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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

G162E occurs at the Gβ surface that binds to Gα switch II helix and Gβ effectors.(A) Comparing amino acid sequence surrounding G162 (red boxed) between C. elegans GPB-1, bovine (B.t.) Gβ1, and human (H.s.) Gβ1 and Gβ2, all of which contain 340 amino acid residues and the numbers refer to residue positions in the corresponding proteins. (B) Modeling G162E substitution over bovine β1. (Bi) Cartoon presentation of the crystallographic structure of rat Giα1 and bovine β1γ2 heterotrimer rendered with PyMOL software. β subunit is colored cyan, and γ subunit colored orange. G162 (the side chain colored red) is located on the surface of the narrow side of the propeller architecture of Gβ. (Bii) Another view of the heterotrimer showing the interactions between Gβ and GDP-bound Gα (green). G162 is located on the surface that binds to the Gα switch II helix (yellow). GDP is in white, and the nearby Gα-S47 that is critical for the GTP binding is colored magenta. (Biii) An enlarged view showing the interface between Gβ and Gα switch II helix. Gβ-G162 sits nearby Gβ-Y145, a critical residue in an effector binding hotspot [17]. Gβ-G162 is in close proximity to Gα-S206 in the switch II helix. The conformation of Gα-G202 and G203 is critical for GTP binding [32]. (Biv) An enlarged view showing the Gβ and Gα switch II interface, with G162 changed to E in the Gβ sequence. (C) GPB-1 immunostaining. Ci and Ciii. In both WT and yz71 two-cell embryos, GPB-1 was enriched in the asters (arrowheads) and in the region between cells. Cii and Civ. In WT and yz71 animals, GPB-1 can be detected in the cell membrane in neurons. Cv. gpb-1(g) overexpression transgenic animals showing GPB-1 localized to axons and dendrites.
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pgen.1005540.g005: G162E occurs at the Gβ surface that binds to Gα switch II helix and Gβ effectors.(A) Comparing amino acid sequence surrounding G162 (red boxed) between C. elegans GPB-1, bovine (B.t.) Gβ1, and human (H.s.) Gβ1 and Gβ2, all of which contain 340 amino acid residues and the numbers refer to residue positions in the corresponding proteins. (B) Modeling G162E substitution over bovine β1. (Bi) Cartoon presentation of the crystallographic structure of rat Giα1 and bovine β1γ2 heterotrimer rendered with PyMOL software. β subunit is colored cyan, and γ subunit colored orange. G162 (the side chain colored red) is located on the surface of the narrow side of the propeller architecture of Gβ. (Bii) Another view of the heterotrimer showing the interactions between Gβ and GDP-bound Gα (green). G162 is located on the surface that binds to the Gα switch II helix (yellow). GDP is in white, and the nearby Gα-S47 that is critical for the GTP binding is colored magenta. (Biii) An enlarged view showing the interface between Gβ and Gα switch II helix. Gβ-G162 sits nearby Gβ-Y145, a critical residue in an effector binding hotspot [17]. Gβ-G162 is in close proximity to Gα-S206 in the switch II helix. The conformation of Gα-G202 and G203 is critical for GTP binding [32]. (Biv) An enlarged view showing the Gβ and Gα switch II interface, with G162 changed to E in the Gβ sequence. (C) GPB-1 immunostaining. Ci and Ciii. In both WT and yz71 two-cell embryos, GPB-1 was enriched in the asters (arrowheads) and in the region between cells. Cii and Civ. In WT and yz71 animals, GPB-1 can be detected in the cell membrane in neurons. Cv. gpb-1(g) overexpression transgenic animals showing GPB-1 localized to axons and dendrites.

Mentions: How might GPB-1(G162E) disrupt G protein functionalities? GPB-1 shares 86% amino acid identity with human and bovine Gβ1 (Fig 5A). To gain insights into GPB-1 functional mechanisms regulating tph-1 expression, we modeled GPB-1(G162E) over the crystallographic structure of rat Giα1 and bovine β1γ2 heterotrimer [28]. The seven WD40 repeats of Gβ fold into a circular β-bladed propeller which makes two major contacts with Gα: the side of the propeller interacts with the Gα N-terminal helix, and the narrow propeller region forms an interface with the Gα switch II helix [28] (Fig 5Bi and 5Bii). Formation of Gβ/Gα switch II interface favors the inactive GDP-binding state, whereas GTP binding of Gα triggers the switch II helix rotating 120° thereby permitting both Gβ and Gα proteins to interact with their effectors [28,29]. G162E occurs right at the Gβ/Gα switch II interface (Fig 5Biii and 5Biv).


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)

G162E occurs at the Gβ surface that binds to Gα switch II helix and Gβ effectors.(A) Comparing amino acid sequence surrounding G162 (red boxed) between C. elegans GPB-1, bovine (B.t.) Gβ1, and human (H.s.) Gβ1 and Gβ2, all of which contain 340 amino acid residues and the numbers refer to residue positions in the corresponding proteins. (B) Modeling G162E substitution over bovine β1. (Bi) Cartoon presentation of the crystallographic structure of rat Giα1 and bovine β1γ2 heterotrimer rendered with PyMOL software. β subunit is colored cyan, and γ subunit colored orange. G162 (the side chain colored red) is located on the surface of the narrow side of the propeller architecture of Gβ. (Bii) Another view of the heterotrimer showing the interactions between Gβ and GDP-bound Gα (green). G162 is located on the surface that binds to the Gα switch II helix (yellow). GDP is in white, and the nearby Gα-S47 that is critical for the GTP binding is colored magenta. (Biii) An enlarged view showing the interface between Gβ and Gα switch II helix. Gβ-G162 sits nearby Gβ-Y145, a critical residue in an effector binding hotspot [17]. Gβ-G162 is in close proximity to Gα-S206 in the switch II helix. The conformation of Gα-G202 and G203 is critical for GTP binding [32]. (Biv) An enlarged view showing the Gβ and Gα switch II interface, with G162 changed to E in the Gβ sequence. (C) GPB-1 immunostaining. Ci and Ciii. In both WT and yz71 two-cell embryos, GPB-1 was enriched in the asters (arrowheads) and in the region between cells. Cii and Civ. In WT and yz71 animals, GPB-1 can be detected in the cell membrane in neurons. Cv. gpb-1(g) overexpression transgenic animals showing GPB-1 localized to axons and dendrites.
© Copyright Policy
Related In: Results  -  Collection

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

pgen.1005540.g005: G162E occurs at the Gβ surface that binds to Gα switch II helix and Gβ effectors.(A) Comparing amino acid sequence surrounding G162 (red boxed) between C. elegans GPB-1, bovine (B.t.) Gβ1, and human (H.s.) Gβ1 and Gβ2, all of which contain 340 amino acid residues and the numbers refer to residue positions in the corresponding proteins. (B) Modeling G162E substitution over bovine β1. (Bi) Cartoon presentation of the crystallographic structure of rat Giα1 and bovine β1γ2 heterotrimer rendered with PyMOL software. β subunit is colored cyan, and γ subunit colored orange. G162 (the side chain colored red) is located on the surface of the narrow side of the propeller architecture of Gβ. (Bii) Another view of the heterotrimer showing the interactions between Gβ and GDP-bound Gα (green). G162 is located on the surface that binds to the Gα switch II helix (yellow). GDP is in white, and the nearby Gα-S47 that is critical for the GTP binding is colored magenta. (Biii) An enlarged view showing the interface between Gβ and Gα switch II helix. Gβ-G162 sits nearby Gβ-Y145, a critical residue in an effector binding hotspot [17]. Gβ-G162 is in close proximity to Gα-S206 in the switch II helix. The conformation of Gα-G202 and G203 is critical for GTP binding [32]. (Biv) An enlarged view showing the Gβ and Gα switch II interface, with G162 changed to E in the Gβ sequence. (C) GPB-1 immunostaining. Ci and Ciii. In both WT and yz71 two-cell embryos, GPB-1 was enriched in the asters (arrowheads) and in the region between cells. Cii and Civ. In WT and yz71 animals, GPB-1 can be detected in the cell membrane in neurons. Cv. gpb-1(g) overexpression transgenic animals showing GPB-1 localized to axons and dendrites.
Mentions: How might GPB-1(G162E) disrupt G protein functionalities? GPB-1 shares 86% amino acid identity with human and bovine Gβ1 (Fig 5A). To gain insights into GPB-1 functional mechanisms regulating tph-1 expression, we modeled GPB-1(G162E) over the crystallographic structure of rat Giα1 and bovine β1γ2 heterotrimer [28]. The seven WD40 repeats of Gβ fold into a circular β-bladed propeller which makes two major contacts with Gα: the side of the propeller interacts with the Gα N-terminal helix, and the narrow propeller region forms an interface with the Gα switch II helix [28] (Fig 5Bi and 5Bii). Formation of Gβ/Gα switch II interface favors the inactive GDP-binding state, whereas GTP binding of Gα triggers the switch II helix rotating 120° thereby permitting both Gβ and Gα proteins to interact with their effectors [28,29]. G162E occurs right at the Gβ/Gα switch II interface (Fig 5Biii and 5Biv).

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