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The molecular basis for water taste in Drosophila.

Cameron P, Hiroi M, Ngai J, Scott K - Nature (2010)

Bottom Line: Here we identify a member of the degenerin/epithelial sodium channel family, PPK28, as an osmosensitive ion channel that mediates the cellular and behavioural response to water.We use molecular, cellular, calcium imaging and electrophysiological approaches to show that ppk28 is expressed in water-sensing neurons, and that loss of ppk28 abolishes water sensitivity.These studies link an osmosensitive ion channel to water taste detection and drinking behaviour, providing the framework for examining the molecular basis for water detection in other animals.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, CA, USA.

ABSTRACT
The detection of water and the regulation of water intake are essential for animals to maintain proper osmotic homeostasis. Drosophila and other insects have gustatory sensory neurons that mediate the recognition of external water sources, but little is known about the underlying molecular mechanism for water taste detection. Here we identify a member of the degenerin/epithelial sodium channel family, PPK28, as an osmosensitive ion channel that mediates the cellular and behavioural response to water. We use molecular, cellular, calcium imaging and electrophysiological approaches to show that ppk28 is expressed in water-sensing neurons, and that loss of ppk28 abolishes water sensitivity. Moreover, ectopic expression of ppk28 confers water sensitivity to bitter-sensing gustatory neurons in the fly and sensitivity to hypo-osmotic solutions when expressed in heterologous cells. These studies link an osmosensitive ion channel to water taste detection and drinking behaviour, providing the framework for examining the molecular basis for water detection in other animals.

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ppk28-Gal4 labels neurons that respond to water. a, b. ppk28-Gal4 drives GFP in (a) gustatory neurons and (b) their axons in the subesophageal ganglion. ppk28 was previously reported in larval tracheae27. c, d. ppk28 neurons (magenta) do not contain markers for (c) sugar neurons (Gr5a, green) or (d) bitter neurons (Gr66a, green). Scale bar in a-d is 50 μm e. ppk28-Gal4 neurons respond to water. G-CaMP fluorescent changes to water, NaCl, sucrose, ribose, n-methyl-d-glucamine (NMDG) and polyethylene glycol (PEG). Responses different than water by t-test are 0.2M NaCl (P=0.046), 0.5M NaCl (P=0.004), 1M NaCl (P=0.0003), 0.5M sucrose (P=3.27E-5), 1M sucrose (P=1.11E-5), 0.5M ribose (P=0.0008), 1M ribose (P=0.0003), 1M NMDG (P=0.0014), 20% PEG (P=0.028). n=4-11 flies/compound ± s.e.m.
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Figure 1: ppk28-Gal4 labels neurons that respond to water. a, b. ppk28-Gal4 drives GFP in (a) gustatory neurons and (b) their axons in the subesophageal ganglion. ppk28 was previously reported in larval tracheae27. c, d. ppk28 neurons (magenta) do not contain markers for (c) sugar neurons (Gr5a, green) or (d) bitter neurons (Gr66a, green). Scale bar in a-d is 50 μm e. ppk28-Gal4 neurons respond to water. G-CaMP fluorescent changes to water, NaCl, sucrose, ribose, n-methyl-d-glucamine (NMDG) and polyethylene glycol (PEG). Responses different than water by t-test are 0.2M NaCl (P=0.046), 0.5M NaCl (P=0.004), 1M NaCl (P=0.0003), 0.5M sucrose (P=3.27E-5), 1M sucrose (P=1.11E-5), 0.5M ribose (P=0.0008), 1M ribose (P=0.0003), 1M NMDG (P=0.0014), 20% PEG (P=0.028). n=4-11 flies/compound ± s.e.m.

Mentions: In the mammalian gustatory system, ion channels mediate the detection of sour and salt tastes8, suggesting that ion channel genes may also participate in Drosophila taste detection. We therefore examined the expression pattern of candidate taste-enriched ion channels. The putative promoter of one gene, pickpocket 28 (ppk28), directed robust reporter expression in taste neurons on the proboscis (Fig. 1a). ppk28 belongs to the Degenerin/Epithelial sodium channel family (Deg/ENaC) and these channels are involved in the detection of diverse stimuli, including mechanosensory stimuli, acids and sodium ions5. In the brain, ppk28-Gal4 drives expression of GFP in gustatory sensory axons that project to the primary taste region, the subesophageal ganglion (Fig. 1b; Supplementary Fig. 2). In situ hybridization experiments confirmed that transgenic expression recapitulates that of the endogenous gene, as 48/52 of ppk28-Gal4 neurons expressed endogenous ppk28.


The molecular basis for water taste in Drosophila.

Cameron P, Hiroi M, Ngai J, Scott K - Nature (2010)

ppk28-Gal4 labels neurons that respond to water. a, b. ppk28-Gal4 drives GFP in (a) gustatory neurons and (b) their axons in the subesophageal ganglion. ppk28 was previously reported in larval tracheae27. c, d. ppk28 neurons (magenta) do not contain markers for (c) sugar neurons (Gr5a, green) or (d) bitter neurons (Gr66a, green). Scale bar in a-d is 50 μm e. ppk28-Gal4 neurons respond to water. G-CaMP fluorescent changes to water, NaCl, sucrose, ribose, n-methyl-d-glucamine (NMDG) and polyethylene glycol (PEG). Responses different than water by t-test are 0.2M NaCl (P=0.046), 0.5M NaCl (P=0.004), 1M NaCl (P=0.0003), 0.5M sucrose (P=3.27E-5), 1M sucrose (P=1.11E-5), 0.5M ribose (P=0.0008), 1M ribose (P=0.0003), 1M NMDG (P=0.0014), 20% PEG (P=0.028). n=4-11 flies/compound ± s.e.m.
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getmorefigures.php?uid=PMC2865571&req=5

Figure 1: ppk28-Gal4 labels neurons that respond to water. a, b. ppk28-Gal4 drives GFP in (a) gustatory neurons and (b) their axons in the subesophageal ganglion. ppk28 was previously reported in larval tracheae27. c, d. ppk28 neurons (magenta) do not contain markers for (c) sugar neurons (Gr5a, green) or (d) bitter neurons (Gr66a, green). Scale bar in a-d is 50 μm e. ppk28-Gal4 neurons respond to water. G-CaMP fluorescent changes to water, NaCl, sucrose, ribose, n-methyl-d-glucamine (NMDG) and polyethylene glycol (PEG). Responses different than water by t-test are 0.2M NaCl (P=0.046), 0.5M NaCl (P=0.004), 1M NaCl (P=0.0003), 0.5M sucrose (P=3.27E-5), 1M sucrose (P=1.11E-5), 0.5M ribose (P=0.0008), 1M ribose (P=0.0003), 1M NMDG (P=0.0014), 20% PEG (P=0.028). n=4-11 flies/compound ± s.e.m.
Mentions: In the mammalian gustatory system, ion channels mediate the detection of sour and salt tastes8, suggesting that ion channel genes may also participate in Drosophila taste detection. We therefore examined the expression pattern of candidate taste-enriched ion channels. The putative promoter of one gene, pickpocket 28 (ppk28), directed robust reporter expression in taste neurons on the proboscis (Fig. 1a). ppk28 belongs to the Degenerin/Epithelial sodium channel family (Deg/ENaC) and these channels are involved in the detection of diverse stimuli, including mechanosensory stimuli, acids and sodium ions5. In the brain, ppk28-Gal4 drives expression of GFP in gustatory sensory axons that project to the primary taste region, the subesophageal ganglion (Fig. 1b; Supplementary Fig. 2). In situ hybridization experiments confirmed that transgenic expression recapitulates that of the endogenous gene, as 48/52 of ppk28-Gal4 neurons expressed endogenous ppk28.

Bottom Line: Here we identify a member of the degenerin/epithelial sodium channel family, PPK28, as an osmosensitive ion channel that mediates the cellular and behavioural response to water.We use molecular, cellular, calcium imaging and electrophysiological approaches to show that ppk28 is expressed in water-sensing neurons, and that loss of ppk28 abolishes water sensitivity.These studies link an osmosensitive ion channel to water taste detection and drinking behaviour, providing the framework for examining the molecular basis for water detection in other animals.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, CA, USA.

ABSTRACT
The detection of water and the regulation of water intake are essential for animals to maintain proper osmotic homeostasis. Drosophila and other insects have gustatory sensory neurons that mediate the recognition of external water sources, but little is known about the underlying molecular mechanism for water taste detection. Here we identify a member of the degenerin/epithelial sodium channel family, PPK28, as an osmosensitive ion channel that mediates the cellular and behavioural response to water. We use molecular, cellular, calcium imaging and electrophysiological approaches to show that ppk28 is expressed in water-sensing neurons, and that loss of ppk28 abolishes water sensitivity. Moreover, ectopic expression of ppk28 confers water sensitivity to bitter-sensing gustatory neurons in the fly and sensitivity to hypo-osmotic solutions when expressed in heterologous cells. These studies link an osmosensitive ion channel to water taste detection and drinking behaviour, providing the framework for examining the molecular basis for water detection in other animals.

Show MeSH
Related in: MedlinePlus