Pierce-Shimomura, Jonathan T. et al. (2011) International Worm Meeting "Serotonergic blockade prevents age-related neurodegeneration in C. elegans model of Alzheimer's disease."

Pierce-Shimomura, Jonathan T., Crisp, Ashley

[International Worm Meeting, 2011]

Alzheimer's disease (AD) is characterized by the selective degeneration of cholinergic neurons involved in memory. Although the precise etiology of AD remains unclear, the amyloid-precusor protein (APP) appears to be a causal agent for two main reasons. First, overexpression of APP or mutations in APP predict early-onset AD in humans. Second, dying neurons are surrounded by plaques composed of APP peptide fragments. With the simple architecture and ease of molecular manipulation of C. elegans, we explored the mechanisms of neurodegeneration caused by APP. The Li lab has previously found that overexpression of multiple copies of the APP-related gene called apl-1 leads to lethality and vacuolization in C. elegans (Hornsten et al., PNAS 2007). We have now found that, as in human AD, overexpression of a single wild-type copy of apl-1 or human APP result in age-related degeneration of a specific subset of cholinergic neurons in C. elegans. Deficits in two natural behaviors, swimming and egg-laying, correlate with the accumulation of APP protein specifically in these neurons and their eventual death. In addition, through genetic and pharmacological analyses, we have found that serotonergic signaling is both necessary and sufficient for degeneration of these neurons. Our results suggest that therapeutics designed to decrease serotonergic signaling may alleviate the pathology in mouse models of AD and perhaps even in patients with AD.

Jonathan T Pierce-Shimomura et al. (2003) International Worm Meeting "Ethanol intoxication in C. elegans results from activation of a BK potassium channel"

Tod R Thiele, Steven L McIntire, Cornelia I Bargmann, Miri K VanHoven, Andrew G Davies, Antonello Bonci, Hongkyun Kim, Jonathan T Pierce-Shimomura

[International Worm Meeting, 2003]

The fundamental mechanism responsible for the intoxicating effects of ethanol is unclear. Ethanol has been reported to alter the function of over 20 different membrane proteins in vitro; whether any of these changes relate to the intoxicating properties of ethanol is unknown. Ethanol has intoxicating effects on C. elegans including dose-dependent inhibition of locomotory and egg-laying behaviors. Although high exogenous concentrations of ethanol are required to induce behavioral responses, the tissue concentration in intoxicated animals is the same (20-30 mM) as that required to produce intoxication in mammals. To identify the neuronal proteins mediating the behavioral responses to ethanol, we carried out two independent genetic screens for mutants that are resistant to the inhibitory effects of ethanol on locomotion or egg laying. Only mutations in the slo-1 gene were found to produce a strong level of resistance to ethanol for each behavioral effect. slo-1 encodes a calcium-activated potassium (BK) channel (Wang et al. Neuron 2001).Neuronal expression of a slo-1(+) construct is sufficient to restore ethanol sensitivity to a slo-1 null mutant, suggesting that ethanol is acting on the nervous system to cause behavioral depression. We tested the possibility that ethanol mediates its effects through the SLO-1 potassium channel by performing electrophysiology of identified neurons in C. elegans. Ethanol, at physiological concentrations, reversibly increases the activity of currents mediated by the native SLO-1 channel. In single channel recordings, ethanol increases the probability of channel opening. These effects were absent in recordings from the neurons of slo-1 mutants. To independently demonstrate that activation of SLO-1 channels can lead to similar behavioral effects as those observed with ethanol treatment, we examined two semi-dominant alleles of slo-1 (ky389 and ky399) that were identified in a screen for animals with neuronal symmetry (Nsy) mutant phenotypes. Neuronal recordings from these two mutants reveals an increased frequency of SLO-1 channel opening, confirming that the mutant channels are more active than the wild-type channel. Both mutants display significantly reduced average speeds and egg laying frequencies. These data confirm that activation of the SLO-1 channel leads to a depression in the rates of locomotion and egg laying. Activation of BK channels may represent a fundamental mechanism by which ethanol causes intoxication in C. elegans and other systems.

Russell, Josh et al. (2013) International Worm Meeting "Humidity sensation requires a conserved DEG/ENaC complex in multi-dendritic FLP neurons."

Pierce-Shimomura, Jonathan, Russell, Josh

[International Worm Meeting, 2013]

Moisture is essential for life. Thus, it is surprising that the molecular basis for how most animals, including humans, sense humidity levels (hygrosensation) is unknown. Through development of a novel assay we discovered that C. elegans is exquisitely sensitive to humidity gradients as shallow as 0.03% relative humidity per 1 mm. A series of control experiments demonstrated that the worm detects changes in moisture in the air rather than cues specific to the assay apparatus. Next, by analyzing mutants we found several genes that may encode a conserved complex of mechanosensitive DEG/ENaC channels required for hygrosensation. Finally, though cell-specific ablation and rescue studies we have determined that hygrosensation requires the mechanosensitive neuron pair FLP, but not other mechanosensory neurons. FLP is unique for its extensive dendritic branching just beneath the cuticle in the head. These findings raise the possibility that humidity levels may be encoded by the extent to which the FLP dendritic field is stretched by local skin hydration. Clear orthologs of this mechanosensitive complex have also been identified in the multi-dendritic mechanosensory neurons in mouse and human those also terminate just below the epidermis. The similar receptive fields, morphology and mechanosensitive functions of these mammalian neurons to FLP neurons suggests C. elegans may help uncover the molecular basis for this elusive sensory modality in other animals including humans.

Guzman, Dawn et al. (2015) International Worm Meeting "Elucidating conserved neural mechanisms underlying defective motor pattern transitions."

Guzman, Dawn, Pierce-Shimomura, Jonathan

[International Worm Meeting, 2015]

For many animals, the ability efficiently navigate through their natural environments by using different forms of locomotion is critical for various aspects of survival - such as predator evasion and food seeking. Common forms of motion -such as swimming, walking, crawling or running - are governed by distinct rhythmic neural outputs. Dopamine has been found to play a conserved role in switching between such motor programs in a variety of species. One such example of this in humans can be seen in Parkinson's disease (PD) patients. Humans with PD lose the ability to initiate or switch between movements as a subset of their dopamine neurons degenerate. Our lab has recently demonstrated that C. elegans displays two distinct forms of locomotion - crawling and swimming - and that dopamine is necessary and sufficient for the transition from swimming to crawling. Despite this knowledge, it remains unknown how motor transition dysfunction may be overcome in the absence of dopamine. We are addressing this issue with two approaches that take advantage of the powerful genetics of C. elegans. First, we are conducting an unbiased forward genetic screen for novel mutations that suppress the swim-to-crawl transition defect of the dopamine deficient mutant cat-2. This gene encodes the dopamine synthesizing enzyme tyrosine hydroxylase conserved in all animals including humans. Mapping and cloning genes that can be mutated to enable locomotor transitions in the absence of dopamine may reveal insight into repair of dopamine-deficient circuitry in higher animals. Second, we are testing the hypothesis that an imbalance in the dopamine-serotonin ratio contributes to motor transition defects. We will test this hypothesis in the cat-2 mutant by impairing specific serotonergic pathways via mutation and pharmacological agents. If our hypothesis is correct, induced serotonin deficiency should restore normal motor transitions in the cat-2 mutant. Repair of motor transition deficits with strategies that do not rely on the presence of intact dopamine signaling is important because current treatments for Parkinson's disease only depend on boosting the signal of residual dopamine neurons (e.g. L-dopa & deep brain stimulation) and fail once dopamine neurons are depleted. .

Topper, Stephen M. et al. (2013) International Worm Meeting "Dopaminergic control of gait switching in C. elegans."

Pierce-Shimomura, Jonathan, Aguilar, Sara, Topper, Stephen M., Young, Layla

[International Worm Meeting, 2013]

The ability to switch between different forms of locomotion is critical to many aspects of survival, whether it is switching from walking to running to evade predators, or switching to a slower gait to obtain food. However, the neuronal mechanisms of gait switching are not well understood. We recently showed C. elegans, displays distinct crawl and swim gaits, mediated by dopamine and serotonin, respectively (Vidal-Gadea et al., 2011). Further investigation into the role of dopamine signaling in the transition to crawl has indicated the D1-like dopamine receptor dop-4 as a key component. Laser microablation of dop-4-expressing neurons has revealed single neurons that are required for the transition to crawl. Optogenetic activation of dop-4-expressing neurons via the light-activated GPCR optoXRB2 induces crawl-like behavior in swimming worms. Finally, expression of dop-4 in specific subsets of dop-4 neurons is sufficient to rescue the swim to crawl transition. We are now combining noninvasive imaging of these neurons in freely moving worms with optogenetics to dissect how dopamine controls gait switching at the circuit level. A genetic analysis dopaminergic locomotory in C. elegans may reveal fundamental principles on gait switching with implications for many fields, including the study of human ailments such as Parkinson's disease.

Vidal-Gadea, Andres G. et al. (2013) International Worm Meeting "Magnetotaxis in C. elegans."

Vidal-Gadea, Andres G., Pierce-Shimomura, Jonathan T., Ward, Kristi A.

[International Worm Meeting, 2013]

The magnetic field of the Earth provides an ancient and continuous source of directional information to organisms able to detect it. While the last half-century has seen the list of species capable of this feat grow steadily (from bacteria to mammals), the mechanisms by which magentosensation is accomplished in animals has remained elusive. Magnetotactic bacteria are known to harvest iron from their environment to build nanometer-sized "compasses" and evidence of magnetite has been reported in many magnetotactic animals. It remains unclear whether and how these putative "biological compasses" are used. This is partly due to the fact that a magnetosensory neuron has never been identified in any animal. We show that the nematode C. elegans readily orients to common magnets in addition to the Earth's magnetic field. Using a custom-built magnetic cage, we tested worms in magnetic fields controlled along three dimensions. Worms migrated at an angle to the field, in what would be the "down" direction. Our findings suggests that the Earth's magnetic field may serve as a better cue than gravity for these tiny animals to orient while burrowing. Through behavioral analysis of mutants as well as cell-specific rescue and ablation, we next identified a pair of amphid sensory neurons as necessary and sufficient to mediate magnetotaxis in C. elegans. Functional calcium imaging performed on these neurons revealed calcium transients induced by magnetic fields. Genes and neurons required for magnetotaxis are distinct from those previously reported to be essential for electrotaxis. Magnetic orientation in C. elegans appears to take place through a light-independent mechanism, and to rely on a cGMP-dependent transduction pathway. To our knowledge, this represents the first report of sensory neurons required for magnetic orientation in any species.

Vidal-Gadea, Andres et al. (2015) International Worm Meeting "Geographical tuning in magnetotactic response across C. elegans wild-type isolates."

Ward, Kristi, Beron, Celia, Vidal-Gadea, Andres, Pierce-Shimomura, Jonathan

[International Worm Meeting, 2015]

Rotation of the earth's liquid core generates a magnetic field used by many organisms to navigate their environment. While some animals such as turtles and birds use the magnetic field to engage in horizontal migrations, other organisms like magnetotactic bacteria use it to guide their migrations vertically. We find that C. elegans readily orients to artificial magnetic fields of earth strength. When assaying responses to the natural magnetic field of the earth, we found that worms appear to use the geomagnetic field to guide vertical migrations via an identified a pair of sensory neurons. Because the orientation of the geomagnetic field differs across the globe, we tested the magnetotactic ability and migratory preference of the standard lab strain (N2), and of wild-type strains isolated from different locations across the planet. We found that different populations displayed an innate preference to migrate at an angle to magnetic fields of earth-strength that would optimize their UP or DOWN direction when burrowing in their native global location. For instance, in England the geomagnetic field pierces the earth at +66 degrees (north points down). We found that well-fed British N2 worms prefer to migrate 120 degrees to an earth-strength artificial magnetic field. This seemingly arbitrary angle corresponds to the optimal angle to orient them upward when burrowing in England. By contrast, starved N2 worms migrated in the opposite direction (i.e. 300 degrees to the field), which would orient them downward in England. Consistent with natural populations adapting to local magnetic fields, we next found that worms isolated from Australia, where the geomagnetic field emanates out of the earth at -66 degrees (north points up), displayed an opposite innate pattern of migratory preference. Similar results were found for wild-type worms from Hawaii. This pattern of optimal natural variation in magnetic orientation in C. elegans serves as an excellent example to relate spatiotemporal genetic variation with a behavioral trait. The breath in number and distribution of wild-type C. elegans populations makes this a promising model for studying the effects of natural and artificial magnetic field variation on the behavior of a genetically tractable animal.

Sreekanth Chalasani et al. (2007) International Worm Meeting "Functional analysis of a neural circuit controlling turning behavior in Caenorhabditis elegans."

Cornelia Bargmann, Jesse Gray, Makoto Tsunozaki, Sreekanth Chalasani, Nikolas Chronis

[International Worm Meeting, 2007]

C. elegans increase its frequency of reversals and turns (jointly termed pirouettes, Pierce-Shimomura et al 1999) after removal of a food stimulus. The AWC and ASK sensory neurons and the AIB interneurons stimulate pirouettes immediately after removal from food, while the AIY and AIA interneurons inhibit pirouettes (Wakabayashi et al 2004, Gray et al 2005). We have found that the sensory neuron AWC releases two neurotransmitters (glutamate and a neuropeptide, NLP-1) when the worm is removed from food. The released glutamate acts to activate AIB and inhibit AIY, promoting reversals. Strains with different reversal frequencies can be generated by manipulating the level of glutamate receptors on interneurons AIB and AIY. Decreasing receptor expression leads to fewer reversals, and increasing receptor expression results in more reversals than in wild-type. The AWC released neuropeptide NLP-1 serves to reduce reversals, suggesting that reversal frequencies are regulated by at least two opposing signaling systems. Consistent with behavioral responses, AWC and AIB respond (by increasing calcium concentration) to removal of stimulus. We plan to extend the imaging studies to other neurons in the circuit. These results provide a plausible molecular explanation that links neurotransmitters, their receptors, and neuronal circuitry to generate behavior. References: Gray, J.M., Hill, J.J., and Bargmann, C.I. (2005). A circuit for navigation in Caenorhabditis elegans. Proc. Natl. Acad. Sci. 102, 3184-3191. Pierce-Shimomura, J.T., Morse, T.M., and Lockery, S.R. (1999). The fundamental role of pirouettes in Caenorhabditis elegans chemotaxis. J. Neurosci 19, 9557-9569. Wakabayashi, T., Kitagawa, I., and Shingai, R. (2004). Neurons regulating the duration of forward locomotion in Caenorhabditis elegans. Neurosci. Res. 50, 103-111.

Vidal-Gadea, Andres et al. (2015) International Worm Meeting "Burrowing behavior of C. elegans used to study neuromuscular disorder models."

Vidal-Gadea, Andres, Parikh, Adhishri, Pierce-Shimomura, Jonathan, Cohn, Jesse, Hwang, Grace, Beron, Celia

[International Worm Meeting, 2015]

The nematode Caenorhabditis elegans is a powerful model system for the study of human neuromuscular function and disorders. However, many worm models of human disease only show mild crawling phenotypes. In their natural habitat, C. elegans likely spends much of the time burrowing through the soil matrix. We developed a burrowing assay to challenge motor output by placing worms in agar-filled pipettes of increasing densities. We find that burrowing involves distinct kinematics and turning strategies from crawling that vary with the properties of the substrate. We show that Duchenne muscular dystrophy model (dys-1) mutants crawl normally but are severely impaired in burrowing. In stark contrast with wild-type, muscular degeneration in the dys-1 mutant is hastened and exacerbated by burrowing. We performed a genetic screen and isolated several suppressor mutants with proficient burrowing in a dys-1 mutant background. Further study of burrowing in C. elegans will enhance the study of diseases affecting neuromuscular integrity, and provide insights into the natural behavior of this and other nematodes.

Topper, Stephen M. et al. (2013) International Worm Meeting "Ethanol induces state-dependent behavioral transition."

Vidal-Gadea, Andres, Pierce-Shimomura, Jonathan, Topper, Stephen M., Aguilar, Sara, Young, Layla

[International Worm Meeting, 2013]

Alcohol, the most widely abused drug in the world, has a wide range of effect on individuals and there are many factors that predispose one to addiction. Chief among them are stress, depression, and anxiety, all of which include altered monoamine signaling. It remains unclear how behavioral states differentially influence responses to ethanol. C. elegans displays distinct behavioral states associated with locomotion (crawling and swimming) that are mediated by dopamine and serotonin respectively. We found that ethanol-induced responses in C. elegans depended on crawl or swim behavioral state. Whereas alcohol non-specifically impaired locomotion and feeding in crawling worms on land, alcohol induced a specific transition from swim to crawl state in worms submerged in ethanol. This response was dependent on dopamine. Loss of the D1-like dopamine receptor DOP-4 impaired the EtOH-induced transition to crawl, while optogenetic inhibition of DOP-4 receptor-expressing neurons via the Arch chloride pump recovered the swim state. These results suggest that alterations of dopamine-dependent behavioral states can drastically influence EtOH-induced behaviors with implications for prevention of addiction. Acknowledgements: CGC and the Knockout Consortium for strains, Bruce/Jones Award for Alcohol and Addiction Research, Karl Deisseroff for reagents.