Bruce A Bamber et al. (2005) International Worm Meeting "Homeostatic regulation of the UNC-49 GABAA receptor"

Janet E Richmond, Aaron M Rowland, Alice Benham, Bruce A Bamber

[International Worm Meeting, 2005]

Inhibitory synaptic strength depends on the density of postsynaptic GABAA receptors. Plasticity of postsynaptic GABAA receptor density contributes to homeostatic regulation in the nervous system, and is associated with disease states such as epilepsy and anxiety. To understand the mechanisms that control GABAA receptor density at synapses, we are studying the inhibitory neuromuscular junction in C. elegans. When exposed to the GABA agonist muscimol, worms initially become paralyzed, but then adapt. Adapted worms have a shrinker Unc phenotype characteristic of worms that lack GABA neurotransmission. We hypothesized that adaptation is the result of downregulation of GABAA receptors at the neuromuscular junction, which are encoded by the unc-49 gene. We tested this hypothesis by comparing GABA currents in naïve and muscimol-adapted worms. GABA currents were six-fold reduced in amplitude in adapted animals. Using quantitative immunofluorescence, we demonstrated that UNC-49 abundance at the synapse was reduced nine-fold. A transcriptional mechanism does not appear to be involved: quantitative RT-PCR analysis demonstrated that unc-49 mRNA levels were reduced, but only transiently. unc-49 mRNA returned to its pre-exposure level before the majority of the protein was lost. Using the immunofluorescence assay, we are characterizing protein trafficking and cell signaling mutants to understand the mechanism of this homeostatic regulation of the UNC-49 GABAA receptor.

Bruce A Bamber et al. (2005) International Worm Meeting "Identification of residues that confer neurosteroid sensitivity on the UNC-49 GABAA receptor"

Bryan Wardell, Bruce A Bamber, Purba S Marik, Erik M Jorgensen

[International Worm Meeting, 2005]

We are using the C. elegans GABAA receptor, encoded by unc-49, to study the structural basis of neurosteroid action. Neurosteroids are endogenous steroid molecules that control many aspects of mammalian nervous system function, principally by modulating GABAA receptors. Attempts to identify residues involved in neurosteroid modulation using standard domain swap approaches have been unsuccessful to date because there is little variation in neurosteroid sensitivity among mammalian GABAA receptors. UNC-49 provides a solution to this problem. The unc-49 gene encodes two subunits, UNC-49B and UNC-49C, by alternative splicing. Normally these subunits coassemble to form a heteromultimer, which is highly sensitive to the inhibitory neurosteroid pregnenolone sulfate. However UNC-49B also forms a homomultimer which is insensitive to pregnenolone sulfate. By swapping segments of UNC-49C in to UNC-49B, followed by site-directed mutagenesis, we have identified seven important residues. When mutated together, these residues produce a 58-fold increase in pregnenolone sulfate sensitivity. These mutations have little effect on other allosteric regulators, suggesting they may be specific for neurosteroids. The residues cluster in regions important for channel gating, suggesting that pregnenolone sulfate binding changes how key gating residues are positioned, or move during GABA activation, resulting in decreased channel function.

Maske B et al. (1994) Worm Breeder's Gazette "Localization of SKN-1 Protein to Posterior Blastomere in the Early C. elegans Embryo"

Maske B, Bowerman BA, Lommel S

[Worm Breeder's Gazette, 1994]

LOCALIZATION OF SKN-1 PROTEIN TO POSTERIOR BLASTOMERES IN THE EARLY C. ELEGANS EMBRYO. Bill Maske, Silvi Lommel, and Bruce Bowerman. Institute of Molecular Biology, University of Oregon, 97403.

Shoman LM et al. (1994) Worm Breeder's Gazette "Worm Community System Users Envision Future Application."

Grossman E, Shoman LM, Jamison DC, Schatz BR

[Worm Breeder's Gazette, 1994]

Worm Community System Users Envision Future Application. Laura Shoman, Curt Jamison, Ed Grossman, Bruce Schatz, Community Systems Laboratory, National Center for Supercomputing Applications, University of Illinois, Urbana- Champaign, 405 North Mathews, Urbana, IL 61801 (wcs@csl.ncsa.uiuc.edu)

Chamberlain SH et al. (1994) Worm Breeder's Gazette "A Molecular Approach to Identify skn-1-Responsive Genes in the Early C. elegans Embryo"

Chamberlain SH, Bowerman BA

[Worm Breeder's Gazette, 1994]

A molecular approach to identify skn-1-responsive genes in the early C. elegans embryo. Stephen H. Chamberlain and Bruce Bowerman, Institute of Molecular Biology, University of Oregon, Eugene, OR 97403

Debnath, Arunima et al. (2021) International Worm Meeting "Neuromodulation and the relationship between Ca2+ transients and neuronal states"

Bamber, Bruce, Debnath, Arunima

[International Worm Meeting, 2021]

Neuromodulators (monoamines and neuropeptides) shape nervous system function by regulating neuronal depolarization and synaptic strengths. We are studying neuromodulation in the context of nociception, to better understand pain perception and pain treatment strategies. The ASH neuron is a major nociceptor in C. elegans. ASH senses 1-octanol and drives an aversive response, modulated by the monoamines serotonin (5-HT, potentiating) and octopamine (OA, inhibitory). To better understand neuromodulation, we are focusing on 1-octanol stimulated Ca2+ dynamics in ASH, and the quantitative relationship between Ca2+ signals and depolarization amplitudes. We showed that 5-HT potentiates ASH depolarization, but surprisingly, inhibits ASH Ca2+ transient amplitudes. These effects, like the 5-HT stimulation of behavior, depend on the SER-5 receptor in ASH. This paradoxical finding is explained by existence of a Ca2+-dependent inhibitory feedback loop: Ca2+ inhibits ASH depolarization through SLO-1 IKCa channels, and 5-HT inhibits EGL-19 L-type Ca2+ channels in ASH (via SER-5), thus disinhibiting the neuron. We are currently investigating modulation of 1-octanol responses by OA. OA inhibits 1-octanol behavioral responses, and antagonizes 5-HT potentiation, dependent on the OCTR-1 receptor in ASH. OA also inhibits ASH Ca2+ transients, representing another paradox: how can OA and 5-HT have opposite effects on ASH-dependent aversive behaviors, but the same effect on ASH Ca2+ transients? Our results show that 5-HT and OA utilize distinct signaling pathways in ASH (Galphaq for 5-HT and Galphao for OA), and that OA does not inhibit EGL-19. We are currently testing the hypothesis that OA hyperpolarizes ASH through Galphao-dependent activation of IRK K+ channels. These results further emphasize that neuronal Ca2+ transients, as key reporters of neuronal depolarization, are also critical signaling intermediates in and of themselves, with multiple upstream inputs and downstream consequences.

Bowerman BA et al. (1994) Worm Breeder's Gazette "The Maternal Gene skn-4 and the Specification of Ventral Blastomere Fates in the Early C. elegans Embryo"

Bowerman BA, Shelton CA, Thorpe CJ, Martin PR

[Worm Breeder's Gazette, 1994]

THE MATERNAL GENE SKN-4 AND THE SPECIFICATION OF VENTRAL BLASTOMERE FATES IN THE EARLY C. ELEGANS EMBRYO Bruce Bowerman, Paula R. Martin, Christopher J. Thorpe, and Christopher A. Shelton. The Institute of Molecular Biology, University of Oregon, Eugene, OR 97403.

Zahratka, Jeffrey et al. (2013) International Worm Meeting "Multiple independent calcium pools in a nociceptive neuron in C. elegans."

Bamber, Bruce, Komuniecki, Richard, Zahratka, Jeffrey, Williams, Paul

[International Worm Meeting, 2013]

To navigate constantly changing environments, animals integrate sensory inputs and internal state information to formulate proper locomotory commands. Monoamines and neuropeptides encode internal state information, modulating sensorimotor circuits at several levels, including the sensory neurons themselves. We study aversive behaviors in C. elegans to better understand how neuromodulators affect circuit function, in terms of the physiological states of single identifiable neurons. C. elegans reacts to the noxious odorant 1-octanol by reversing locomotory direction, to move away from the odor source. Worms off food respond to diluted 1-octanol in 10s, but in the presence of food, response time shortens to 5s. Endogenous 5-HT and neuropeptides are key signaling intermediates in this food-dependent modulation, relying in part on a 5-HT receptor (SER-5) in the ASHs (the pair of nociceptive neurons that sense 1-octanol). Using the GCaMP3 Ca++ indicator, we show that a saturating concentration of 1-octanol dissolved in buffer (~2 mM) elicits robust excitation of ASHs when applied to the nose. At least 3 distinct Ca++ pools exist in ASHs: distal dendrite, proximal dendrite/soma, and axon. Proximal dendrite/soma Ca++ responses are sensitive to Nemadipine-A, a blocker of L-type Ca++ channels. Distal dendrite responses, and more importantly, axonal responses are resistant to Nemadipine-A. This finding suggests that somal Ca++ influx is unnecessary for signal propagation from one end of the cell to the other, consistent with isopotentiality within C. elegans sensory neurons. What then is the role of somal Ca++ influx? Rather than amplifying or relaying chemosensory signals to axons, we hypothesize it is intermediate in sensory modulation, and in support, monoamine signals regulating aversive behavior also regulate ASH somal Ca++ signals. We are currently testing whether the different Ca++ pools within ASHs are the result of regionalized expression of Ca++ channels, characterizing the monoamine and neuropeptide signaling cascades affecting ASH somal Ca++, and elucidating the roles for ASH somal Ca++ by direct measurement of ASH synaptic release onto postsynaptic targets and behavioral assays.

Summers, Philip et al. (2015) International Worm Meeting "Modulation of glutamatergic signaling in C. elegans."

Komuniecki, Richard, Summers, Philip, Ortega, Amanda, Bamber, Bruce

[International Worm Meeting, 2015]

The glutamatergic ASH sensory neurons are essential for the initiation of aversive responses to dilute 1-octanol. To identify and localize the glutamate receptors involved, we screened animals with null alleles for each of the previously identified or predicted glutamate-gated cation and anion channel subunits. Not surprisingly, given the array of ASH downstream synaptic partners, a number of the glutamate receptor mutants yielded phenotypes in various aspects of the modulated ASH mediated aversive responses. For example, the initiation of aversive responses in animals with null alleles for either avr-14 or glc-4, predicted to encode glutamate-gated Cl- channel subunits, was not stimulated by food or 5-HT, compared to wild type animals. In contrast, animals overexpressing either avr-14 or glc-4 initiated aversive response more rapidly than wild type animals off food. AVR-14 has been characterized extensively and encodes a homomeric glutamate-gated Cl- channel. In contrast, GLC-4 is the most distantly related of the predicted glutamate-gated Cl- channel subunits and has not been characterized. Therefore, GLC-4 was expressed heterologously in Xenopus oocytes to determine ligand-specificity and over the 100 ligands were examined. None activated a Cl- current in the oocytes. In contrast, GLC-4 expression with AVR-14 or AVR-15, well characterized glutamate-gated Cl- channel subunits, reduced peak Cl- currents and glutamate affinity, suggesting the GLC-4 interacted with these subunit to alter channel properties. This result appeared to be specific for glutamate-gated Cl- channels, as GLC-4 co-expression with MOD-1 that forms a 5-HT dependent Cl- channel had no effect on MOD-1 signaling. These studies are continuing to localize AVR-14 and GLC-4 in the ASH-mediated locomotory circuit at both the cellular and subcellular levels to determine their roles in ASH signaling and, more importantly, to determine if they associate in vivo.

Mulcahy B et al. (2010) Invert Neurosci "Meeting report: 2010 Caenorhabditis elegans Neurobiology Meeting, University of Wisconsin, USA."

Mulcahy B, Ient B

[Invert Neurosci, 2010]

Against the backdrop of the scenic Lake Mendota, the C. elegans Neurobiology Meeting came to a head. Expertly organised by Brian Ackley and Bruce Bamber and hosted at the accommodating University of Wisconsin, the meeting brought together recent contributions from many of the major research groups working on the neurobiology of C. elegans. With seven keynote speakers, 57 verbal presentations and hundreds of posters, this exciting event spanned a fascinating 3days from 27 June to 30 June 2010. In keeping with the tradition of this conference, the event on the whole was spearheaded by young investigators from several research institutions. The meeting served to emphasise the gains enjoyed by taking advantage of the genetic tractability of the worm. A thread that ran through the meeting was the importance of integrating data across different levels of biological organisation to permit delineation of the physiology underpinning discrete behavioural states. Recent advances in optogenetics and microfluidics were at the forefront of refining these analyses. The presentations discussed in this meeting report are a selection which reflects this overarching theme.