Katzen, Abraham et al. (2015) International Worm Meeting "Economic decision-making and neural correlates of value in C. elegans."

Harbaugh, William, Katzen, Abraham, Lockery, Shawn

[International Worm Meeting, 2015]

Investigation of the neuronal basis of economic decisions would be accelerated by establishing decision making paradigms in simple, genetically tractable organisms, such as the nematode Caenorhabditis elegans. For an organism to be a valid model of economic decision making its choice behavior must be sensitive to: (i) the difference between high and low quality goods, and (ii) the relative cost of those options.Previous work has shown that the nematode worm C. elegans quickly learns to feed on those foods (species of bacteria) that promote higher rates of growth and reproduction. Worms spend more time foraging in patches of Good bacteria (high worm growth rate) versus Mediocre bacteria (moderate growth rate) when equally abundant. Until now, however, it has not been possible to simultaneously present two food choices of different quality and cost. To that end, we have developed an electro-microfluidic device in which a semi-restrained worm forages between contiguous yet discrete fluid streams containing good and mediocre quality food. This arrangement constitutes a two-alternative forced-choice task, analogous to those used in behavioral economics. Electrodes inserted into the device monitor muscular impulses associated with individual swallowing events. Relative consumption of Good and Mediocre food is measured by counting the number of swallowing events in the respective fluid streams. The fraction of total swallowing events in Good vs Mediocre food serves as an index of food preference. Importantly, we can alter the effective prices of the two foods by adjusting the concentration of the bacteria, with price being inversely related to concentration.Here we present behavioral data delineating preference for Good vs Mediocre food across a range of relative prices. We find that worms exposed to the two species of bacteria at equal prices prefer Good bacteria, indicating that feeding preferences are normal in the device. Worms respond to price adjustments as predicted by economic theory in that increasing the relative price of a food leads to a decline in its consumption. In addition, we present calcium-imaging data from sensory neurons showing that they respond to transitions between Good and Mediocre foods, and the amplitude of calcium signal scales with relative food preference. These results show that C. elegans forages in an economic manner, and that relative value is represented at the level of the sensory neurons.

Katzen, Abraham et al. (2021) International Worm Meeting "C. elegans chooses food exactly as if maximizing economic utility"

Della Iacono, Christina, Glimcher, Paul, Jackson, Nicholas, Harbaugh, William, Chung, Hui-Kuan, Katzen, Abraham, Lockery, Shawn

[International Worm Meeting, 2021]

The well-functioning brain makes decisions that maintain and improve the animal's welfare. These decisions are based on subjective values assigned by the chooser to available goods and actions. However, the neural mechanisms of value assignments, and choices based on them, remain obscure. To investigate this problem, we used a classic measure of utility maximization, the Generalized Axiom of Revealed Preference, to quantify internal consistency of food preferences in Caenorhabditis elegans, a nematode worm with a nervous system of only 302 neurons. Using a novel combination of microfluidics and electrophysiology, we found that C. elegans food choices fulfill the necessary and sufficient conditions for utility maximization. Moreover, as in many other animals, preferences are learned, a process we found to require intact dopamine signaling. Preferences are expressed as a modulation of the worm's normal foraging movements rather than feeding rate. Food-specific responses of identified chemosensory neurons known to direct foraging are strengthened by training, suggesting they may be part of the value-assignment system. The demonstration of utility maximization in an organism having a nervous system of only 302 neurons sets a new lower bound on the neuronal requirements for its execution, and offers the prospect of an essentially complete explanation of value-based decision making at single neuron resolution.

Shelli N Williams et al. (2001) International C. elegans Meeting "Phenotypic Crosstalk Between the LIS-1 and Cdk5 Pathways in C. elegans"

Guy A Caldwell, Shelli N Williams, Kim A Caldwell

[International C. elegans Meeting, 2001]

Cdk5 and its activators p35 and p39 are well-studied genes found to be expressed predominantly in neuronal cell types and to play roles in both neuronal migration events and myogenesis. However, unlike other activator/cyclin-dependent kinase complexes, Cdk5, complexed with either p35 or p39, has not been implicated in cell cycle regulation. Previous work has indicated that the C. elegans homologues of Cdk5 and p35 are both neuronally expressed by translational GFP reporter constructs and may play a role in neuronal development (Harbaugh and Garriga, 2000 West Coast Worm Meeting). Interestingly, our lab has found embryonic phenotypes associated with these genes through both p35 and cdk-5 RNAi experiments and an analysis of mig-18(k140) embryos (a putative allele of cdk-5 ). The embryonic phenotypes associated with deficiencies in cdk-5 include pronuclear migration and rotation defects in one-celled embryos. In p35 (RNAi) embryos, centrosome mispositioning also occurs. Furthermore, offspring of worms fed either p35 or cdk-5 dsRNA, individually or in combination, exhibit uncoordinated phenotypes. Recently, several groups (Neuron 28:665-711) have shown a connection between the Cdk5 and LIS-1 pathways in higher organisms, previously believed to be separate mechanisms in brain development. Our work supports these findings, as we have examined the consequence of p35 and cdk-5 RNAi on lis-1 ::GFP expression patterns, wherein we find altered neuronal expression. Moreover, we observe enhanced uncoordinated phenotypes when combining lis-1 dsRNA with either p35 or cdk-5 dsRNA. In addition, we have found phenotypic changes in embryos from parental worms fed combinations of lis-1 , p35, and cdk-5 dsRNA, including centrosome duplication and positioning errors. Taken together, these results seem to indicate a connection between the neuronal and embryonic development pathways mediated by cdk-5 and lis-1 in C. elegans .

Frederick A. Partridge et al. (2006) European Worm Meeting "The Glycosyltransferase BUS-8 is Essential for Epidermal Morphogenesis"

Jonathan Hodgkin, Frederick A. Partridge, Adam W. Tearle, Maria J. Gravato-Nobre, William R. Schafer

[European Worm Meeting, 2006]

Frederick A. Partridge1, Adam W. Tearle2, Maria J. Gravato-Nobre1, William R. Schafer2 and Jonathan Hodgkin1. In C. elegans the epidermis is a simple epithelium. It is derived from a sheet of cells on the dorsal side of the embryo that spread to enclose the ventral side prior to elongation. The epidermis is then covered by the cuticle, an extracellular structure. We independently isolated alleles of bus-8 in screens for mutants resistant to infection by Microbacterium nematophilum and for nicotine hypersensitivity. Further alleles were obtained from a non-complementation screen, and a deletion (putative null) allele was provided by Shohei Mitani. bus-8(null) animals arrest during embryogenesis. We have shown that this is due to a defect in ventral enclosure, leading to extrusion of the body contents through the anterior of the ventral side during early elongation. This is reminiscent of mutations in the cadherin hmr-1. Weaker alleles of bus-8 show a variety of larval defects, including hypersensitivity to a variety of drugs. We have examined the structure of the cuticle and epidermis by electron microscopy. The epidermis is strikingly disordered. We also see abnormalities in the surface coat and cuticle. We propose that, due to their abnormalities in epidermal morphogenesis, bus-8 mutants are more permeable to small molecules. We have cloned bus-8. It encodes a putative glycosyltransferase. This suggests that glycosylation may have a role in mediating cadherin-based adhesion. We will discuss our progress at relating the molecular identity of bus-8 to its roles during development.

Stefan Eimer et al. (2006) European Worm Meeting "The Integral Membrane Protein UNC-50 is required for Nicotinic Receptor Trafficking in C. elegans"

Janet Richmond, Alexander Gottschalk, Michael Hengartner, Stefan Eimer, Jean-Louis BESSEREAU, William R Schafer

[European Worm Meeting, 2006]

Stefan Eimer1, Alexander Gottschalk2, Janet Richmond3, Michael Hengartner4, William R Schafer2, and Jean-Louis Bessereau1. Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels that undergo multiple assembly, modification and transport steps prior to insertion into the plasma membrane. However, little is known about the molecules that are specifically participating in these processes. In C. elegans a nAChR sensitive to the nematode-specific cholinergic agonist levamisole has been well characterised. Mutants in all of its four subunits confer resistance to muscle hyper-contraction and death upon exposure to levamisole.. Similarly, unc-50 mutant animals exhibit the same resistance to paralysis and death upon exposure to levamisole. By antibody staining and electro-physiological recording of body-wall muscles we show that levamisole receptors are not detectable at cell surface in unc-50 mutants. However, a second type of muscle nAChR, which is insensitive to levamisole, and the GABA receptor are normally transported to the synapse. unc50 encodes an integral membrane protein conserved from yeast to man. In C. elegans, unc-50 is ubiquitously expressed and localized to the Golgi system. We showed that UNC-50 is required in body wall muscles for the transport of the assembled levamisole receptor to neuromuscular junction. In the absence of UNC-50 the receptor is sorted within Golgi to the lysosomal system and rapidly degraded. Therefore, UNC-50 might be part of/constitute a Golgi resident check point during levamisole receptor transport. UNC-50 interacts with the GBF1 class of large Arf GEFs which are involved in retrograde transport within the Golgi system. Models how retrograde transport and sorting would required for levamisole receptor trafficking will be discussed.

Marina Ezcurra et al. (2006) European Worm Meeting "Analysis of the Role of npr-1 in Responses to Noxious Stimuli in ASH"

Peter Swoboda, William R. Schafer, Sunkyung Lee, Marina Ezcurra

[European Worm Meeting, 2006]

Marina Ezcurra, Sunkyung Lee, Peter Swoboda and William R. Schafer. Discrimination of favorable and noxious substances is fundamental for survival. The C.elegans polymodal amphid neuron ASH is the primary neuron for detection of aversive stimuli, and mediates avoidance of water-soluble repellents, high osmolarity and mechanical stimuli such as touch on the nose. npr-1 encodes a seven transmembrane receptor related to mammalian neuropeptide Y receptors. As shown by de Bono et al, natural variation at a single amino acid residue of NPR-1 determines whether the nematodes exhibit solitary or social feeding. Solitary strains such as N2 bear the NPR-1 215 V receptor, while social strains bear NPR-1 215F. Previous studies have shown that ASH neurons express the NPR-1 receptor, and since social feeding is mediated by the nociceptive neuron ASH, we investigated whether how the npr-1 genotype might affect ASH sensory responses. Preliminary behavioral experiments performed in the lab show that npr-1 mutants have higher sensitivity to the repellents glycerol and copper, indicating that the lower NPR-1 activity in 215F might result in higher sensitivity to noxious stimuli. We are carrying out additional behavioral experiments to explore the role of npr-1 in response to noxious stimuli, and using calcium imaging to investigate the role of npr-1 in aversive detection in ASH.. In addition to ASH, ASK and ADL also play roles in detection of chemical repellents. ASK is particularly interesting as it mediates both attractive and repulsive behaviors in C. elegans, but it is not yet know how this polymodality is mediated. Several genes expressed in ASK, such as the TRPV channel osm-9, the soluble cyclic nucleotide gated channel subunit tax-4, and the GPCR alpha subunits gpa-3 and odr-3, are known to be involved in sensory transduction. To test the role of these and other genes in ASK, we have generated a transgenic cameleon line expressed under an ASK specific promoter. This line will be used for calcium imaging to monitor the responses of ASK in mutants of the candidate genes.

Sadler, Penny L. et al. (2011) International Worm Meeting "Using C. elegans to teach transmission genetics in a large introductory biology lab."

Sadler, Penny L., Shakes, Diane C.

[International Worm Meeting, 2011]

Transmission genetics is a core topic in most introductory biology courses and yet many students rarely think about genetics beyond Mendel's classical experiments with peas. In our introductory biology laboratory course at the College of William and Mary, we expand students' notions of transmission genetics by using C. elegans as the model system to determine whether an "unknown" Unc mutation is linked or unlinked to a known Dpy marker. In a course that serves not only biology majors but also neuroscience majors, pre-meds, and non-majors, the students see direct relevance in studying mutations with direct links to human neurological conditions. Our genetics module is a four-week session that culminates in a writing workshop designed to aid students in writing their first formal lab report. The first week serves as an introduction to best practices in using a dissecting scope, sexing the worms, distinguishing single mutant morphological phenotypes, and setting up a Po cross with 1mm long males and hermaphrodites. During the second week, the students score their P0 cross, set up their F1 crosses, and practice distinguishing wild type, single mutants and double mutant hermaphrodites. During the third week, the students score their F2 progeny, analyze their data, and test their data set against a null hypothesis that the two genes are unlinked using Chi-square. The format of the lab report is introduced and discussed as a class. During the fourth week, student teams meet with their lab instructor to go over a rough draft of their lab report. This one-on-two time dedicated to improving the content of the report allows for correction of major misconceptions and errors in formatting the report. The fourth lab week is also dedicated to a self-guided online Wormbase bioinformatics exercise which is designed to help students formulate their ideas for the future directions sections of their lab report. The poster will also present student learning objectives and assessment, and discuss the logistics of preparing the materials that enable over 400 freshmen carry out a series of genetic crosses during a four week lab module under the guidance of masters level graduate teaching assistants and a single, full-time lab coordinator.

William C. Chen et al. (2006) European Worm Meeting "Using C. elegans Chromosome Substitution Strains to Map Innate Immunity Loci"

William C. Chen, Sandra S. Slutz, Man-Wah Tan

[European Worm Meeting, 2006]

William C. Chen1, Sandra S. Slutz1, and Man-Wah Tan. The genome of the Hawaiian natural isolate (CB4856) of Caenorhabditis elegans contains thousands of SNPs that differ from Bristol N2. Wicks et al. proposed a method for mapping mutations generated in the N2 background by genotyping snip-SNPs in crosses between mutants and the Hawaiian strain [1]. However, some polymorphisms lead to functional differences between the two strains that affect a variety of phenotypes such as social feeding, germline RNAi, and immunity [2-4]. We found that the Hawaiian strain has increased susceptibility to Pseudomonas aeruginosa. In order to identify the loci responsible for the Hawaiian sensitivity, recombinant inbred lines between Hawaiian and N2 were created. Analysis of these lines shows that changes at multiple loci cause the observed Hawaiian pathogen sensitivity phenotype. Separately, we have EMS mutagenized N2 worms to obtain mutants with enhanced susceptibility to pathogen (Esp); however, we have been unable to map these mutants using Hawaiian due to Hawaiians sensitivity to pathogen. In order to map our Esp mutants and to identify the Hawaiian immunity loci, we have created N2/Hawaiian chromosome substitution strains (CSSs). Each of these six strains (five autosomes and the X chromosome) contains a single homozygous Hawaiian chromosome substituted into an N2 background. CSSs have been used in mice to map quantitative trait loci, and we reasoned that a similar strategy could identify loci that contribute to the Hawaiian phenotype [5]. Importantly, those CSSs that are like N2 for sensitivity to pathogen can be used to map Esp mutations that occur on the same chromosome.. We will report on using the CSSs to identify Hawaiian specific innate immunity loci and the mapping of Esp mutants from our mutagenesis screen. We believe that these CSSs will be a valuable resource for other researchers who have been unable to use the Hawaiian strain for mapping their own mutants due to the differences in phenotypes between Hawaiian and N2. 1. Wicks, S.R., et al., Nature Genetics, 2001. 28(2): p. 160-164.. 2. de Bono, M. and C.I. Bargmann, Cell, 1998. 94(5): p. 679-689; 3. Schulenburg, H. and S. Muller. Parasitology, 2004. 128(4): p. 433-443; 4. Tijsterman, M., et al., Current Biology, 2002. 12(17): p. 1535-1540; 5. Singer, J.B., et al., Science, 2004. 304(5669): p. 445-448.