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Cell-Autonomous Gβ Signaling Defines Neuron-Specific Steady State Serotonin Synthesis in Caenorhabditis elegans.

Xu L, Choi S, Xie Y, Sze JY - PLoS Genet. (2015)

Bottom Line: We found that signaling through cell autonomous GPB-1 to the OCR-2 TRPV channel defines the baseline expression of 5-HT synthesis enzyme tryptophan hydroxylase tph-1 in ADF chemosensory neurons.These results revealed a Gβ-mediated signaling operating in differentiated cells to specify intrinsic functional properties, and indicate that baseline TPH expression is not a default generic serotonergic fate, but is programmed in a cell-specific manner in the mature nervous system.Cell-specific regulation of TPH expression could be a general principle for tailored steady state 5-HT synthesis in functionally distinct neurons and their regulation of innate behavior.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States of America.

ABSTRACT
Heterotrimeric G proteins regulate a vast array of cellular functions via specific intracellular effectors. Accumulating pharmacological and biochemical studies implicate Gβ subunits as signaling molecules interacting directly with a wide range of effectors to modulate downstream cellular responses, in addition to their role in regulating Gα subunit activities. However, the native biological roles of Gβ-mediated signaling pathways in vivo have been characterized only in a few cases. Here, we identified a Gβ GPB-1 signaling pathway operating in specific serotonergic neurons to the define steady state serotonin (5-HT) synthesis, through a genetic screen for 5-HT synthesis mutants in Caenorhabditis elegans. We found that signaling through cell autonomous GPB-1 to the OCR-2 TRPV channel defines the baseline expression of 5-HT synthesis enzyme tryptophan hydroxylase tph-1 in ADF chemosensory neurons. This Gβ signaling pathway is not essential for establishing the serotonergic cell fates and is mechanistically separated from stress-induced tph-1 upregulation. We identified that ADF-produced 5-HT controls specific innate rhythmic behaviors. These results revealed a Gβ-mediated signaling operating in differentiated cells to specify intrinsic functional properties, and indicate that baseline TPH expression is not a default generic serotonergic fate, but is programmed in a cell-specific manner in the mature nervous system. Cell-specific regulation of TPH expression could be a general principle for tailored steady state 5-HT synthesis in functionally distinct neurons and their regulation of innate behavior.

No MeSH data available.


Related in: MedlinePlus

tph-1::gfp expression in gpb-1(yz71) mutants under optimal and aversive conditions.(A) Dauer formation induced by aversive growth conditions caused ADF tph-1::gfp upregulation in WT and yz71mutants, as compared to their respective L4 stage siblings. (B) Mutation in cilia structural gene che-2 was capable of triggering ADF tph-1::gfp upregulation in yz71 mutants. (C) Pathogen PA14 failed to induce ADF tph-1::gfp upregulation in yz71 mutants, as comparing tph-1::gfp between 1st day adults fed PA14 and non-pathogenic bacterial control OP50 for 6 hr. gpb-1(g) transgene restored the PA14 response in yz71 mutants. (D) Comparing ADF tph-1::gfp between gpb-1(yz71) and ocr-2 TRPV channel mutants. In both mutants, ADF tph-1::gfp was diminished under optimal growth conditions, but enhanced in tir-1(yz68gf) background as compared to the yz71 and ocr-2 single mutants. yz71 and ocr-2 did not produce an additive effect. For each assay, the value of ADF GFP fluorescence in WT animals under a stress paradigm and that of mutants is normalized to the value of WT animals under optimal conditions. Data represent the average of ≥ 3 trials ± SEM, * p < 0.05, *** p < 0.001, t-test for two group comparisons, and ANOVA for multi-group/condition comparisons.
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pgen.1005540.g003: tph-1::gfp expression in gpb-1(yz71) mutants under optimal and aversive conditions.(A) Dauer formation induced by aversive growth conditions caused ADF tph-1::gfp upregulation in WT and yz71mutants, as compared to their respective L4 stage siblings. (B) Mutation in cilia structural gene che-2 was capable of triggering ADF tph-1::gfp upregulation in yz71 mutants. (C) Pathogen PA14 failed to induce ADF tph-1::gfp upregulation in yz71 mutants, as comparing tph-1::gfp between 1st day adults fed PA14 and non-pathogenic bacterial control OP50 for 6 hr. gpb-1(g) transgene restored the PA14 response in yz71 mutants. (D) Comparing ADF tph-1::gfp between gpb-1(yz71) and ocr-2 TRPV channel mutants. In both mutants, ADF tph-1::gfp was diminished under optimal growth conditions, but enhanced in tir-1(yz68gf) background as compared to the yz71 and ocr-2 single mutants. yz71 and ocr-2 did not produce an additive effect. For each assay, the value of ADF GFP fluorescence in WT animals under a stress paradigm and that of mutants is normalized to the value of WT animals under optimal conditions. Data represent the average of ≥ 3 trials ± SEM, * p < 0.05, *** p < 0.001, t-test for two group comparisons, and ANOVA for multi-group/condition comparisons.

Mentions: A stress-resistant state called dauer can be induced by a defined set of aversive growth conditions and is the most commonly used paradigm in C. elegans stress response studies [24]. Dauers enhance a battery of stress responsive genes to produce a series of physiological, morphological and behavioral remodeling [24]. Previously, we identified that alteration of ADF sensory cilia architecture caused either by dauer formation or genetic mutations in intraflagellar transport (IFT) triggers ADF tph-1 upregulation [10]. When yz71 mutants were induced to form dauers, ADF tph-1::gfp was significantly enhanced compared to their siblings under optimal growth conditions (Fig 3A). Likewise, we observed elevated ADF tph-1::gfp in yz71 mutants carrying defective IFT component che-2 (Fig 3B). However, ADF tph-1::gfp levels in yz71 dauers and yz71;che-2 double mutants were lower than WT dauers and che-2 single mutants, respectively (Fig 3A and 3B). These observations support the idea that dauer formation and GPB-1 regulate two mechanistically separable layers of tph-1 expression. yz71 mutants do not impair tph-1 upregulation induced by dauer formation or cilia structural alterations but have a lower baseline of tph-1 expression.


Cell-Autonomous Gβ Signaling Defines Neuron-Specific Steady State Serotonin Synthesis in Caenorhabditis elegans.

Xu L, Choi S, Xie Y, Sze JY - PLoS Genet. (2015)

tph-1::gfp expression in gpb-1(yz71) mutants under optimal and aversive conditions.(A) Dauer formation induced by aversive growth conditions caused ADF tph-1::gfp upregulation in WT and yz71mutants, as compared to their respective L4 stage siblings. (B) Mutation in cilia structural gene che-2 was capable of triggering ADF tph-1::gfp upregulation in yz71 mutants. (C) Pathogen PA14 failed to induce ADF tph-1::gfp upregulation in yz71 mutants, as comparing tph-1::gfp between 1st day adults fed PA14 and non-pathogenic bacterial control OP50 for 6 hr. gpb-1(g) transgene restored the PA14 response in yz71 mutants. (D) Comparing ADF tph-1::gfp between gpb-1(yz71) and ocr-2 TRPV channel mutants. In both mutants, ADF tph-1::gfp was diminished under optimal growth conditions, but enhanced in tir-1(yz68gf) background as compared to the yz71 and ocr-2 single mutants. yz71 and ocr-2 did not produce an additive effect. For each assay, the value of ADF GFP fluorescence in WT animals under a stress paradigm and that of mutants is normalized to the value of WT animals under optimal conditions. Data represent the average of ≥ 3 trials ± SEM, * p < 0.05, *** p < 0.001, t-test for two group comparisons, and ANOVA for multi-group/condition comparisons.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4581872&req=5

pgen.1005540.g003: tph-1::gfp expression in gpb-1(yz71) mutants under optimal and aversive conditions.(A) Dauer formation induced by aversive growth conditions caused ADF tph-1::gfp upregulation in WT and yz71mutants, as compared to their respective L4 stage siblings. (B) Mutation in cilia structural gene che-2 was capable of triggering ADF tph-1::gfp upregulation in yz71 mutants. (C) Pathogen PA14 failed to induce ADF tph-1::gfp upregulation in yz71 mutants, as comparing tph-1::gfp between 1st day adults fed PA14 and non-pathogenic bacterial control OP50 for 6 hr. gpb-1(g) transgene restored the PA14 response in yz71 mutants. (D) Comparing ADF tph-1::gfp between gpb-1(yz71) and ocr-2 TRPV channel mutants. In both mutants, ADF tph-1::gfp was diminished under optimal growth conditions, but enhanced in tir-1(yz68gf) background as compared to the yz71 and ocr-2 single mutants. yz71 and ocr-2 did not produce an additive effect. For each assay, the value of ADF GFP fluorescence in WT animals under a stress paradigm and that of mutants is normalized to the value of WT animals under optimal conditions. Data represent the average of ≥ 3 trials ± SEM, * p < 0.05, *** p < 0.001, t-test for two group comparisons, and ANOVA for multi-group/condition comparisons.
Mentions: A stress-resistant state called dauer can be induced by a defined set of aversive growth conditions and is the most commonly used paradigm in C. elegans stress response studies [24]. Dauers enhance a battery of stress responsive genes to produce a series of physiological, morphological and behavioral remodeling [24]. Previously, we identified that alteration of ADF sensory cilia architecture caused either by dauer formation or genetic mutations in intraflagellar transport (IFT) triggers ADF tph-1 upregulation [10]. When yz71 mutants were induced to form dauers, ADF tph-1::gfp was significantly enhanced compared to their siblings under optimal growth conditions (Fig 3A). Likewise, we observed elevated ADF tph-1::gfp in yz71 mutants carrying defective IFT component che-2 (Fig 3B). However, ADF tph-1::gfp levels in yz71 dauers and yz71;che-2 double mutants were lower than WT dauers and che-2 single mutants, respectively (Fig 3A and 3B). These observations support the idea that dauer formation and GPB-1 regulate two mechanistically separable layers of tph-1 expression. yz71 mutants do not impair tph-1 upregulation induced by dauer formation or cilia structural alterations but have a lower baseline of tph-1 expression.

Bottom Line: We found that signaling through cell autonomous GPB-1 to the OCR-2 TRPV channel defines the baseline expression of 5-HT synthesis enzyme tryptophan hydroxylase tph-1 in ADF chemosensory neurons.These results revealed a Gβ-mediated signaling operating in differentiated cells to specify intrinsic functional properties, and indicate that baseline TPH expression is not a default generic serotonergic fate, but is programmed in a cell-specific manner in the mature nervous system.Cell-specific regulation of TPH expression could be a general principle for tailored steady state 5-HT synthesis in functionally distinct neurons and their regulation of innate behavior.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States of America.

ABSTRACT
Heterotrimeric G proteins regulate a vast array of cellular functions via specific intracellular effectors. Accumulating pharmacological and biochemical studies implicate Gβ subunits as signaling molecules interacting directly with a wide range of effectors to modulate downstream cellular responses, in addition to their role in regulating Gα subunit activities. However, the native biological roles of Gβ-mediated signaling pathways in vivo have been characterized only in a few cases. Here, we identified a Gβ GPB-1 signaling pathway operating in specific serotonergic neurons to the define steady state serotonin (5-HT) synthesis, through a genetic screen for 5-HT synthesis mutants in Caenorhabditis elegans. We found that signaling through cell autonomous GPB-1 to the OCR-2 TRPV channel defines the baseline expression of 5-HT synthesis enzyme tryptophan hydroxylase tph-1 in ADF chemosensory neurons. This Gβ signaling pathway is not essential for establishing the serotonergic cell fates and is mechanistically separated from stress-induced tph-1 upregulation. We identified that ADF-produced 5-HT controls specific innate rhythmic behaviors. These results revealed a Gβ-mediated signaling operating in differentiated cells to specify intrinsic functional properties, and indicate that baseline TPH expression is not a default generic serotonergic fate, but is programmed in a cell-specific manner in the mature nervous system. Cell-specific regulation of TPH expression could be a general principle for tailored steady state 5-HT synthesis in functionally distinct neurons and their regulation of innate behavior.

No MeSH data available.


Related in: MedlinePlus