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Rewiring neural circuits by the insertion of ectopic electrical synapses in transgenic C. elegans.

Rabinowitch I, Chatzigeorgiou M, Zhao B, Treinin M, Schafer WR - Nat Commun (2014)

Bottom Line: We added electrical synapses composed of the vertebrate gap junction protein Cx36 between Caenorhabditis elegans chemosensory neurons with opposite intrinsic responses to salt.In a second example, introducing Cx36 into an inhibitory chemical synapse between an olfactory receptor neuron and an interneuron changed the sign of the connection from negative to positive, and abolished the animal's behavioural response to benzaldehyde.These data demonstrate a synthetic strategy to rewire behavioural circuits by engineering synaptic connectivity in C. elegans.

View Article: PubMed Central - PubMed

Affiliation: 1] Division of Cell Biology, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK [2] Department of Medical Neurobiology, Hadassah Medical School, Hebrew University of Jerusalem, Jerusalem 9112102, Israel [3].

ABSTRACT
Neural circuits are functional ensembles of neurons that are selectively interconnected by chemical or electrical synapses. Here we describe a synthetic biology approach to the study of neural circuits, whereby new electrical synapses can be introduced in novel sites in the neuronal circuitry to reprogram behaviour. We added electrical synapses composed of the vertebrate gap junction protein Cx36 between Caenorhabditis elegans chemosensory neurons with opposite intrinsic responses to salt. Connecting these neurons by an ectopic electrical synapse led to a loss of lateral asymmetry and altered chemotaxis behaviour. In a second example, introducing Cx36 into an inhibitory chemical synapse between an olfactory receptor neuron and an interneuron changed the sign of the connection from negative to positive, and abolished the animal's behavioural response to benzaldehyde. These data demonstrate a synthetic strategy to rewire behavioural circuits by engineering synaptic connectivity in C. elegans.

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An engineered electrical synaptic connection functionally couples ASER and ASEL.(a) ASEL and ASER participate in a circuit for salt sensation and do not have any natural electrical connections. Chemical synapses between ASEL and ASER may be present in wild-type animals22, although the loss of synaptic transmission is not reported to affect ASEL and ASER sensory responses18. (b) The axons of ASER (red) and ASEL (green) appear to contact each other, as revealed by confocal microscopy. Shown is a three-dimensional confocal image of strain AQ3309 (gcy-7::gfp, gcy-5::mCherry; see strain list). (c) Confocal image of strain AQ3311, in which ASEL (green) expresses the genetically encoded calcium indicator YC3.60 and Cx36 tagged with mCherry (red). Cx36 puncta in the cell body (yellow arrow), dendrite (blue arrows) and axon (white arrows) are indicated. Scale bar, 20 μm. (d,e) Calcium imaging of ASER and ASEL responses to a downstep (d) or upstep (e) in NaCl concentration in wild-type worms and in worms expressing Cx36 in both ASER and ASEL. (f–i) Calcium imaging of ASER (f,h) or ASEL (g,i) responses to a downstep (f,g) or upstep (h,i) in NaCl concentration in wild-type worms and in worms expressing Cx36 in ASER (f,h) or ASEL (g,i) alone. At the top of each panel are averaged traces with shaded regions indicating s.e.m.; blue traces indicate wild-type, purple traces single neuron connexin lines, and red traces lines expressing Cx36 in both ASEL and ASER. At the bottom of each panel are percent mean fluorescent ratios, 10 s after compared with 10 s before stimulus onset. Two-tailed unpaired t-tests, **P<0.01, ***P<0.001, NS, not significant. Error bars represent s.e.m. Numbers on bars indicate sample sizes.
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f1: An engineered electrical synaptic connection functionally couples ASER and ASEL.(a) ASEL and ASER participate in a circuit for salt sensation and do not have any natural electrical connections. Chemical synapses between ASEL and ASER may be present in wild-type animals22, although the loss of synaptic transmission is not reported to affect ASEL and ASER sensory responses18. (b) The axons of ASER (red) and ASEL (green) appear to contact each other, as revealed by confocal microscopy. Shown is a three-dimensional confocal image of strain AQ3309 (gcy-7::gfp, gcy-5::mCherry; see strain list). (c) Confocal image of strain AQ3311, in which ASEL (green) expresses the genetically encoded calcium indicator YC3.60 and Cx36 tagged with mCherry (red). Cx36 puncta in the cell body (yellow arrow), dendrite (blue arrows) and axon (white arrows) are indicated. Scale bar, 20 μm. (d,e) Calcium imaging of ASER and ASEL responses to a downstep (d) or upstep (e) in NaCl concentration in wild-type worms and in worms expressing Cx36 in both ASER and ASEL. (f–i) Calcium imaging of ASER (f,h) or ASEL (g,i) responses to a downstep (f,g) or upstep (h,i) in NaCl concentration in wild-type worms and in worms expressing Cx36 in ASER (f,h) or ASEL (g,i) alone. At the top of each panel are averaged traces with shaded regions indicating s.e.m.; blue traces indicate wild-type, purple traces single neuron connexin lines, and red traces lines expressing Cx36 in both ASEL and ASER. At the bottom of each panel are percent mean fluorescent ratios, 10 s after compared with 10 s before stimulus onset. Two-tailed unpaired t-tests, **P<0.01, ***P<0.001, NS, not significant. Error bars represent s.e.m. Numbers on bars indicate sample sizes.

Mentions: We first investigated the possibility of rewiring neuronal connections in vivo using the neural circuit involved in salt chemotaxis. C. elegans navigates up gradients of sodium chloride and other salts in part through a biased random walk16, combining forward travel with stochastically occurring reorienting turnings and reversals. The primary neurons sensing attractive concentrations of salt are the bilaterally symmetric ASE neurons17; ASEL is an ON cell that is stimulated by an increase in salt concentration, while ASER is an OFF cell stimulated by a salt concentration decrease18. Unlike most bilateral sensory neuron pairs in C. elegans, the ASEL and ASER neurons are not normally connected by gap junctions (Fig. 1a). Published connectome data likewise report no chemical synapses between ASEL and ASER1920, although more recent online data based on computer-aided reconstructions2122 suggest some may exist. Moreover, confocal imaging of ASER and ASEL, labelled with expressed fluorescent proteins of different colours, showed that the processes of these two neurons are physically adjacent within the nerve ring (Fig. 1b).


Rewiring neural circuits by the insertion of ectopic electrical synapses in transgenic C. elegans.

Rabinowitch I, Chatzigeorgiou M, Zhao B, Treinin M, Schafer WR - Nat Commun (2014)

An engineered electrical synaptic connection functionally couples ASER and ASEL.(a) ASEL and ASER participate in a circuit for salt sensation and do not have any natural electrical connections. Chemical synapses between ASEL and ASER may be present in wild-type animals22, although the loss of synaptic transmission is not reported to affect ASEL and ASER sensory responses18. (b) The axons of ASER (red) and ASEL (green) appear to contact each other, as revealed by confocal microscopy. Shown is a three-dimensional confocal image of strain AQ3309 (gcy-7::gfp, gcy-5::mCherry; see strain list). (c) Confocal image of strain AQ3311, in which ASEL (green) expresses the genetically encoded calcium indicator YC3.60 and Cx36 tagged with mCherry (red). Cx36 puncta in the cell body (yellow arrow), dendrite (blue arrows) and axon (white arrows) are indicated. Scale bar, 20 μm. (d,e) Calcium imaging of ASER and ASEL responses to a downstep (d) or upstep (e) in NaCl concentration in wild-type worms and in worms expressing Cx36 in both ASER and ASEL. (f–i) Calcium imaging of ASER (f,h) or ASEL (g,i) responses to a downstep (f,g) or upstep (h,i) in NaCl concentration in wild-type worms and in worms expressing Cx36 in ASER (f,h) or ASEL (g,i) alone. At the top of each panel are averaged traces with shaded regions indicating s.e.m.; blue traces indicate wild-type, purple traces single neuron connexin lines, and red traces lines expressing Cx36 in both ASEL and ASER. At the bottom of each panel are percent mean fluorescent ratios, 10 s after compared with 10 s before stimulus onset. Two-tailed unpaired t-tests, **P<0.01, ***P<0.001, NS, not significant. Error bars represent s.e.m. Numbers on bars indicate sample sizes.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4109004&req=5

f1: An engineered electrical synaptic connection functionally couples ASER and ASEL.(a) ASEL and ASER participate in a circuit for salt sensation and do not have any natural electrical connections. Chemical synapses between ASEL and ASER may be present in wild-type animals22, although the loss of synaptic transmission is not reported to affect ASEL and ASER sensory responses18. (b) The axons of ASER (red) and ASEL (green) appear to contact each other, as revealed by confocal microscopy. Shown is a three-dimensional confocal image of strain AQ3309 (gcy-7::gfp, gcy-5::mCherry; see strain list). (c) Confocal image of strain AQ3311, in which ASEL (green) expresses the genetically encoded calcium indicator YC3.60 and Cx36 tagged with mCherry (red). Cx36 puncta in the cell body (yellow arrow), dendrite (blue arrows) and axon (white arrows) are indicated. Scale bar, 20 μm. (d,e) Calcium imaging of ASER and ASEL responses to a downstep (d) or upstep (e) in NaCl concentration in wild-type worms and in worms expressing Cx36 in both ASER and ASEL. (f–i) Calcium imaging of ASER (f,h) or ASEL (g,i) responses to a downstep (f,g) or upstep (h,i) in NaCl concentration in wild-type worms and in worms expressing Cx36 in ASER (f,h) or ASEL (g,i) alone. At the top of each panel are averaged traces with shaded regions indicating s.e.m.; blue traces indicate wild-type, purple traces single neuron connexin lines, and red traces lines expressing Cx36 in both ASEL and ASER. At the bottom of each panel are percent mean fluorescent ratios, 10 s after compared with 10 s before stimulus onset. Two-tailed unpaired t-tests, **P<0.01, ***P<0.001, NS, not significant. Error bars represent s.e.m. Numbers on bars indicate sample sizes.
Mentions: We first investigated the possibility of rewiring neuronal connections in vivo using the neural circuit involved in salt chemotaxis. C. elegans navigates up gradients of sodium chloride and other salts in part through a biased random walk16, combining forward travel with stochastically occurring reorienting turnings and reversals. The primary neurons sensing attractive concentrations of salt are the bilaterally symmetric ASE neurons17; ASEL is an ON cell that is stimulated by an increase in salt concentration, while ASER is an OFF cell stimulated by a salt concentration decrease18. Unlike most bilateral sensory neuron pairs in C. elegans, the ASEL and ASER neurons are not normally connected by gap junctions (Fig. 1a). Published connectome data likewise report no chemical synapses between ASEL and ASER1920, although more recent online data based on computer-aided reconstructions2122 suggest some may exist. Moreover, confocal imaging of ASER and ASEL, labelled with expressed fluorescent proteins of different colours, showed that the processes of these two neurons are physically adjacent within the nerve ring (Fig. 1b).

Bottom Line: We added electrical synapses composed of the vertebrate gap junction protein Cx36 between Caenorhabditis elegans chemosensory neurons with opposite intrinsic responses to salt.In a second example, introducing Cx36 into an inhibitory chemical synapse between an olfactory receptor neuron and an interneuron changed the sign of the connection from negative to positive, and abolished the animal's behavioural response to benzaldehyde.These data demonstrate a synthetic strategy to rewire behavioural circuits by engineering synaptic connectivity in C. elegans.

View Article: PubMed Central - PubMed

Affiliation: 1] Division of Cell Biology, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK [2] Department of Medical Neurobiology, Hadassah Medical School, Hebrew University of Jerusalem, Jerusalem 9112102, Israel [3].

ABSTRACT
Neural circuits are functional ensembles of neurons that are selectively interconnected by chemical or electrical synapses. Here we describe a synthetic biology approach to the study of neural circuits, whereby new electrical synapses can be introduced in novel sites in the neuronal circuitry to reprogram behaviour. We added electrical synapses composed of the vertebrate gap junction protein Cx36 between Caenorhabditis elegans chemosensory neurons with opposite intrinsic responses to salt. Connecting these neurons by an ectopic electrical synapse led to a loss of lateral asymmetry and altered chemotaxis behaviour. In a second example, introducing Cx36 into an inhibitory chemical synapse between an olfactory receptor neuron and an interneuron changed the sign of the connection from negative to positive, and abolished the animal's behavioural response to benzaldehyde. These data demonstrate a synthetic strategy to rewire behavioural circuits by engineering synaptic connectivity in C. elegans.

Show MeSH
Related in: MedlinePlus