A Specific Subset of Transient Receptor Potential Vanilloid-Type Channel Subunits in Caenorhabditis elegans Endocrine Cells Function as Mixed Heteromers to Promote Neurotransmitter Release

Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA.
Genetics (Impact Factor: 5.96). 02/2007; 175(1):93-105. DOI: 10.1534/genetics.106.065516
Source: PubMed


Transient receptor potential (TRP) channel subunits form homotetramers that function in sensory transduction. Heteromeric channels also form, but their physiological subunit compositions and functions are largely unknown. We found a dominant-negative mutant of the C. elegans TRPV (vanilloid-type) subunit OCR-2 that apparently incorporates into and inactivates OCR-2 homomers as well as heteromers with the TRPV subunits OCR-1 and -4, resulting in a premature egg-laying defect. This defect is reproduced by knocking out all three OCR genes, but not by any single knockout. Thus a mixture of redundant heteromeric channels prevents premature egg laying. These channels, as well as the G-protein G alpha(o), function in neuroendocrine cells to promote release of neurotransmitters that block egg laying until eggs filling the uterus deform the neuroendocrine cells. The TRPV channel OSM-9, previously suggested to be an obligate heteromeric partner of OCR-2 in sensory neurons, is expressed in the neuroendocrine cells but has no detectable role in egg laying. Our results identify a specific set of heteromeric TRPV channels that redundantly regulate neuroendocrine function and show that a subunit combination that functions in sensory neurons is also present in neuroendocrine cells but has no detectable function in these cells.

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    • "mkate2 encodes a far-red fluorescent protein [38] and was codon-optimized for expression in C. elegans using codon adapter [39]. The tagging was done according to an established strategy into an internal loop of the G protein [40]. The insertion site was analogous to that of a published, functional gfp-tagged goa-1 transgene [41]. "
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    ABSTRACT: Sleep-like states are characterized by massively reduced behavioral activity. Little is known about genetic control of sleep-like behavior. It is also not clear how general activity levels during wake-like behavior influence activity levels during sleep-like behavior. Mutations that increase wake-like activity are generally believed to also increase activity during sleep-like behavior and mutations that decrease wake-like activity are believed to have decreased activity during sleep-like behavior. We studied sleep-like behavior during lethargus in larvae of Caenorhabditis elegans. We looked through a small set of known mutants with altered activity levels. As expected, mutants with increased activity levels typically showed less sleep-like behavior. Among these hyperactive mutants was a gain-of-function mutant of the conserved heterotrimeric G protein subunit Galphaq gene egl-30. We found, however, that an unusual semidominant hypoactive mutant of egl-30 also had reduced sleep-like behavior. While movement was severely reduced and impaired in the semidominant egl-30 mutant, sleep-like behavior was severely reduced: the semidominant egl-30 mutant lacked prolonged periods of complete immobility, reduced spontaneous neural activity less, and reduced responsiveness to stimulation less. egl-30 is a well-known regulator of behavior. Our results suggest that egl-30 controls not only general activity levels, but also differences between wake-like and sleep-like behavior.
    PLoS ONE 09/2013; 8(9):e75853. DOI:10.1371/journal.pone.0075853 · 3.23 Impact Factor
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    • "OCR-2 and OSM-9 are homologues of the mammalian TRPV channel genes in C. elegans, and are coexpressed in sensory neurons [34]. Both are expressed in PVD [35-37]. Our results suggest that ocr-2 is required for noxious heat sensation at the midbody, but osm-9 is not (Figure 8b). "
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    ABSTRACT: Nociception evokes a rapid withdrawal behavior designed to protect the animal from potential danger. C. elegans performs a reflexive reversal or forward locomotory response when presented with noxious stimuli at the head or tail, respectively. Here, we have developed an assay with precise spatial and temporal control of an infrared laser stimulus that targets one-fifth of the worm's body and quantifies multiple aspects of the worm's escape response. When stimulated at the head, we found that the escape response can be elicited by changes in temperature as small as a fraction of a degree Celsius, and that aspects of the escape behavior such as the response latency and the escape direction change advantageously as the amplitude of the noxious stimulus increases. We have mapped the behavioral receptive field of thermal nociception along the entire body of the worm, and show a midbody avoidance behavior distinct from the head and tail responses. At the midbody, the worm is sensitive to a change in the stimulus location as small as 80 mum. This midbody response is probabilistic, producing either a backward, forward or pause state after the stimulus. The distribution of these states shifts from reverse-biased to forward-biased as the location of the stimulus moves from the middle towards the anterior or posterior of the worm, respectively. We identified PVD as the thermal nociceptor for the midbody response using calcium imaging, genetic ablation and laser ablation. Analyses of mutants suggest the possibility that TRPV channels and glutamate are involved in facilitating the midbody noxious response. Through high resolution quantitative behavioral analysis, we have comprehensively characterized the C. elegans escape response to noxious thermal stimuli applied along its body, and found a novel midbody response. We further identified the nociceptor PVD as required to sense noxious heat at the midbody and can spatially differentiate localized thermal stimuli.
    BMC Neuroscience 07/2013; 14(1):66. DOI:10.1186/1471-2202-14-66 · 2.67 Impact Factor
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    • "Both the ocr-2 and osm-9 genes are expressed in PHC and at least osm-9 is expressed in the FLP sensory neurons but not in AFD [15], [32]. We next asked whether expression of ocr-2 and osm-9 in FLP and PHC is sufficient for rescuing the defective Tav response in the mutant. "
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    ABSTRACT: Any organism depends on its ability to sense temperature and avoid noxious heat. The nematode Caenorhabditis elegans responds to noxious temperatures exceeding ∼35°C and also senses changes in its environmental temperature in the range between 15 and 25°C. The neural circuits and molecular mechanisms involved in thermotaxis have been successfully studied, whereas details of the thermal avoidance behavior remain elusive. In this work, we investigate neurological and molecular aspects of thermonociception using genetic, cell biological and physiological approaches. We show here that the thermosensory neurons AFD, in addition to sensing temperature within the range within which the animals can thrive, also contribute to the sensation of noxious temperatures resulting in a reflex-like escape reaction. Distinct sets of interneurons are involved in transmitting thermonociception and thermotaxis, respectively. Loss of AFD is partially compensated by the activity of a pair of multidendritic, polymodal neurons, FLP, whereas laser ablation of both types of neurons abrogated the heat response in the head of the animals almost completely. A third pair of heat sensory neurons, PHC, is situated in the tail. We find that the thermal avoidance response requires the cell autonomous function of cGMP dependent Cyclic Nucleotide-Gated (CNG) channels in AFD, and the heat- and capsaicin-sensitive Transient Receptor Potential Vanilloid (TRPV) channels in the FLP and PHC sensory neurons. Our results identify distinct thermal responses mediated by a single neuron, but also show that parallel nociceptor circuits and molecules may be used as back-up strategies to guarantee fast and efficient responses to potentially detrimental stimuli.
    PLoS ONE 03/2012; 7(3):e32360. DOI:10.1371/journal.pone.0032360 · 3.23 Impact Factor
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