Grenache DG et al. (1993) Worm Breeder's Gazette "Differential Effects of Dauer-Defective Mutations in L1-Specific Surface Antigen Switching"

Politz SM, Grenache DG

[Worm Breeder's Gazette, 1993]

DIFFERENTIAL EFFECTS OF DAUER-DEFECTIVE MUTATIONS ON L1- SPECIFIC SURFACE ANTIGEN SWITCHING. David G. Grenache and Samuel M. Politz, Department of Biology and Biotechnology, Worcester Polytechnic Institute, Worcester, MA.

Hendricks, Michael et al. (2013) International Worm Meeting "Sensory responses to graded stimuli: a role in bidirectional chemotaxis?"

Samuel, Aravi, Linjiao, Luo, Hendricks, Michael, Zhang, Yun

[International Worm Meeting, 2013]

C. elegans can migrate up or down salt gradients toward a remembered cultivation concentration. Both positive and negative chemotaxis are driven by biased random walks of opposite sign, and the chloride-sensing neuron ASER is required for chemotaxis in both directions. We are interested in how the same neural circuit can mediate opposite behaviors. Responses of ASER, measured with genetically-encoded calcium indicators, have been previously examined in response to large, abrupt step changes in salt concentration. However, during chemotaxis assays, crawling animals experience smooth changes in salt concentration. To better match behavioral conditions, we exposed semi-restrained worms to quasi-linear graded changes in salt concentration that match what is experienced by animals migrating on plates (~50 mM/s). ASER shows sustained activity in response to decreasing salt gradients, however the temporal dynamics of these responses differ depending on whether the animals are being tested above or below their cultivation concentration. ASER exhibits activity during increases in salt concentration only above its cultivation concentration. Thus, ASER responses can represent both the direction of the temporal salt gradient and whether it is "toward" or "away" from a remembered set point. We hypothesize that downstream interneurons differentially integrate or respond to the various activity patterns in ASER.

Adam Brown et al. (2003) International Worm Meeting "Genetic analysis of AFD thermosensory neuron function in C. elegans."

Adam Brown, Piali Sengupta

[International Worm Meeting, 2003]

Thermosensation plays an important role in the development, metabolism, and behavior of animals. C. elegans can be used to genetically dissect thermosensation, as they demonstrate distinct behaviors in response to temperature gradients. Genetic and laser ablation experiments have identified a circuit of neurons responsible for this behavior, including the primary temperature sensing neuron type, AFD. However, little is known about how AFD mediates its functions, as well as how worms form the "memory" of their cultivation temperature that modulates this behavior. Previously, a screen for mutations that alter the expression of a fusion gene gcy-8::gfp expressed specifically in the AFD neuron pair was performed in our lab to investigate AFD development and function. This screen led to the identification of the Otx/Otd-like homeobox transcription factor gene ttx-1, which is necessary and sufficient to specify AFD fate (Satterlee et al, 2001), and the cmk-1 CaMKI ortholog (see abstract by Satterlee and Sengupta). We are currently continuing this screen to identify further components of the AFD developmental and sensory pathways. We have screened the progeny of over 25,000 haploid genomes and identified a number of mutants. It is expected that a subset of these mutants may define additional genes required for both the function and development of the AFD neurons. Additionally, we also plan to carry out thermosensory behavioral screens to identify mutants with defects in distinct aspects of thermosensation. Finally, in collaboration with Will Ryu and Aravi Samuel (Rowland Institute, Harvard University), we have initiated behavioral analyses of both new and existing signaling mutants in an attempt to further dissect the neuronal pathways and molecules required for thermosensory behaviors.

Politz SM et al. (1992) Parasitol Today "Caenorhabditis elegans as a model for parasitic nematodes: a focus on the cuticle."

Philipp M, Politz SM

[Parasitol Today, 1992]

The phylum Nematoda consists of over half a million species of worms that inhabit astoundingly diverse environments. Nematodes can live as obligatory parasites of plants and animals, or alternate a parasitic with a free-living life style. The fact that the vast majority of species are strictly free living often surprises parasitology students, for obviously the highest research priorities in this field have involved parasites of medical, veterinary and agricultural importance. Here Samuel Politz and Mario Philipp contend that some basic questions concerning the biology of the parasite cuticle can be investigated more easily and in greater depth in the free-living nematode Caenorhabditis elegans than in the parasites themselves.

Nikhil Bhatla et al. (2008) C.elegans Neuronal Development Meeting "Reduction of Movement by flp-11, which Encodes FMRFamide-related Peptides"

Bob Horvitz, Nikhil Bhatla, Niels Ringstad

[C.elegans Neuronal Development Meeting, 2008]

FMRFamide-related peptides (FaRPs) make up a large and diverse family of C. elegans neuropeptides. To learn how these peptides control C. elegans behavior, we overexpressed genes predicted to encode FaRPs (the flp genes) and characterized the resulting behavioral defects. Overexpression of flp-11 from an integrated transgene greatly reduces locomotion compared to the wild type. We quantified this reduction in movement using a wormtracker (developed by Damon Clark, Aravi Samuel, and Dan Omura) and found that the average speeds of flp-11 transgenic strains are less than 50% of the wild-type speed. We also quantified locomotion by body bend counts: flp-11 overexpressors execute 70% fewer body bends per unit time than the wild type. The overexpressors lay motionless more often and, when they are moving, move more slowly than normal. To identify genes involved in the flp-11 overexpression phenotype, we screened EMS-mutagenized flp-11 overexpressors for suppressors of the locomotion defect. An F2 non-clonal screen of 20,000 haploid genomes yielded 1 suppressor, and an F1 clonal screen of 2,500 haploid genomes isolated 2 suppressors. These suppressors all exhibit average speeds similar to the wild-type speed. We are currently mapping these 3 suppressors. We are also planning to measure the speed of a flp-11 deletion mutant. To identify neural circuits that use flp-11 to control behavior, we have constructed a flp-11::GFP translational fusion reporter gene. Transgenic worms show GFP expression in a single cell near the posterior bulb of the pharynx. We plan to characterize the functions of flp-11-expressing cells by laser-ablation experiments. We are also searching for flp-11 receptors through our suppressor screens and by testing candidate genes. Identification of flp-11 receptors will help us identify the sites of action of flp-11 neuropeptides.

Laskova, Valeriya et al. (2013) International Worm Meeting "Mapping the entire connectome of C. elegans L1 larvae."

Zhen, Mei, Kasthuri, Bobby, Shalek, Richard, Lichtman, Jeff, Samuel, Aravi, Pfister, Hanspeter, Laskova, Valeriya, Kaynig-Fittkau, Verena, Wen, Quan, Berger, Daniel, Guan, Asuka

[International Worm Meeting, 2013]

To investigate the poorly understood mechanisms of development and function of the nervous system, connections between neurons must be deciphered first. The adult nervous system of C. elegans was mapped to near completion by Dr. John White and his colleagues in 1970s. However, neuronal wiring in C. elegans larvae differs from that of an adult, since it undergoes multiple rounds of neuronal birth, apoptosis and rewiring during development. We utilize an Automatic Tape-Collecting Ultramicrotome (ATUM) to section an entire L1 stage animal into thousands cross-sections, followed by the automated imaging with a scanning electron microscope (SEM) to map an entire neuronal wiring diagram with synaptic resolution. The acquired wiring diagram will guide and be validated by calcium imaging to map the functional connection of the juvenile motor circuit.

Monica Driscoll (2008) C.elegans Neuronal Development Meeting "Neuronal Degeneration, Aging and Regeneration in C. elegans"

Monica Driscoll

[C.elegans Neuronal Development Meeting, 2008]

The amazing cellular characterization of the C. elegansnervous system (thanks, John White and colleagues!), coupled with the power of molecular and genetic manipulations that can be applied in this transparent nematode, render the worm a highly appealing model for the investigation of conserved mechanisms of neuronal degeneration, aging and regeneration. Like in mammals, C. elegans necrotic death can be initiated by hyper-activated ion channels of two types: DEG/ENaCs, and glutamate-gated channels. Death-inducing mutations hyperactivate the Ca/Na-permeable MEC-4(D) DEG/ENaC channel, which induces catastrophic ER calcium release and activates proteases to induce necrotic death. MEC-4-related Ca-permeable DEG/ENaC ASIC1a is hyperactivated in ischemia to induce neuronal loss in mouse brain. Also in mammalian stroke, neuronal over-stimulation by glutamate (Glu) hyperactivates post-synaptic Glu receptor ion channels (GluRs) and triggers excitotoxic neurodegeneration. Malfunction of surface glutamate transporters (sGluTs), which normally remove Glu from the synapse, elevates local synaptic glutamate concentration to induce excitotoxicty. We have found that deletion of sGluT glt-3 acts synergistically with activated Gas* signaling to promote extensive necrosis, acting through GluRs of the AMPA subtype and Type 9 calcineurin-modulatedadenylyl cyclase acy-1. Our hope is that genetic and pharmacological analyses of C. elegans necrosis will provide insight applicable into preventing neuronal loss in the clinic. Our interest in neurodegeneration provoked a natural curiosity about the aging of the C. elegans nervous system and potential contributions of neuronal degeneration to aging. Our studies revealed that neuronal death per se does not drive the aging of the animal. Rather, more subtle changes in the nervous system apply. Stochastic factors seem to exert a major impact on the aging of the animal and the nervous system. After years of research focus on death and deterioration, we sought to add in a more positive topic of study. We are collaborating with Aravi Samuel''s lab to address the role of cell death machinery in the process of neuronal regeneration consequent to laseraxotomy (see abstracts by Pinan-Lucarre, Gabel, et. al.; Gabel et al.). These studies have revealed a role for CED-3 caspase as well as ER calcium-storing chaperone calreticulin in a cell-autonomous mechanism of neuronal regeneration, suggesting that the bad boys of apoptosis and necrosis can make good.

Gadagkar R (1998) Trends in Ecology & Evolution "How to gain the benefits of sexual reproduction without paying the cost: a worm shows the way."

Gadagkar R

[Trends in Ecology & Evolution, 1998]

Sexual reproduction is perhaps the greatest of all evolutionary puzzles. It's a puzzle because sexually reproducing species pay the cost of spending half their resources (over and above what is needed for vegetative growth) in producing males, whereas parthogenetic species utilize all their resources meant for reproduction in producing only females (or hermaphrodites) like themselves. This twofold cost of sexual reproduction is sometimes referred to as the twofold cost of producing males. Three advantages of sexual reproduction that might offset this cost have been proposed. Genetic recombination and cross fertilization permit sexually reproducing species to (1) bring together, in the same individual, mutations arising in different individuals; (2) generate genetic variability and thus adapt to changing environments; and (3) shuffle their genes in every generation and thus keep parasites at bay. While evolutionary biologists are busy testing their favourite ideas for offsetting the twofold cost of producing males, recent work by Craig LaMunyon and Samuel Ward shows that a nematode, Caenorhabditis briggsae, appears to have found a way of gaining the benefits of sexual reproduction without paying the cost of producing males.

Yemini, E.I. et al. (2017) International Worm Meeting "Whole-Brain Imaging with Single-Neuron Identity in C. elegans."

Venkatachalam, V., Yemini, E.I., Hobert, O., Samuel, A.D.

[International Worm Meeting, 2017]

Stereotypy of the C. elegans nervous system affords single-neuron registration across animals, and consequently, robust statistics for neurobehavioral coding and transcriptomics. Fast methods of whole-brain imaging in worm exist, but unfortunately determining the identity of neurons within these volumes remains a bottleneck - requiring a long, difficult, ad hoc process. We have developed a landmarked strain for whole-brain neural identification, NeuroPAL (a Neuronal Polychromatic Atlas of Landmarks). Each neuron is assigned an invariant fluorophore barcode such that color and position specify unambiguous neural identity via the unique 3-tuple (color, position, ganglion). The GFP channel is preserved for reporters of neural activity (GCaMP) and transcriptomics (GFP). Our landmark strain employs 5 fluorophores. To visualize this strain we have used a new microscope, developed by the Samuel lab, with the capability of imaging 9 unique fluorescence channels generated by 4 excitation lines and 4 emission bands. This microscope acquires whole-brain volumes, of 4 fluorophores, simultaneously, at 10Hz. Together, these two innovations permit fast whole-brain imaging, with single-neuron identity and neuronal registration, across an animal populace.

Mulcahy, Ben et al. (2017) International Worm Meeting "The Dynamics of Synaptic Remodeling: insights from the C. elegans Motor Circuit."

Holmyard, Douglas, Christensen, Ryan, Lichtman, Jeff, Koh, WanXian, Witvliet, Daniel, Schroff, Hari, Mitchell, James, Qu, Yixin, Chisholm, Andrew, Samuel, Aravi, Bermant, Peter, Schalek, Richard, Zhen, Mei, Mulcahy, Ben, Chang, Maggie, Fetter, Rick

[International Worm Meeting, 2017]

During development, neural circuits undergo constant changes: they incorporate new neurons, and maintain, prune or remodel existing synapses. The small and rapidly developing nervous system of C. elegans allows us to address the developmental dynamics of synapses and neurons in the context of an intact neural ensemble. The vast majority of C. elegans postembryonic neurons are motor neurons. Previous studies suggest that at least one group of motor neurons, DD, reverse their neurite polarity entirely: they innervate ventral body wall muscles in the first larval stage, whereas they innervate dorsal muscles in adults. Their role of innervating ventral muscle is taken over by a group of post-embryonically born motor neurons, VD. Precisely how and when such processes occur, without disrupting motility as the motor circuit transitions into the adult form, is poorly described. We used serial section electron microscopy to reconstruct DD and VD motor neurons across development to define the beginning and ending of remodeling. We identified a series of elegantly coordinated synaptogenesis and remodeling events where synaptogenesis events follow different sequential orders for embryonic (DD) and post-embryonic (VD) neurons. Developing VD neurons have some interaction with DD neurons that may help to guide neurite extension and synaptogenesis. These events implicate an elegant mechanism that allows a gradual and seamless transition of the motor circuit to take place without disrupting its functional output.