Lockery S (2010) Neuronal Development, Synaptic Function and Behavior, Madison, WI "A stochastic model of command neuron function"

Lockery S

[Neuronal Development, Synaptic Function and Behavior, Madison, WI, 2010]

Locomotory state in C. elegans is regulated by a network of forward and reverse command neurons in two reciprocally connected pools, but how this network functions is poorly understood. We propose a model in which the network acts as a stochastic system. The model is based on three assumptions: (i) Forward neurons act as a single unit F and reverse neurons act as a single unit R. (ii) Unit activation switches stochastically between two activation states: 0 and 1, corresponding to off and on, respectively. (iii) The rate of a 0-1 transition, written a01, is a monotonic increasing function of synaptic input, i.e. the weighted sum of presynaptic activation states. Given two neurons and two activation states, there are four possible states of the network (F,R) = {(0,0), (0,1), (1,0), (1,1)}. Previous neuronal ablations suggest that the first three states correspond, respectively, to locomotory pauses, forward locomotion, and reverse locomotion; we propose that the state (1,1) also corresponds to pauses. The kinetics of the network are fully described by eight rate constants. Using a maximum likelihood procedure, these quantities can be estimated from empirically determined probability density functions for three behavioral states (Forward, Reverse, and Pause) together with the time series of velocities recorded for individual worms. Synaptic interactions in the model are described by six coefficients: the two cross connections (WFR, WRF), the two self-connections (WFF, WRR), and the two connections representing sensory input (hR, hF). Assuming that the forward and reverse motor systems can be approximated as semi-linear Hopfield neurons, the synaptic coefficients can be estimated from the rate constants. The resulting model recapitulates a wide range of C. elegans behaviors. For example, both the touch-induced escape response and the gradual transition from local search to ranging behavior can be modeled by making hR and hF functions of time, whereas chemotaxis can be modeled by making the hR and hF functions of the local chemical gradient. We conclude that the stochastic switch model provides an intuitive yet predictive representation of command neuron function.

Goodman MB et al. (1998) East Coast Worm Meeting "In situ patch-clamp recording from neurons in C. elegans"

Goodman MB, Chalfie M

[East Coast Worm Meeting, 1998]

We have extended recently described methods for in situ patch-clamp recording from C. elegans neurons (1, 2) to permit recording in adult animals. The main improvement is the use of a fixed-stage, upright microscope mounted on an x-y translation stage. In this way, worms can be visualized from above using a high N.A. water immersion objective (Zeiss 63X/0.9 or 100X/1.0). This arrangement gives superior optics compared to viewing worms on an inverted microscope and makes it possible to expose neurons in adult animals. In addition, methods for exposing neuronal cell bodies in the head were modified to expose neuronal cell bodies in the tail for in situ patch-clamp recording. With this apparatus, we plan to record the response of PLM cells to light touch. 1. Lockery, S. R. & Goodman, M. B. (1998) Tight-seal whole-cell patch clamping of C. elegans neurons. Methods in Enzymology (in press). 2. Goodman, M. B., Hall, D. H., Avery, L. & Lockery, S. R. (1998). Active currents regulate sensitivity and dynamic range in C. elegans neurons. Neuron (in press).

Vinci CR et al. (2007) J Biol Chem "Recognition of age-damaged (R,S)-adenosyl-L-methionine by two methyltransferases in the yeast Saccharomyces cerevisiae."

Vinci CR, Clarke SG

[J Biol Chem, 2007]

The biological methyl donor, S adenosylmethionine (AdoMet), can exist in two diastereoisomeric states with respect to its sulfonium ion. The "S" configuration, (S,S)AdoMet, is the only form that is produced enzymatically as well as the only form used in almost all biological methylation reactions. Under physiological conditions, however, the sulfonium ion can spontaneously racemize to the "R" form, producing (R,S)AdoMet. As of yet, (R,S)AdoMet has no known physiological function and may inhibit cellular reactions. In this study, two enzymes have been found in Saccharomyces cerevisiae that are capable of recognizing (R,S)AdoMet and using it to methylate homocysteine to form methionine. These enzymes are the products of the SAM4 and MHT1 genes, previously identified as homocysteine methyltransferases dependent upon AdoMet and S-methylmethionine respectively. We find here that Sam4 recognizes both (S,S) and (R,S)AdoMet, but its activity is much higher with the R,S form. Mht1 reacts with only the R,S form of AdoMet while no activity is seen with the S,S form. R,S-specific homocysteine methyltransferase activity is also shown here to occur in extracts of Arabidopsis thaliana, Drosophila melanogaster, and Caenorhabditis elegans, but has not been detected in several tissue extracts of Mus musculus. Such activity may function to prevent the accumulation of (R,S)AdoMet in these organisms.

Ferree TC et al. (1997) International C. elegans Meeting "Mathematical analysis of neural networks for chemotaxis in C. elegans"

Lockery SR, Ferree TC

[International C. elegans Meeting, 1997]

C. elegans moves up a gradient of chemical attractant (chemotaxis) using chemosensory neurons at the tip of the nose. Laser ablations[1,2] and anatomical data[3] indicate that chemosensory information is processed by a highly interconnected neural network of sensory neurons, interneurons and motor neurons. Patch-clamp recordings from neurons in the nerve ring show that graded potentials, rather than action potentials, are the main kind of electrical signal[4]. To determine how a network of graded-potential neurons steers worms up gradients, we constructed an idealized model chemotaxis network of linear neurons (the simplest kind of graded-potential neurons), which controls the behavior of a simulated worm. Analyzing the model network using linear systems theory, we found that the model produced chemotaxis by altering neck angle, and thus rate of turning R, as a function of chemosensory input, according to the equation R = k1 + k2 C + k3 dC/dt, where k1, k2 and k3 are constants, and C is the chemical concentration at the tip of the nose. Thus, the model predicts that in real worms, chemotaxis may be controlled by turning in response to absolute concentration and its time derivative. We are testing this prediction by tracking worms in measured concentration gradients. We are also testing the robustness of the model network by asking whether it can control taxis behavior in a freely moving robot. 1. Bargmann, C., and H. R. Horvitz (1991). Neuron 7:729-742. 2. Bargmann, C., unpublished. 3. White, J. G., E. Southgate, J. N. Thompson and S. Brenner (1986). Phil. Trans. R. Soc. London 314: 1-340. 4. Lockery, S. R., and M. B. Goodman, unpublished.

Fanning S et al. (2018) Mol Cell "Lipidomic Analysis of -Synuclein Neurotoxicity Identifies Stearoyl CoA Desaturase as a Target for Parkinson Treatment."

Lou Y, Haque A, Freyzon Y, Farese RV, Terry-Kantor E, Hofbauer HF, Termine D, Welte MA, Barrasa MI, Imberdis T, Noble T, Lindquist S, Clish CB, Jaenisch R, Pincus D, Nuber S, Sandoe J, Kohlwein SD, Kim TE, Ho GPH, Ramalingam N, Walther TC, Baru V, Selkoe D, Srinivasan S, Landgraf D, Soldner F, Dettmer U, Fanning S, Becuwe M, Newby G

[Mol Cell, 2018]

In Parkinson's disease (PD), -synuclein (S) pathologically impacts the brain, a highly lipid-rich organ. We investigated how alterations in S or lipid/fattyacid homeostasis affect each other. Lipidomic profiling of human S-expressing yeast revealed increases in oleic acid (OA, 18:1), diglycerides, and triglycerides. These findings were recapitulated in rodent and human neuronal models of S dyshomeostasis (overexpression; patient-derived triplication or E46K mutation; E46K mice). Preventing lipid droplet formation or augmenting OA increased S yeast toxicity; suppressing the OA-generating enzyme stearoyl-CoA-desaturase (SCD) was protective. Genetic or pharmacological SCD inhibition ameliorated toxicity in S-overexpressing rat neurons. In a C.elegans model, SCD knockout prevented S-induced dopaminergic degeneration. Conversely, we observed detrimental effects of OA on S homeostasis: in human neural cells, excess OA caused S inclusion formation, which was reversed by SCD inhibition. Thus, monounsaturated fatty acid metabolism is pivotal for S-induced neurotoxicity, and inhibiting SCD represents a novel PD therapeutic approach.

Faumont S et al. (2012) Curr Opin Neurobiol "Neuronal microcircuits for decision making in C. elegans."

Lindsay T, Lockery S, Faumont S

[Curr Opin Neurobiol, 2012]

The simplicity and genetic tractability of the nervous system of the nematode Caenorhabditis elegans make it an attractive system in which to seek biological mechanisms of decision making. Although work in this area remains at an early stage, four basic types paradigms of behavioral choice, a simple form of decision making, have now been demonstrated in C. elegans. A recent series of pioneering studies, combining genetics and molecular biology with new techniques such as microfluidics and calcium imaging in freely moving animals, has begun to elucidate the neuronal mechanisms underlying behavioral choice. The new research has focussed on choice behaviors in the context of habitat and resource localization, for which the neuronal circuit has been identified. Three main circuit motifs for behavioral choice have been identified. One motif is based mainly on changes in the strength of synaptic connections whereas the other two motifs are based on changes in the basal activity of an interneuron and the sensory neuron to which it is electrically coupled. Peptide signaling seems to play a prominent role in all three motifs, and it may be a general rule that concentrations of various peptides encode the internal states that influence behavioral decisions in C. elegans.

Vandecandelaere I et al. (2017) PLoS One "Metabolic activity, urease production, antibiotic resistance and virulence in dual species biofilms of Staphylococcus epidermidis and Staphylococcus aureus."

Deforce D, Coenye T, Van Nieuwerburgh F, Vandecandelaere I

[PLoS One, 2017]

In this paper, the metabolic activity in single and dual species biofilms of Staphylococcus epidermidis and Staphylococcus aureus isolates was investigated. Our results demonstrated that there was less metabolic activity in dual species biofilms compared to S. aureus biofilms. However, this was not observed if S. aureus and S. epidermidis were obtained from the same sample. The largest effect on metabolic activity was observed in biofilms of S. aureus Mu50 and S. epidermidis ET-024. A transcriptomic analysis of these dual species biofilms showed that urease genes and genes encoding proteins involved in metabolism were downregulated in comparison to monospecies biofilms. These results were subsequently confirmed by phenotypic assays. As metabolic activity is related to acid production, the pH in dual species biofilms was slightly higher compared to S. aureus Mu50 biofilms. Our results showed that S. epidermidis ET-024 in dual species biofilms inhibits metabolic activity of S. aureus Mu50, leading to less acid production. As a consequence, less urease activity is required to compensate for low pH. Importantly, this effect was biofilm-specific. Also S. aureus Mu50 genes encoding virulence-associated proteins (Spa, SplF and Dps) were upregulated in dual species biofilms compared to monospecies biofilms and using Caenorhabditis elegans infection assays, we demonstrated that more nematodes survived when co-infected with S. epidermidis ET-024 and S. aureus mutants lacking functional spa, splF or dps genes, compared to nematodes infected with S. epidermidis ET-024 and wild- type S. aureus. Finally, S. epidermidis ET-024 genes encoding resistance to oxacillin, erythromycin and tobramycin were upregulated in dual species biofilms and increased resistance was subsequently confirmed. Our data indicate that both species in dual species biofilms of S. epidermidis and S. aureus influence each other's behavior, but additional studies are required necessary to elucidate the exact mechanism(s) involved.

Vandecandelaere I et al. (2014) Pathog Dis "Protease production by Staphylococcus epidermidis and its effect on Staphylococcus aureus biofilms."

Coenye T, Vandecandelaere I, Depuydt P, Nelis HJ

[Pathog Dis, 2014]

Due to the resistance of Staphylococcus aureus to several antibiotics, treatment of S. aureus infections is often difficult. As an alternative to conventional antibiotics, the field of bacterial interference is investigated. Staphylococcus epidermidis produces a serine protease (Esp) which inhibits S. aureus biofilm formation and which degrades S. aureus biofilms. In this study, we investigated the protease production of 114 S. epidermidis isolates, obtained from biofilms on endotracheal tubes (ET). Most of the S. epidermidis isolates secreted a mixture of serine, cysteine and metalloproteases. We found a link between high protease production by S. epidermidis and the absence of S. aureus in ET biofilms obtained from the same patient. Treating S. aureus biofilms with the supernatant (SN) of the most active protease producing S. epidermidis isolates resulted in a significant biomass decrease compared to untreated controls, while the number of metabolically active cells was not affected. The effect on the biofilm biomass was mainly due to serine proteases. Staphylococcus aureus biofilms treated with the SN of protease producing S. epidermidis were thinner with almost no extracellular matrix. An increased survival of Caenorhabditis elegans, infected with S. aureus Mu50, was observed when the SN of protease positive S. epidermidis was added.

Kamp F et al. (2010) EMBO J "Inhibition of mitochondrial fusion by -synuclein is rescued by PINK1, Parkin and DJ-1."

Haass C, Hegermann J, Giese A, Eimer S, Kamp F, Lutz AK, Nuscher B, Wender N, Brunner B, Winklhofer KF, Exner N, Beyer K, Bartels T

[EMBO J, 2010]

Aggregation of -synuclein (S) is involved in the pathogenesis of Parkinson's disease (PD) and a variety of related neurodegenerative disorders. The physiological function of S is largely unknown. We demonstrate with in vitro vesicle fusion experiments that S has an inhibitory function on membrane fusion. Upon increased expression in cultured cells and in Caenorhabditis elegans, S binds to mitochondria and leads to mitochondrial fragmentation. In C. elegans age-dependent fragmentation of mitochondria is enhanced and shifted to an earlier time point upon expression of exogenous S. In contrast, siRNA-mediated downregulation of S results in elongated mitochondria in cell culture. S can act independently of mitochondrial fusion and fission proteins in shifting the dynamic morphologic equilibrium of mitochondria towards reduced fusion. Upon cellular fusion, S prevents fusion of differently labelled mitochondrial populations. Thus, S inhibits fusion due to its unique membrane interaction. Finally, mitochondrial fragmentation induced by expression of S is rescued by coexpression of PINK1, parkin or DJ-1 but not the PD-associated mutations PINK1 G309D and parkin 1-79 or by DJ-1 C106A.

El Mouridi, Sonia et al. (2021) MicroPubl Biol

AlHarbi, Sarah, El Mouridi, Sonia, Frkjr-Jensen, Christian

[MicroPubl Biol, 2021]

For El Mouridi, S; AlHarbi, S; Frkjr-Jensen, C (2021). A histamine-gated channel is an efficient negative selection marker for C. elegans transgenesis. microPublication Biology. 10.17912/micropub.biology.000349.