Space-Time Structured Plasma Waves.

Electrostatic waves play a critical role in nearly every branch of plasma physics from fusion to advanced accelerators, to astro, solar, and ionospheric physics. The properties of planar electrostatic waves are fully determined by the plasma conditions, such as density, temperature, ionization state, or details of the distribution functions. Here we demonstrate that electrostatic wave packets structured with space-time correlations can have properties that are independent of the plasma conditions. For instance, an appropriately structured electrostatic wave packet can travel at any group velocity, even backward with respect to its phase fronts, while maintaining a localized energy density. These linear, propagation-invariant wave packets can be constructed with or without orbital angular momentum by superposing natural modes of the plasma and can be ponderomotively excited by space-time structured laser pulses like the flying focus.

Programmable-trajectory ultrafast flying focus pulses.

"Flying focus" techniques produce laser pulses with dynamic focal points that travel distances much greater than a Rayleigh length. The implementation of these techniques in laser-based applications requires the design of optical configurations that can both extend the focal range and structure the radial group delay. This article describes a method for designing optical configurations that produce ultrashort flying focus pulses with programmable-trajectory focal points. The method is illustrated by several examples that employ an axiparabola for extending the focal range and either a reflective echelon or a deformable mirror-spatial light modulator pair for structuring the radial group delay. The latter configuration enables rapid exploration and optimization of flying foci, which could be ideal for experiments.

Microcoulomb (0.7 ± [Formula: see text] µC) laser plasma accelerator on OMEGA EP.

Laser-plasma accelerators (LPAs) driven by picosecond-scale, kilojoule-class lasers can generate particle beams and x-ray sources that could be utilized in experiments driven by multi-kilojoule, high-energy-density science (HEDS) drivers such as the OMEGA laser at the Laboratory for Laser Energetics (LLE) or the National Ignition Facility at Lawrence Livermore National Laboratory. This paper reports on the development of the first LPA driven by a short-pulse, kilojoule-class laser (OMEGA EP) connected to a multi-kilojoule HEDS driver (OMEGA). In experiments, electron beams were produced with electron energies greater than 200 MeV, divergences as low as 32 mrad, charge greater than 700 nC, and conversion efficiencies from laser energy to electron energy up to 11%. The electron beam charge scales with both the normalized vector potential and plasma density. These electron beams show promise as a method to generate MeV-class radiography sources and improved-flux broadband x-ray sources at HEDS drivers.

Intestinal smooth muscle phenotype determines enteric neuronal survival via GDNF expression.

Intestinal inflammation causes initial axonal degeneration and neuronal death, as well as the proliferation of intestinal smooth muscle cells (ISMC), but subsequent axonal outgrowth leads to re-innervation. We recently showed that expression of glial cell-derived neurotrophic factor (GDNF), the critical neurotrophin for the post-natal enteric nervous system (ENS) is upregulated in ISMC by inflammatory cytokines, leading us to explore the relationship between ISMC growth and GDNF expression. In co-cultures of myenteric neurons and ISMC, GDNF or fetal calf serum (FCS) was equally effective in supporting neuronal survival, with neurons forming extensive axonal networks among the ISMC. However, only GDNF was effective in low-density cultures where neurons lacked contact with ISMC. In early-passage cultures of colonic circular smooth muscle cells (CSMC), polymerase chain reaction (PCR) and western blotting showed that proliferation was associated with expression of GDNF, and the successful survival of neonatal neurons co-cultured on CSMC was blocked by vandetanib or siGDNF. In tri-nitrobenzene sulfonic acid (TNBS)-induced colitis, immunocytochemistry showed the selective expression of GDNF in proliferating CSMC, suggesting that smooth muscle proliferation supports the ENS in vivo as well as in vitro. However, high-passage CSMC expressed significantly less GDNF and failed to support neuronal survival, while expressing reduced amounts of smooth muscle marker proteins. We conclude that in the inflamed intestine, smooth muscle proliferation supports the ENS, and thus its own re-innervation, by expression of GDNF. In chronic inflammation, a compromised smooth muscle phenotype may lead to progressive neural damage. Intestinal stricture formation in human disease, such as inflammatory bowel disease (IBD), may be an endpoint of failure of this homeostatic mechanism.

Early inflammatory damage to intestinal neurons occurs via inducible nitric oxide synthase.

Intestinal inflammation affects the enteric nervous system (ENS) that lies adjacent to the smooth muscle layers. Previously, we showed that the loss of ENS neurons in animal models such as tri-nitrobenzene sulphonic acid (TNBS)-induced colitis was a limited and early event despite progressive worsening of inflammation. Here, we demonstrated that the rapid appearance of activated immune cells in the intestinal wall is selectively neurotoxic via iNOS-derived NO, using TNBS-induced colitis in both rats and mice, and a co-culture model of ENS neurons and smooth muscle. An influx of neutrophils and macrophages occurred within hours of initiation of rat colitis, correlating with iNOS expression, acutely elevated NO and neuronal death. In vitro, chemical donors of NO selectively caused axonal damage and neuronal death. These outcomes were similar to those seen with combined culture with either activated peritoneal immune cells or the immune cell lines RAW-264 and RBL-2H3. Immune cell-mediated neurotoxicity was blocked by the iNOS inhibitor L-NIL, and neuronal death was inhibited by the RIP-1 kinase inhibitor necrostatin. In a mouse model, the stereotypic loss of myenteric neurons by Day 4 post-TNBS was abrogated by the selective iNOS inhibitors L-NIL or 1400W without effect on other parameters of intestinal inflammation. Preservation of ENS neurons also ameliorated the hyperplasia of smooth muscle that is characteristic of intestinal inflammation, in line with prior work showing neural regulation of smooth muscle phenotype. This identifies a predominant pathway of immune cell damage to the ENS, where early, acute elevation of NO from iNOS can be cytotoxic to myenteric neurons.

Deep drilling into the Chesapeake Bay impact structure.

Samples from a 1.76-kilometer-deep corehole drilled near the center of the late Eocene Chesapeake Bay impact structure (Virginia, USA) reveal its geologic, hydrologic, and biologic history. We conducted stratigraphic and petrologic analyses of the cores to elucidate the timing and results of impact-melt creation and distribution, transient-cavity collapse, and ocean-water resurge. Comparison of post-impact sedimentary sequences inside and outside the structure indicates that compaction of the crater fill influenced long-term sedimentation patterns in the mid-Atlantic region. Salty connate water of the target remains in the crater fill today, where it poses a potential threat to the regional groundwater resource. Observed depth variations in microbial abundance indicate a complex history of impact-related thermal sterilization and habitat modification, and subsequent post-impact repopulation.

HIV serodiscordant sex partners and the prevalence of human herpesvirus 8 infection among HIV negative men who have sex with men: baseline data from the EXPLORE Study.

OBJECTIVES: Human herpesvirus 8 (HHV-8) infection is common among men who have sex with men (MSM), especially those infected with HIV, and is frequently detected in saliva. We sought to determine whether oral or anogenital contact with HIV discordant, or unknown serostatus sexual partners is associated with HHV-8 seroprevalence among HIV negative MSM. METHODS: HIV negative MSM participating in a behavioural intervention trial for the prevention of HIV infection (the EXPLORE study) were recruited from the Seattle and Denver areas for participation in this cross sectional study. Participants completed detailed questionnaires regarding sexual behaviour, focusing on activities with possible exposure to the oropharynx. Serum samples from study enrollment were tested for the presence of HHV-8 antibodies using whole virus enzyme immunoassay and immunofluorescence assay to latent and lytic proteins. RESULTS: 198/819 MSM (24.3%) were HHV-8 antibody positive. Exposure to saliva with HIV positive and HIV unknown serostatus sex partners was reported by 83% and 90% of all men, respectively. In a multivariate model, reporting more than the median number of lifetime sex partners (OR 2.2, p = 0.03) or lifetime sex partners of unknown HIV status (OR 1.7, p = 0.03), and the performance of oro-anal sex ("rimming") on partners whose HIV status is unknown (OR 2.7, p = 0.04) were independently associated with HHV-8 infection. CONCLUSIONS: The oropharynx may be an important anatomical site in HHV-8 acquisition, and contact with HIV serodiscordant or unknown sex partners is associated with higher HHV-8 seroprevalence among HIV negative MSM.

A role for RIC-8 (Synembryn) and GOA-1 (G(o)alpha) in regulating a subset of centrosome movements during early embryogenesis in Caenorhabditis elegans.

RIC-8 (synembryn) and GOA-1 (G(o)alpha) are key components of a signaling network that regulates neurotransmitter secretion in Caenorhabditis elegans. Here we show that ric-8 and goa-1 reduction of function mutants exhibit partial embryonic lethality. Through Nomarski analysis we show that goa-1 and ric-8 mutant embryos exhibit defects in multiple events that involve centrosomes, including one-cell posterior centrosome rocking, P(1) centrosome flattening, mitotic spindle alignment, and nuclear migration. In ric-8 reduction of function backgrounds, the embryonic lethality, spindle misalignments and delayed nuclear migration are strongly enhanced by a 50% reduction in maternal goa-1 gene dosage. Several other microfilament- and microtubule-mediated events, as well as overall embryonic polarity, appear unperturbed in the mutants. In addition, our results suggest that RIC-8 and GOA-1 do not have roles in centrosome replication, in the diametric movements of daughter centrosomes along the nuclear membrane, or in the extension of microtubules from centrosomes. Through immunostaining we show that GOA-1 (G(o)alpha) localizes to cell cortices as well as near centrosomes. Our results demonstrate that two components of a neuronal signal transduction pathway also play a role in centrosome movements during early embryogenesis.

RIC-8 (Synembryn): a novel conserved protein that is required for G(q)alpha signaling in the C. elegans nervous system.

Recent studies describe a network of signaling proteins centered around G(o)alpha and G(q)alpha that regulates neurotransmitter secretion in C. elegans by controlling the production and consumption of diacylglycerol (DAG). We sought other components of the Goalpha-G(q)alpha signaling network by screening for aldicarb-resistant mutants with phenotypes similar to egl-30 (G(q)alpha) mutants. In so doing, we identified ric-8, which encodes a novel protein named RIC-8 (synembryn). Through cDNA analysis, we show that RIC-8 is conserved in vertebrates. Through immunostaining, we show that RIC-8 is concentrated in the cytoplasm of neurons. Exogenous application of phorbol esters or loss of DGK-1 (diacylglycerol kinase) rescues ric-8 mutant phenotypes. A genetic analysis suggests that RIC-8 functions upstream of, or in conjunction with, EGL-30 (G(q)alpha).

Class VI unconventional myosin is required for spermatogenesis in Drosophila.

We have identified partial loss of function mutations in class VI unconventional myosin, 95F myosin, which results in male sterility. During spermatogenesis the germ line precursor cells undergo mitosis and meiosis to form a bundle of 64 spermatids. The spermatids remain interconnected by cytoplasmic bridges until individualization. The process of individualization involves the formation of a complex of cytoskeletal proteins and membrane, the individualization complex (IC), around the spermatid nuclei. This complex traverses the length of each spermatid resolving the shared membrane into a single membrane enclosing each spermatid. We have determined that 95F myosin is a component of the IC whose function is essential for individualization. In wild-type testes, 95F myosin localizes to the leading edge of the IC. Two independent mutations in 95F myosin reduce the amount of 95F myosin in only a subset of tissues, including the testes. This reduction of 95F myosin causes male sterility as a result of defects in spermatid individualization. Germ line transformation with the 95F myosin heavy chain cDNA rescues the male sterility phenotype. IC movement is aberrant in these 95F myosin mutants, indicating a critical role for 95F myosin in IC movement. This report is the first identification of a component of the IC other than actin. We propose that 95F myosin is a motor that participates in membrane reorganization during individualization.

Goalpha and diacylglycerol kinase negatively regulate the Gqalpha pathway in C. elegans.

We investigated the EGL-30 (Gqalpha) pathway in C. elegans by using genetic screens to identify genes that confer phenotypes similar to egl-30 mutants. One such gene, egl-8, encodes a phospholipase Cbeta that is present throughout the nervous system and near intestinal cell junctions. EGL-30 and EGL-8 appear to positively regulate synaptic transmission because reducing their function results in strong aldicarb resistance and slow locomotion rates. In contrast, GOA-1 (Goalpha) and DGK-1 (diacylglycerol kinase) appear to negatively regulate synaptic transmission, because reducing their function results in strong aldicarb hypersensitivity and hyperactive locomotion. A genetic analysis suggests that GOA-1 negatively regulates the EGL-30 pathway and that DGK-1 antagonizes the EGL-30 pathway.

The actin cytoskeleton is required for maintenance of posterior pole plasm components in the Drosophila embryo.

Localization of mRNAs is one of many aspects of cellular organization that requires the cytoskeleton. In Drosophila, microtubules are known to be required for correct localization of developmentally important mRNAs and proteins during oogenesis; however, the role of the actin cytoskeleton in localization is less clear. Furthermore, it is not known whether either of these cytoskeletal systems are necessary for maintenance of RNA localization in the early embryo. We have examined the contribution of the actin and microtubule cytoskeletons to maintenance of RNA and protein localization in the early Drosophila embryo. We have found that while microtubules are not necessary, the actin cytoskeleton is needed for stable association of nanos, oskar, germ cell-less and cyclin B mRNAs and Oskar and Vasa proteins at the posterior pole in the early embryo. In contrast, bicoid RNA, which is located at the anterior pole, does not require either cytoskeletal system to remain at the anterior.

A class VI unconventional myosin is associated with a homologue of a microtubule-binding protein, cytoplasmic linker protein-170, in neurons and at the posterior pole of Drosophila embryos.

Coordination of cellular organization requires the interaction of the cytoskeletal filament systems. Recently, several lines of investigation have suggested that transport of cellular components along both microtubules and actin filaments is important for cellular organization and function. We report here on molecules that may mediate coordination between the actin and microtubule cytoskeletons. We have identified a 195-kD protein that coimmunoprecipitates with a class VI myosin, Drosophila 95F unconventional myosin. Cloning and sequencing of the gene encoding the 195-kD protein reveals that it is the first homologue identified of cytoplasmic linker protein (CLIP)-170, a protein that links endocytic vesicles to microtubules. We have named this protein D-CLIP-190 (the predicted molecular mass is 189 kD) based on its similarity to CLIP-170 and its ability to cosediment with microtubules. The similarity between D-CLIP-190 and CLIP-170 extends throughout the length of the proteins, and they have a number of predicted sequence and structural features in common. 95F myosin and D-CLIP-190 are coexpressed in a number of tissues during embryogenesis in Drosophila. In the axonal processes of neurons, they are colocalized in the same particulate structures, which resemble vesicles. They are also colocalized at the posterior pole of the early embryo, and this localization is dependent on the actin cytoskeleton. The association of a myosin and a homologue of a microtubule-binding protein in the nervous system and at the posterior pole, where both microtubule and actin-dependent processes are known to be important, leads us to speculate that these two proteins may functionally link the actin and microtubule cytoskeletons.

A genetic selection for Caenorhabditis elegans synaptic transmission mutants.

We have isolated 165 Caenorhabditis elegans mutants, representing 21 genes, that are resistant to inhibitors of cholinesterase (Ric mutants). Since mutations in 20 of the genes appear not to affect acetylcholine reception, we suggest that reduced acetylcholine release contributes to the Ric phenotype of most Ric mutants. Mutations in 15 of the genes lead to defects in a gamma-aminobutyric acid-dependent behavior; these genes are likely to encode proteins with general, rather than cholinergic-specific, roles in synaptic transmission. Ten of the genes have been cloned. Seven encode homologs of proteins that function in the synaptic vesicle cycle: two encode cholinergic-specific proteins, while five encode general presynaptic proteins. Two other Ric genes encode homologs of G-protein signaling molecules. Our assessment of synaptic function in Ric mutants, combined with the homologies of some Ric mutants to presynaptic proteins, suggests that the analysis of Ric genes will continue to yield insights into the regulation and functioning of synapses.

Actin organization, bristle morphology, and viability are affected by actin capping protein mutations in Drosophila.

Regulation of actin filament length and orientation is important in many actin-based cellular processes. This regulation is postulated to occur through the action of actin-binding proteins. Many actin-binding proteins that modify actin in vitro have been identified, but in many cases, it is not known if this activity is physiologically relevant. Capping protein (CP) is an actin-binding protein that has been demonstrated to control filament length in vitro by binding to the barbed ends and preventing the addition or loss of actin monomers. To examine the in vivo role of CP, we have performed a molecular and genetic characterization of the beta subunit of capping protein from Drosophila melanogaster. We have identified mutations in the Drosophila beta subunit-these are the first CP mutations in a multicellular organism, and unlike CP mutations in yeast, they are lethal, causing death during the early larval stage. Adult files that are heterozygous for a pair of weak alleles have a defect in bristle morphology that is correlated to disorganized actin bundles in developing bristles. Our data demonstrate that CP has an essential function during development, and further suggest that CP is required to regulate actin assembly during the development of specialized structures that depend on actin for their morphology.

The LYS5 gene of Saccharomyces cerevisiae.

The LYS2 and LYS5 genes of Saccharomyces cerevisiae together encode the 180-kDa alpha-aminoadipate reductase (AAR) in the biosynthetic pathway of lysine. The 4.8-kb LYS2 gene encodes the 155-kDa subunit of AAR. The complete nucleotide (nt) sequence of the 1.1-kb LYS5 gene is presented in this report. It contains a single continuous open reading frame of 816 nt encoding a 272-amino-acid, 30.6-kDa polypeptide.

The 95F unconventional myosin is required for proper organization of the Drosophila syncytial blastoderm.

The 95F myosin, a class VI unconventional myosin, associates with particles in the cytoplasm of the Drosophila syncytial blastoderm and is required for the ATP- and F-actin-dependent translocation of these particles. The particles undergo a cell cycle-dependent redistribution from domains that surround each nucleus in interphase to transient membrane invaginations that provide a barrier between adjacent spindles during mitosis. When 95F myosin function is inhibited by antibody injection, profound defects in syncytial blastoderm organization occur. This disorganization is seen as aberrant nuclear morphology and position and is suggestive of failures in cytoskeletal function. Nuclear defects correlate with gross defects in the actin cytoskeleton, including indistinct actin caps and furrows, missing actin structures, abnormal spacing of caps, and abnormally spaced furrows. Three-dimensional examination of embryos injected with anti-95F myosin antibody reveals that actin furrows do not invaginate as deeply into the embryo as do normal furrows. These furrows do not separate adjacent mitoses, since microtubules cross over them. These inappropriate microtubule interactions lead to aberrant nuclear divisions and to the nuclear defects observed. We propose that 95F myosin function is required to generate normal actin-based transient membrane furrows. The motor activity of 95F myosin itself and/or components within the particles transported to the furrows by 95F myosin may be required for normal furrows to form.