Light and Hydrogen Peroxide Inhibit C. elegans Feeding through Gustatory Receptor Orthologs and Pharyngeal Neurons

While gustatory sensing of the five primary flavors (sweet, salty, sour, bitter, and savory) has been extensively studied, pathways that detect non-canonical taste stimuli remain relatively unexplored. In particular, while reactive oxygen species cause generalized damage to biological systems, no gustatory mechanism to prevent ingestion of such material has been identified in any organism. We observed that light inhibits C. elegans feeding and used light as a tool to uncover molecular and neural mechanisms for gustation. Light can generate hydrogen peroxide, and we discovered that hydrogen peroxide similarly inhibits feeding. The gustatory receptor family members LITE-1 and GUR-3 are required for the inhibition of feeding by light and hydrogen peroxide. The I2 pharyngeal neurons increase calcium in response to light and hydrogen peroxide, and these responses require GUR-3 and a conserved antioxidant enzyme peroxiredoxin PRDX-2. Our results demonstrate a gustatory mechanism that mediates the detection and blocks ingestion of a noncanonical taste stimulus, hydrogen peroxide.National Science Foundation (U.S.). Graduate Research Fellowship ProgramNational Institutes of Health (U.S.) (Grant GM24663

The CDK8 Complex and Proneural Proteins Together Drive Neurogenesis from a Mesodermal Lineage

© 2017 Elsevier Ltd At least some animal species can generate neurons from mesoderm or endoderm, but the underlying mechanisms remain unknown. We screened for C. elegans mutants in which the presumptive mesoderm-derived I4 neuron adopts a muscle-like cell fate. From this screen, we identified HLH-3, the C. elegans homolog of a mammalian proneural protein (Ascl1) used for in vitro neuronal reprogramming, as required for efficient I4 neurogenesis. We discovered that the CDK-8 Mediator kinase module acts together with a second proneural protein, HLH-2, and in parallel to HLH-3 to promote I4 neurogenesis. Genetic analysis revealed that CDK-8 most likely promotes I4 neurogenesis by inhibiting the CDK-7/CYH-1 (CDK7/cyclin H) kinase module of the transcription initiation factor TFIIH. Ectopic expression of HLH-2 and HLH-3 together promoted expression of neuronal features in non-neuronal cells. These findings reveal that the Mediator CDK8 kinase module can promote non-ectodermal neurogenesis and suggest that inhibiting CDK7/cyclin H might similarly promote neurogenesis.National Institutes of Health (U.S.). Intramural Research Program (P40 OD010440)National Institutes of Health (U.S.) (GM24663)National Institutes of Health (U.S.) (HD75076

Ligand-Gated Chloride Channels Are Receptors for Biogenic Amines in C. elegans

Biogenic amines such as serotonin and dopamine are intercellular signaling molecules that function widely as neurotransmitters and neuromodulators. We have identified in the nematode Caenorhabditis elegans three ligand-gated chloride channels that are receptors for biogenic amines: LGC-53 is a high-affinity dopamine receptor, LGC-55 is a high-affinity tyramine receptor, and LGC-40 is a low-affinity serotonin receptor that is also gated by choline and acetylcholine. lgc-55 mutants are defective in a behavior that requires endogenous tyramine, which indicates that this ionotropic tyramine receptor functions in tyramine signaling in vivo. Our studies suggest that direct activation of membrane chloride conductances is a general mechanism of action for biogenic amines in the modulation of C. elegans behavior.National Institutes of Health (U.S.) (Grant GM24663)Howard Hughes Medical InstituteLife Sciences Research FoundationMedical Foundation, Inc

Distinct Neural Circuits Control Rhythm Inhibition and Spitting by the Myogenic Pharynx of C. elegans

Neural circuits have long been known to modulate myogenic muscles such as the heart, yet a mechanistic understanding at the cellular and molecular levels remains limited. We studied how light inhibits pumping of the Caenorhabditis elegans pharynx, a myogenic muscular pump for feeding, and found three neural circuits that alter pumping. First, light inhibits pumping via the I2 neuron monosynaptic circuit. Our electron microscopic reconstruction of the anterior pharynx revealed evidence for synapses from I2 onto muscle that were missing from the published connectome, and we show that these “missed synapses” are likely functional. Second, light inhibits pumping through the RIP-I1-MC neuron polysynaptic circuit, in which an inhibitory signal is likely transmitted from outside the pharynx into the pharynx in a manner analogous to how the mammalian autonomic nervous system controls the heart. Third, light causes a novel pharyngeal behavior, reversal of flow or “spitting,” which is induced by the M1 neuron. These three neural circuits show that neurons can control a myogenic muscle organ not only by changing the contraction rate but also by altering the functional consequences of the contraction itself, transforming swallowing into spitting. Our observations also illustrate why connectome builders and users should be cognizant that functional synaptic connections might exist despite the absence of a declared synapse in the connectome.United States. National Institutes of Health (GM24663

Presumptive TRP channel CED-11 promotes cell volume decrease and facilitates degradation of apoptotic cells in

Apoptotic cells undergo a series of morphological changes. These changes are dependent on caspase cleavage of downstream targets, but which targets are signifi cant and how they facilitate the death process are not well understood. In Caenorhabditis elegans an increase in the refractility of the dying cell is a hallmark morphological change that is caspase dependent. We identify a presumptive transient receptor potential (TRP) cation channel, CED-11, that acts in the dying cell to promote the increase in apoptotic cell refractility. CED-11 is required for multiple other morphological changes during apoptosis, including an increase in electron density as visualized by electron microscopy and a decrease in cell volume. In ced-11 mutants, the degradation of apoptotic cells is delayed. Mutation of ced-11 does not cause an increase in cell survival but can enhance cell survival in other cell-death mutants, indicating that ced-11 facilitates the death process. In short, ced-11 acts downstream of caspase activation to promote the shrinkage, death, and degradation of apoptotic cells. Keywords: TRP channel; apoptosis; C. elegans; cell volume; apoptotic volume decreaseNational Institutes of Health (U.S.) (Grant T32GM007287

Neurohormonal signaling via a sulfotransferase antagonizes insulin-like signaling to regulate a Caenorhabditis elegans stress response

Insulin and insulin-like signaling regulates a broad spectrum of growth and metabolic responses to a variety of internal and environmental stimuli. For example, the inhibition of insulin-like signaling in C. elegans mediates its response to both osmotic stress and starvation. We report that in response to osmotic stress the cytosolic sulfotransferase SSU-1 antagonizes insulin-like signaling and promotes developmental arrest. Both SSU-1 and the DAF-16 FOXO transcription factor, which is activated when insulin signaling is low, are needed to drive specific responses to reduced insulin-like signaling. We demonstrate that SSU-1 functions in a single pair of sensory neurons to control intercellular signaling via the nuclear hormone receptor NHR-1 and promote both the specific transcriptional response to osmotic stress and altered lysophosphatidylcholine metabolism. Our results show the requirement of a sulfotransferase–nuclear hormone receptor neurohormonal signaling pathway for some but not all consequences of reduced insulin-like signaling.National Center for Research Resources (U.S.)National Institutes of Health (U.S.) (grant GM024663)National Science Foundation (U.S.) (grant 1122374)University of Cambridge. Centre for Trophoblast Research (Next Generation Fellowship)National Institutes of Health (U.S.) (grant GM117408

The Conserved VPS-50 Protein Functions in Dense-Core Vesicle Maturation and Acidification and Controls Animal Behavior

The modification of behavior in response to experience is crucial for animals to adapt to environmental changes. Although factors such as neuropeptides and hormones are known to function in the switch between alternative behavioral states, the mechanisms by which these factors transduce, store, retrieve, and integrate environmental signals to regulate behavior are poorly understood. The rate of locomotion of the nematode Caenorhabditis elegans depends on both current and past food availability. Specifically, C. elegans slows its locomotion when it encounters food, and animals in a food-deprived state slow even more than animals in a well-fed state. The slowing responses of well-fed and food-deprived animals in the presence of food represent distinct behavioral states, as they are controlled by different sets of genes, neurotransmitters, and neurons. Here we describe an evolutionarily conserved C. elegans protein, VPS-50, that is required for animals to assume the well-fed behavioral state. Both VPS-50 and its murine homolog mVPS50 are expressed in neurons, are associated with synaptic and dense-core vesicles, and control vesicle acidification and hence synaptic function, likely through regulation of the assembly of the V-ATPase complex. We propose that dense-core vesicle acidification controlled by the evolutionarily conserved protein VPS-50/mVPS50 affects behavioral state by modulating neuropeptide levels and presynaptic neuronal function in both C. elegans and mammals.National Institutes of Health (U.S.) (Grant GM024663

Acyl-CoA Dehydrogenase Drives Heat Adaptation by Sequestering Fatty Acids

Cells adapt to temperature shifts by adjusting levels of lipid desaturation and membrane fluidity. This fundamental process occurs in nearly all forms of life, but its mechanism in eukaryotes is unknown. We discovered that the evolutionarily conserved C. elegans gene acdh-11 (acyl CoAdehydrogenase, ACDH) facilitates heat adaptation by regulating the lipid desaturase FAT-7. Human ACDH deficiency causes the most common inherited disorders of fatty acid oxidation, with syndromes that are exacerbated by hyperthermia. Heat up-regulates acdh-11 expression to decrease fat-7 expression. We solved the high-resolution crystal structure of ACDH-11 and established the molecular basis of its selective and high-affinity binding to C11/C12-chain fatty acids. ACDH-11 sequesters C11/C12-chain fatty acids and prevents these fatty acids from activating nuclear hormone receptors and driving fat-7 expression. Thus, the ACDH-11 pathway drives heat adaptation by linking temperature shifts to regulation of lipid desaturase levels and membrane fluidity via an unprecedented mode of fatty acid signaling.National Institutes of Health (U.S.) (Grants GM24663 and K99HL11665)Charles A. King Trust (Postdoctoral Fellowship

A C9orf72 ALS/FTD Ortholog Acts in Endolysosomal Degradation and Lysosomal Homeostasis

The most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) is the expansion of a hexanucleotide repeat in a non-coding region of the gene C9orf72. We report that loss-of-function mutations in alfa-1, the Caenorhabditis elegans ortholog of C9orf72, cause a novel phenotypic defect: endocytosed yolk is abnormally released into the extra-embryonic space, resulting in refractile “blobs.” The alfa-1 blob phenotype is partially rescued by the expression of the human C9orf72 protein, demonstrating that C9orf72 and alfa-1 function similarly. We show that alfa-1 and R144.5, which we identified from a genetic screen for mutants with the blob phenotype and renamed smcr-8, act in the degradation of endolysosomal content and subsequent lysosome reformation. The alfa-1 abnormality in lysosomal reformation results in a general dysregulation in lysosomal homeostasis, leading to defective degradation of phagosomal and autophagosomal contents. We suggest that, like alfa-1, C9orf72 functions in the degradation of endocytosed material and in the maintenance of lysosomal homeostasis. This previously undescribed function of C9orf72 explains a variety of disparate observations concerning the effects of mutations in C9orf72 and its homologs, including the abnormal accumulation of lysosomes and defective fusion of lysosomes to phagosomes. We suggest that aspects of the pathogenic and clinical features of ALS/FTD caused by C9orf72 mutations, such as altered immune responses, aggregation of autophagy targets, and excessive neuronal excitation, result from a reduction in C9orf72 gene function and consequent abnormalities in lysosomal degradation. Corrionero and Horvitz show that the C. elegans gene alfa-1 functions in the degradation of endocytosed material and hence has effects on subsequent lysosomal reformation and lysosomal homeostasis maintenance. Human C9orf72 functions similarly. Aspects of ALS/FTD might result from decreased C9orf72 function and defective lysosomal degradation

Hypoxia-inducible factor cell non-autonomously regulates C. elegans stress responses and behavior via a nuclear receptor

The HIF (hypoxia-inducible factor) transcription factor is the master regulator of the metazoan response to chronic hypoxia. In addition to promoting adaptations to low oxygen, HIF drives cytoprotective mechanisms in response to stresses and modulates neural circuit function. How most HIF targets act in the control of the diverse aspects of HIF-regulated biology remains unknown. We discovered that a HIF target, the C. elegans gene cyp-36A1, is required for numerous HIF-dependent processes, including modulation of gene expression, stress resistance, and behavior. cyp-36A1encodes a cytochrome P450 enzyme that we show controls expression of more than a third of HIF-induced genes. CYP-36A1 acts cell non-autonomously by regulating the activity of the nuclear hormone receptor NHR-46, suggesting that CYP-36A1 functions as a biosynthetic enzyme for a hormone ligand of this receptor. We propose that regulation of HIF effectors through activation of cytochrome P450 enzyme/nuclear receptor signaling pathways could similarly occur in humans.National Institutes of Health (Grant GM024663)National Institutes of Health (Grant T32GM007287