found that work-to-family conflict (but not family-to-work conflict) was positively related to withdrawal intentions. In addition, relationships of work-to-family conflict with withdrawal intentions and withdrawal behavior were stronger for individuals who were relatively uninvolved in their careers than for those who were highly involved in their careers. The implications of the findings for future research are discussed.

hCds1-mediated phosphorylation of BRCA1 regulates the DNA damage response

Mutations in the BRCA1 (ref. 1) tumour suppressor gene are found in almost all of the families with inherited breast and ovarian cancers and about half of the families with only breast cancer. Although the biochemical function of BRCA1 is not well understood, it is important for DNA damage repair and cell-cycle checkpoint. BRCA1 exists in nuclear foci but is hyperphosphorylated and disperses after DNA damage. It is not known whether BRCA1 phosphorylation and dispersion and its function in DNA damage response are related. In yeast the DNA damage response and the replication-block checkpoint are mediated partly through the Cds1 kinase family. Here we report that the human Cds1 kinase (hCds1/Chk2) regulates BRCA1 function after DNA damage by phosphorylating serine 988 of BRCA1. We show that hCds1 and BRCA1 interact and co-localize within discrete nuclear foci but separate after gamma irradiation. Phosphorylation of BRCA1 at serine 988 is required for the release of BRCA1 from hCds1. This phosphorylation is also important for the ability of BRCA1 to restore survival after DNA damage in the BRCA1-mutated cell line HCC1937.

Clinical comparison of the SITE IRAS hand-held interferometer and Haag-Streit Lotmar visometer

The preoperative testing of retinal acuity was evaluated using two instruments in each of 35 eyes having extracapsular cataract extraction. Retinal acuity was measured using the SITE IRAS hand-held interferometer and the Haag-Streit Lotmar visometer. The postoperative findings are given for comparisons of final acuity, prediction, and instrument evaluation. The results showed predicted acuity to be within two lines of the final acuity in 57.1% of eyes with the Haag-Streit unit and in 42.8% of eyes with the SITE instrument. The instrument differences were more in procedure than in results.

Categorization of hospital emergency services--developing valid criteria

In a pilot project sponsored by the California State Emergency Medical Services Authority, validated, verifiable criteria were developed for the vertical categorization of hospital emergency services in 11 different groupings of medical and surgical emergencies. We describe the development of an assessment process and categorization criteria to identify the most appropriate receiving facility for interfacility transfer and, in selected instances, field triage of patients with different levels of severity of illness or injury. We propose that this facility assessment project be used in the critical care planning process for the eventual vertical categorization of hospital emergency services in California and as a template for similar projects in other states.

Outpatient termination of pregnancy: halothane or alfentanil-supplemented anaesthesia

Inhalation anaesthesia with halothane was compared with i.v. alfentanil in 66 unpremedicated patients undergoing suction termination of pregnancy as outpatients. Blood loss was significantly greater in the halothane group with a mean loss of 213 ml, compared with a mean loss of 89.8 ml in the alfentanil group. There was a greater frequency of nausea and vomiting in the alfentanil group, but no reduction in abdominal pain or need for analgesia after operation. Positive relationships were found between blood loss and duration of anaesthesia and between blood loss and gestational age in the halothane group, but not in the alfentanil group. We conclude that alfentanil-supplemented anaesthesia is satisfactory for suction termination of pregnancy when rapid recovery is required or the duration of the procedure is likely to be long, but that halothane anaesthesia cannot be recommended, especially if the procedure is long.

Use of alfentanil in short anaesthetic procedures

The pharmacokinetics of alfentanil, a new and very short-acting opioid, are discussed. Its use in day-case gynaecological procedures is described, and the results of the initial study presented. Alfentanil is a valuable adjunct to anaesthesia for day-case surgery and for short, painful procedures.

Comparison of atracurium and alcuronium in day-case gynaecological surgery

Alcuronium and atracurium were used on a randomised basis as part of the anaesthetic technique for out-patient gynaecological laparoscopy. Conditions for intubation and relaxation were similar but there was a marked decrease in the incidence of minor postoperative sequelae in the atracurium group.

Postoperative morbidity following gynaecological outpatient laparoscopy. A reappraisal of the service

Fifty-six women having out-patient gynaecological laparoscopies were studied to determine anaesthetic problems and postoperative morbidity. It is concluded that the procedure is safe, and although the postoperative morbidity appears high it is very acceptable to the patient.

Studies of activating and nonactivating metal ion binding to yeast enolase

Measurements of binding of certain divalent cations to yeast apoenolase were made using a pH-meter, chromatography, a divalent cation electrode, and ultrafiltration. The binding of the activating metal ions Mg2+ and Co2+ and the nonactivator Ca2+ were studied as functions of the presence or absence of substrate/product, phosphate, and fluoride or level of Tb3+. The data suggest phosphate and fluoride increase Mg2+ binding but not Ca2+ binding. Substrate/product appears to increase Ca2+ binding as well as that of Mg2+ and Co2+. In the presence of substrate, Co2+ binding was 5-6 mol/mol dimer. In the absence of substrate/product, Tb3+ reduced Co2+ binding from 4 mol/mol to 2. These data are interpreted in terms of binding to "conformational," "catalytic" (substrate/product dependent), and "inhibitory" sites. Measurements of Tb3+ fluorescence quenching by Co2+ suggested that the distance between "conformational" sites on the two subunits was large, while the distance between "conformational" and "inhibitory" sites was ca. 17 +/- 4 A. Potentiometric titrations of apoenzyme with Ca2+ and Mg2+ showed that the metal ions produced the same proton release in the presence or absence of substrate/product. If phosphate and fluoride were present, then more protons were released if Ca2+ was the titrant rather than Mg2+, suggesting a difference in ionization state in the complex with the activating metal. Electron paramagnetic resonance studies of Co2+ binding to the various sites in the enzyme are presented. The Co2+ bound to all three sites appears to be high spin, consistent with a preponderance of oxyligands in an octahedral environment. Substrate, citrate, and a strongly binding substrate analogue strongly enhance the hyperfine structure of conformational Co2+. This is interpreted as the result of a change in interaction of an axial ligand to conformational Co2+ produced by carbon-3 of substrate or analogue.

Circular dichroism (CD) studies on yeast enolase: activation by divalent cations

The effect of divalent cations on the near ultraviolet circular dichroism (CD) spectrum of yeast enolase showed that calcium, magnesium, and nickel ions produced identical changes. This was interpreted as indicating that the cations bound to the same sites on the enzyme and produced identical changes in tertiary structure. There was no effect of magnesium ion on the far ultraviolet spectrum. Evidently magnesium ion has no effect on the secondary structure. Substrate bound to the enzyme when the above cations were present although calcium permits no enzymatic activity. The CD spectral difference produced by the substrate was nearly the reverse of that produced by the metal ions. Glycolic acid phosphate, a competitive inhibitor lacking carbon-3, produced no effect, indicating carbon-3 was necessary for the CD spectral changes. The CD and visible absorption spectra of nickel and cobalt bound to various sites on the enzyme showed that the binding sites were octahedral or distorted octahedral in coordination and that the ligands appeared to be oxyligands: water molecules, hydroxyl or carboxyl groups. Examination of the effects of substrate and two compounds thought to be "transition state analogues" showed that these perturbed the "conformational" sites of the enzyme. The "catalytic" and "inhibitory" sites did not appear to be very CD active.

Fluid loading to reduce abnormalities of fetal heart rate and maternal hypotension during epidural analgesia in labour

Fetal heart rate (FHR) was recorded and maternal blood pressure measured in 104 patients in whom lumbar epidural analgesia was induced in labour. Fifty-one patients received an intravenous load of 11 of Hartmann's solution immediately before the epidural injection. This infusion significantly reduced the incidence of abnormalities of FHR from 34% to 12% and of maternal hypotension from 28% to 2%. We did not study mothers with pre-eclampsia and hypertension, but we conclude that there is a strong case for preloading all other mothers in whom lumbar epidural analgesia is induced in labour.