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Feeding state, insulin and NPR-1 modulate chemoreceptor gene expression via integration of sensory and circuit inputs.

Gruner M, Nelson D, Winbush A, Hintz R, Ryu L, Chung SH, Kim K, Gabel CV, van der Linden AM - PLoS Genet. (2014)

Bottom Line: Using physical and genetic manipulation of ADL neurons, we show that sensory inputs from food presence and ADL neural output regulate srh-234 expression.While KIN-29 and DAF-2 act primarily via the MEF-2 (MEF2) and DAF-16 (FOXO) transcription factors to regulate srh-234 expression in ADL neurons, OCR-2 and NPR-1 likely act via a calcium-dependent but MEF-2- and DAF-16-independent pathway.Together, our results suggest that sensory- and circuit-mediated regulation of chemoreceptor genes via multiple pathways may allow animals to precisely regulate and fine-tune their chemosensory responses as a function of internal and external conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Nevada, Reno, Nevada, United States of America.

ABSTRACT
Feeding state and food availability can dramatically alter an animals' sensory response to chemicals in its environment. Dynamic changes in the expression of chemoreceptor genes may underlie some of these food and state-dependent changes in chemosensory behavior, but the mechanisms underlying these expression changes are unknown. Here, we identified a KIN-29 (SIK)-dependent chemoreceptor, srh-234, in C. elegans whose expression in the ADL sensory neuron type is regulated by integration of sensory and internal feeding state signals. We show that in addition to KIN-29, signaling is mediated by the DAF-2 insulin-like receptor, OCR-2 TRPV channel, and NPR-1 neuropeptide receptor. Cell-specific rescue experiments suggest that DAF-2 and OCR-2 act in ADL, while NPR-1 acts in the RMG interneurons. NPR-1-mediated regulation of srh-234 is dependent on gap-junctions, implying that circuit inputs regulate the expression of chemoreceptor genes in sensory neurons. Using physical and genetic manipulation of ADL neurons, we show that sensory inputs from food presence and ADL neural output regulate srh-234 expression. While KIN-29 and DAF-2 act primarily via the MEF-2 (MEF2) and DAF-16 (FOXO) transcription factors to regulate srh-234 expression in ADL neurons, OCR-2 and NPR-1 likely act via a calcium-dependent but MEF-2- and DAF-16-independent pathway. Together, our results suggest that sensory- and circuit-mediated regulation of chemoreceptor genes via multiple pathways may allow animals to precisely regulate and fine-tune their chemosensory responses as a function of internal and external conditions.

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External food presence and internal state signals alter srh-234 expression levels.A) Percentage of animals expressing srh-234p::gfp at wild-type levels when fed with E. coli OP50 food (OP50), aztreonam-treated E. coli OP50 food (inedible OP50), or no food (no OP50) for 24 and 48 hours. Young adult animals grown on edible E. coli OP50 food were divided into two groups: a fed group maintained in the presence of food, and a starved group maintained in the absence of food for 6–12 hours. We confirmed that srh-234 expression levels upon starvation were reduced. Subsequently, adults were picked onto new NGM plates seeded with either edible E. coli OP50, no E. coli OP50, or inedible E. coli OP50 food (see Material and Methods). B) Percentage of eat-2(lf) mutants defective in food intake expressing srh-234p::gfp at wild-type levels. In all experiments, wild-type expression of srh-234p::gfp was defined as expression levels that allowed visualization of both the cell bodies and processes of at least one ADL neuron (see Material and Methods). Animals (n>150) were examined at 150× magnification for each condition or genotype. * indicates values that is different from that of wild-type animals at P<0.001, and n.s. indicates the values that are not significantly different between the different food conditions compared by brackets using a χ2 test of independence. Error bars denote the SEP.
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pgen-1004707-g002: External food presence and internal state signals alter srh-234 expression levels.A) Percentage of animals expressing srh-234p::gfp at wild-type levels when fed with E. coli OP50 food (OP50), aztreonam-treated E. coli OP50 food (inedible OP50), or no food (no OP50) for 24 and 48 hours. Young adult animals grown on edible E. coli OP50 food were divided into two groups: a fed group maintained in the presence of food, and a starved group maintained in the absence of food for 6–12 hours. We confirmed that srh-234 expression levels upon starvation were reduced. Subsequently, adults were picked onto new NGM plates seeded with either edible E. coli OP50, no E. coli OP50, or inedible E. coli OP50 food (see Material and Methods). B) Percentage of eat-2(lf) mutants defective in food intake expressing srh-234p::gfp at wild-type levels. In all experiments, wild-type expression of srh-234p::gfp was defined as expression levels that allowed visualization of both the cell bodies and processes of at least one ADL neuron (see Material and Methods). Animals (n>150) were examined at 150× magnification for each condition or genotype. * indicates values that is different from that of wild-type animals at P<0.001, and n.s. indicates the values that are not significantly different between the different food conditions compared by brackets using a χ2 test of independence. Error bars denote the SEP.

Mentions: The reduced srh-234 expression levels we observed in starved wild-type animals could arise as a consequence of an internal state of starvation triggered by a decrease in the ingestion of food, or alternatively, by an external sensory response as a result of a decrease in the perception of food. To distinguish between these possibilities, we exposed fed and starved wild-type adult animals carrying the srh-234p::gfp reporter to E. coli food treated with the antibiotic aztreonam, which results in bacteria that grow in long chains that C. elegans cannot eat due its large size, but still can smell and touch comparable to regular non-treated bacteria [24]. We found that fed animals placed on aztreonam-treated E. coli OP50 (inedible food) for 24 and 48 hours significantly reduces srh-234 expression mimicking the effects of starvation when compared to fed animals placed on non-treated E. coli OP50 (edible food) (Figure 2A). Consistent with these findings, loss-of-function (lf) mutations in eat-2 that result in animals with a pharyngeal pumping defect compromising their food ingestion, also reduce srh-234 expression on edible food (Figure 2B). Thus, the reduced srh-234 expression is likely due to an internal state response triggered by a decreased food ingestion. However, when we placed starved adult animals (in the absence of food for 6–12 hours) on aztreonam-treated E. coli OP50 (inedible food), we found that the srh-234 expression phenotype was not significantly different from their non-treated E. coli OP50 (edible food) counterpart as if they sense food presence correctly even when they cannot eat this food (Figure 2A). It is possible that starved animals in our experiments can ingest some of the inedible food but at a reduced amount. However, we found that animals placed on aztreonam-treated E. coli food have a starved appearance similar to starved animals placed on plates without any food. Moreover, we verified that aztreonam-treated E. coli cannot be eaten properly as we find that L1 larvae exposed to treated food used in our experiments do not sustain growth (98% of L1 animals placed on aztreonam-treated bacteria for 24 hours were arrested, as compared to 0% of L1 larvae placed on edible food). Thus, the perception of inedible food can override the effects of starvation on reducing srh-234 expression levels. In summary, our results suggest that the starvation-induced downregulation of srh-234 expression is likely a consequence of both sensory inputs associated with a decreased food presence, and an internal state of starvation triggered by a decrease in food ingestion.


Feeding state, insulin and NPR-1 modulate chemoreceptor gene expression via integration of sensory and circuit inputs.

Gruner M, Nelson D, Winbush A, Hintz R, Ryu L, Chung SH, Kim K, Gabel CV, van der Linden AM - PLoS Genet. (2014)

External food presence and internal state signals alter srh-234 expression levels.A) Percentage of animals expressing srh-234p::gfp at wild-type levels when fed with E. coli OP50 food (OP50), aztreonam-treated E. coli OP50 food (inedible OP50), or no food (no OP50) for 24 and 48 hours. Young adult animals grown on edible E. coli OP50 food were divided into two groups: a fed group maintained in the presence of food, and a starved group maintained in the absence of food for 6–12 hours. We confirmed that srh-234 expression levels upon starvation were reduced. Subsequently, adults were picked onto new NGM plates seeded with either edible E. coli OP50, no E. coli OP50, or inedible E. coli OP50 food (see Material and Methods). B) Percentage of eat-2(lf) mutants defective in food intake expressing srh-234p::gfp at wild-type levels. In all experiments, wild-type expression of srh-234p::gfp was defined as expression levels that allowed visualization of both the cell bodies and processes of at least one ADL neuron (see Material and Methods). Animals (n>150) were examined at 150× magnification for each condition or genotype. * indicates values that is different from that of wild-type animals at P<0.001, and n.s. indicates the values that are not significantly different between the different food conditions compared by brackets using a χ2 test of independence. Error bars denote the SEP.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4214617&req=5

pgen-1004707-g002: External food presence and internal state signals alter srh-234 expression levels.A) Percentage of animals expressing srh-234p::gfp at wild-type levels when fed with E. coli OP50 food (OP50), aztreonam-treated E. coli OP50 food (inedible OP50), or no food (no OP50) for 24 and 48 hours. Young adult animals grown on edible E. coli OP50 food were divided into two groups: a fed group maintained in the presence of food, and a starved group maintained in the absence of food for 6–12 hours. We confirmed that srh-234 expression levels upon starvation were reduced. Subsequently, adults were picked onto new NGM plates seeded with either edible E. coli OP50, no E. coli OP50, or inedible E. coli OP50 food (see Material and Methods). B) Percentage of eat-2(lf) mutants defective in food intake expressing srh-234p::gfp at wild-type levels. In all experiments, wild-type expression of srh-234p::gfp was defined as expression levels that allowed visualization of both the cell bodies and processes of at least one ADL neuron (see Material and Methods). Animals (n>150) were examined at 150× magnification for each condition or genotype. * indicates values that is different from that of wild-type animals at P<0.001, and n.s. indicates the values that are not significantly different between the different food conditions compared by brackets using a χ2 test of independence. Error bars denote the SEP.
Mentions: The reduced srh-234 expression levels we observed in starved wild-type animals could arise as a consequence of an internal state of starvation triggered by a decrease in the ingestion of food, or alternatively, by an external sensory response as a result of a decrease in the perception of food. To distinguish between these possibilities, we exposed fed and starved wild-type adult animals carrying the srh-234p::gfp reporter to E. coli food treated with the antibiotic aztreonam, which results in bacteria that grow in long chains that C. elegans cannot eat due its large size, but still can smell and touch comparable to regular non-treated bacteria [24]. We found that fed animals placed on aztreonam-treated E. coli OP50 (inedible food) for 24 and 48 hours significantly reduces srh-234 expression mimicking the effects of starvation when compared to fed animals placed on non-treated E. coli OP50 (edible food) (Figure 2A). Consistent with these findings, loss-of-function (lf) mutations in eat-2 that result in animals with a pharyngeal pumping defect compromising their food ingestion, also reduce srh-234 expression on edible food (Figure 2B). Thus, the reduced srh-234 expression is likely due to an internal state response triggered by a decreased food ingestion. However, when we placed starved adult animals (in the absence of food for 6–12 hours) on aztreonam-treated E. coli OP50 (inedible food), we found that the srh-234 expression phenotype was not significantly different from their non-treated E. coli OP50 (edible food) counterpart as if they sense food presence correctly even when they cannot eat this food (Figure 2A). It is possible that starved animals in our experiments can ingest some of the inedible food but at a reduced amount. However, we found that animals placed on aztreonam-treated E. coli food have a starved appearance similar to starved animals placed on plates without any food. Moreover, we verified that aztreonam-treated E. coli cannot be eaten properly as we find that L1 larvae exposed to treated food used in our experiments do not sustain growth (98% of L1 animals placed on aztreonam-treated bacteria for 24 hours were arrested, as compared to 0% of L1 larvae placed on edible food). Thus, the perception of inedible food can override the effects of starvation on reducing srh-234 expression levels. In summary, our results suggest that the starvation-induced downregulation of srh-234 expression is likely a consequence of both sensory inputs associated with a decreased food presence, and an internal state of starvation triggered by a decrease in food ingestion.

Bottom Line: Using physical and genetic manipulation of ADL neurons, we show that sensory inputs from food presence and ADL neural output regulate srh-234 expression.While KIN-29 and DAF-2 act primarily via the MEF-2 (MEF2) and DAF-16 (FOXO) transcription factors to regulate srh-234 expression in ADL neurons, OCR-2 and NPR-1 likely act via a calcium-dependent but MEF-2- and DAF-16-independent pathway.Together, our results suggest that sensory- and circuit-mediated regulation of chemoreceptor genes via multiple pathways may allow animals to precisely regulate and fine-tune their chemosensory responses as a function of internal and external conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Nevada, Reno, Nevada, United States of America.

ABSTRACT
Feeding state and food availability can dramatically alter an animals' sensory response to chemicals in its environment. Dynamic changes in the expression of chemoreceptor genes may underlie some of these food and state-dependent changes in chemosensory behavior, but the mechanisms underlying these expression changes are unknown. Here, we identified a KIN-29 (SIK)-dependent chemoreceptor, srh-234, in C. elegans whose expression in the ADL sensory neuron type is regulated by integration of sensory and internal feeding state signals. We show that in addition to KIN-29, signaling is mediated by the DAF-2 insulin-like receptor, OCR-2 TRPV channel, and NPR-1 neuropeptide receptor. Cell-specific rescue experiments suggest that DAF-2 and OCR-2 act in ADL, while NPR-1 acts in the RMG interneurons. NPR-1-mediated regulation of srh-234 is dependent on gap-junctions, implying that circuit inputs regulate the expression of chemoreceptor genes in sensory neurons. Using physical and genetic manipulation of ADL neurons, we show that sensory inputs from food presence and ADL neural output regulate srh-234 expression. While KIN-29 and DAF-2 act primarily via the MEF-2 (MEF2) and DAF-16 (FOXO) transcription factors to regulate srh-234 expression in ADL neurons, OCR-2 and NPR-1 likely act via a calcium-dependent but MEF-2- and DAF-16-independent pathway. Together, our results suggest that sensory- and circuit-mediated regulation of chemoreceptor genes via multiple pathways may allow animals to precisely regulate and fine-tune their chemosensory responses as a function of internal and external conditions.

Show MeSH
Related in: MedlinePlus