Exploring the neurotransmitter labyrinth in nematodes

Nematodes include both free-living species such as Caenorhabditis elegans and major parasites of humans, livestock and plants. The apparent simplicity and uniformity of their nervous system belies a rich diversity of putative signalling molecules,particularly neuropeptides. This new appreciation stems largely from the genome-sequencing project with C. elegans, which is due to be completed by the end of 1998. The project has provided additional insights into other aspects of nematode neurobiology, as have studies on the mechanism of action of anthelmintics. Here, progress on the identification, localization, synthesis and physiological actions of transmitters identified in nematodes is explored.

FMRFamide-related peptides (FaRPs) in nematodes: Occurrence and neuromuscular physiology

The occurrence of classical neurotransmitter molecules and numerous peptidic messenger molecules in nematode nervous systems indicate that although structurally simple, nematode nervous systems are chemically complex. Thus far, studies on one nematode neuropeptide family, namely the FMRFamide-related peptides (FaRPs), have revealed an unexpected variety of neuropeptide structures in both free-living and parasitic species. To date 23 nematode FaRPs have been structurally characterized including 12 from Ascaris suum, 8 from Caenorhabditis elegans, 5 from Panagrellus redivivus and 1 from Haemonchus contortus. Ten FaRP-encoding genes have been identified in Caenorhabditis elegans. However, the full complement of nematode neuronal messengers has yet to be described and unidentified nematode FaRPs await detection. Preliminary characterization of the actions of nematode neuropeptides on the somatic musculature and neurones of A. suum has revealed that these peptidic messengers have potent and complex effects. Identified complexities include the biphasic effects of KNEFIRFamide/KHEYLRFamide (AF1/2; relaxation of tone followed by oscillatory contractile activity) and KPNFIRFamide (PF4; rapid relaxation of tone followed by an increase in tone), the diverse actions of KSAYMRFamide (AF8 or PF3; relaxes dorsal muscles and contracts ventral muscles) and the apparent coupling of the relaxatory effects of SDPNFLRFamide/SADPNFLRFamide (PF1/PF2) to nitric oxide release. Indeed, all of the nematode FaRPs which have been tested on somatic muscle strips of A. suum have actions which are clearly physiologically distinguishable. Although we are a very long way from understanding how the actions of these peptides are co-ordinated, not only with those of each other but also with those of the classical transmitter molecules, to control nematode behaviour, their abundance coupled with their diversity of structure and function indicates a hitherto unidentified sophistication to nematode neuromuscular intergration.

KSAYMRFAMIDE - A NOVEL FMRFAMIDE-RELATED HEPTAPEPTIDE FROM THE FREE-LIVING NEMATODE, PANAGRELLUS-REDIVIVUS, WHICH IS MYOACTIVE IN THE PARASITIC NEMATODE, ASCARIS-SUUM

In nematodes, FMRFamide-related peptides (FaRPs) have been structurally characterised from the parasite, Ascaris suum, and from two free-living species, Panagrellus redivivus and Caenorhabditis elegans. While both FaRPs isolated from P. redivivus (PF1 and PF2) have been identified in C. elegans the two heptapeptides isolated from A. suum (AF1 and AF2) have until recently been considered unique to this parasitic species. We have recently isolated AF2 from P. redivivus and, during this study, an additional novel heptapeptide amide, Lys-Ser-Ala-Tyr-Met-Arg-Phe amide (KSAYMRFamide), was structurally characterised. A synthetic replicate of this peptide induced a rapid concentration-dependent muscle tension increase in an isolated A. suum somatic muscle preparation, with a threshold of approximately 0.1 mu M. These data suggest that the complement of FaRPs in parasitic and free-living nematodes may not be as radically different as preliminary studies would suggest, and that the absence of AF1, AF2 and KSAYMRFamide on the C. elegans FMRFamide-related peptide gene (flp-1) may imply the presence of at least two different FaRP genes in nematodes. (C) 1994 Academic Press, Inc.

A quorum-quenching approach to investigate the conservation of quorum-sensing-regulated functions within the Burkholderia cepacia complex

Taxonomic studies of the past few years have shown that the Burkholderia cepacia complex, a heterogeneous group of B. cepacia-like organisms, consists of at least nine species. B. cepacia complex strains are ubiquitously distributed in nature and have been used for biocontrol, bioremediation, and plant growth promotion purposes. At the same time, B. cepacia complex strains have emerged as important opportunistic pathogens of humans, particularly those with cystic fibrosis. All B. cepacia complex species investigated thus far use quorum-sensing (QS) systems that rely on N-acylhomoserine lactone (AHL) signal molecules to express certain functions, including the production of extracellular proteases, swarming motility, biofilm formation, and pathogenicity, in a population-density-dependent manner. In this study we constructed a broad-host-range plasmid that allowed the heterologous expression of the Bacillus sp. strain 240B1 AiiA lactonase, which hydrolyzes the lactone ring of various AHL signal molecules, in all described B. cepacia complex species. We show that expression of AiiA abolished or greatly reduced the accumulation of AHL molecules in the culture supernatants of all tested B. cepacia complex strains. Phenotypic characterization of wild-type and transgenic strains revealed that protease production, swarming motility, biofilm formation, and Caenorhabditis elegans killing efficiency was regulated by AHL in the large majority of strains investigated.

Progress, challenges and perspectives in positron physics:Report on the XIIth international positron workshop

A report is presented of the XIIth International Workshop on Positron and Positronium Physics (Sandbjerg, Denmark, 19-21 July 2003). This workshop covered positron and positronium interactions with atoms, molecules and condensed matter systems. One key development reported was the first creation in the laboratory of low-energy antihydrogen atoms. Facets of positron-electron many-body systems were also considered, including the positronium molecule and BEC gases of positronium atoms. Aspects of the future of the field were discussed, including the development of new theoretical and experimental capabilities.

Scattering theory of multilevel atoms interacting with arbitrary radiation fields

We present a generic transfer matrix approach for the description of the interaction of atoms possessing multiple ground state and excited state sublevels with light fields. This model allows us to treat multi-level atoms as classical scatterers in light fields modified by, in principle, arbitrarily complex optical components such as mirrors, resonators, dispersive or dichroic elements, or filters. We verify our formalism for two prototypical sub-Doppler cooling mechanisms and show that it agrees with the standard literature.

Robust non-Markovianity in ultracold gases

We study the effect of thermal fluctuations on a probe qubit interacting with a Bose–Einstein condensed (BEC) reservoir. The zero-temperature case was studied in our previous work (Haikka et al 2011 Phys. Rev. A 84 031602), where we proposed a method for probing the effects of dimensionality and scattering length of a BEC based on its behavior as an environment. In this paper, we show that the sensitivity of the probe qubit is remarkably robust against thermal noise. We give an intuitive explanation for the thermal resilience, showing that it is due to the unique choice of the probe qubit architecture of our model.

GHMP Kinases - Structures, Mechanisms and Potential for Therapeutically Relevant Inhibition

The GHMP kinases are a structurally related family of small molecule kinases named after four of its members - galactokinase, homoserine kinase, mevalonate kinase and phosphomevalonate kinase. The group also includes the enzymes N-acetylgalactosamine kinase, arabinose kinase, mevalonate 5-diphosphate decarboxylase, archeal shikimate kinase and 4-(cytidine 5'-diphospho)-2-c-methyl-D-erythritol kinase. In addition the group includes two members not known to be catalytically active, the Caenorhabditis elegans sex-fate determining protein XOL-1 and the Saccharomyces cerevisiae transcriptional activator Gal3p. Two catalytic mechanisms have been proposed for GHMP kinases. The structure of mevalonate kinase suggests that an aspartate residue acts as an active site base, removing a proton from the substrate to facilitate attack on the ? phosphate of MgATP. In contrast, in homoserine kinase there is no potential catalytic base and it is proposed that catalysis is driven by transition state stabilisation. Potential chemotherapeutic interventions against GHMP kinases fall into three main categories: inhibition of galactokinase to assist suffers of galactosemia, inhibition of mevalonate kinase or mevalonate 5-diphosphate decarboxylase to reduce flux through the cholesterol biosynthesis pathway and inhibition of bacterial GHMP kinases for novel anti-microbial therapies. These are in the early stages of development, but the accumulation of structural and mechanistic data will assist future progress.

When Casimir meets Kibble-Zurek

Verification of the dynamical Casimir effect (DCE) in optical systems is still elusive due to the very demanding requirements for its experimental implementation. This typically requires very fast changes in the boundary conditions of the problem. We show that an ensemble of two-level atoms collectively coupled to the electromagnetic field of a cavity, driven at low frequencies and close to a quantum phase transition, stimulates the production of photons from the vacuum. This paves the way for an effective simulation of the DCE through a mechanism that has recently found experimental demonstration. The spectral properties of the emitted radiation reflect the critical nature of the system and allow us to link the detection of DCE to the Kibble-Zurek mechanism for the production of defects when crossing a continuous phase transition.

Historical data reveal power-law dispersal patterns of invasive aquatic species

Understanding how invasive species spread is of particular concern in the current era of globalisation and rapid environmental change. The occurrence of super-diffusive movements within the context of Lévy flights has been discussed with respect to particle physics, human movements, microzooplankton, disease spread in global epidemiology and animal foraging behaviour. Super-diffusive movements provide a theoretical explanation for the rapid spread of organisms and disease, but their applicability to empirical data on the historic spread of organisms has rarely been tested. This study focuses on the role of long-distance dispersal in the invasion dynamics of aquatic invasive species across three contrasting areas and spatial scales: open ocean (north-east Atlantic), enclosed sea (Mediterranean) and an island environment (Ireland). Study species included five freshwater plant species, Azolla filiculoides, Elodea canadensis, Lagarosiphon major, Elodea nuttallii and Lemna minuta; and ten species of marine algae, Asparagopsis armata, Antithamnionella elegans, Antithamnionella ternifolia, Codium fragile, Colpomenia peregrina, Caulerpa taxifolia, Dasysiphonia sp., Sargassum muticum, Undaria pinnatifida and Womersleyella setacea. A simulation model is constructed to show the validity of using historical data to reconstruct dispersal kernels. Lévy movement patterns similar to those previously observed in humans and wild animals are evident in the re-constructed dispersal pattern of invasive aquatic species. Such patterns may be widespread among invasive species and could be exacerbated by further development of trade networks, human travel and environmental change. These findings have implications for our ability to predict and manage future invasions, and improve our understanding of the potential for spread of organisms including infectious diseases, plant pests and genetically modified organisms.