Abstract
Optogenetic approaches using light-activated proteins like Channelrhodopsin-2 (ChR2) enable investigating the function of populations of neurons in live Caenorhabditis elegans (and other) animals, as ChR2 expression can be targeted to these cells using specific promoters. Sub-populations of these neurons, or even single cells, can be further addressed by restricting the illumination to the cell of interest. However, this is technically demanding, particularly in free moving animals. Thus, it would be helpful if expression of ChR2 could be restricted to single neurons or neuron pairs, as even wide-field illumination would photostimulate only this particular cell. To this end we adopted the use of Cre or FLP recombinases and conditional ChR2 expression at the intersection of two promoter expression domains, i.e. in the cell of interest only. Success of this method depends on precise knowledge of the individual promoters' expression patterns and on relative expression levels of recombinase and ChR2. A bicistronic expression cassette with GFP helps to identify the correct expression pattern. Here we show specific expression in the AVA reverse command neurons and the aversive polymodal sensory ASH neurons. This approach shall enable to generate strains for optogenetic manipulation of each of the 302 C. elegans neurons. This may eventually allow to model the C. elegans nervous system in its entirety, based on functional data for each neuron.
Highlights
Optogenetic approaches to control cellular activity are increasingly used in the neurosciences, to decipher the function of neuronal populations within neuronal circuits or to precisely control synaptic transmission and/or plasticity [1,2,3,4,5]
In few cases in C. elegans, single-cell specific promoters have been described that may be employed, but these are rare, and their utility can be limited as the achievable expression levels may be too low
Promoter pairs potentially overlapping in this cell, or in any given neuron, can be deduced from the literature, i.e. as data deposited in wormbase, and conveniently summarized for each cell in Nikhil Bathla’s online tool ‘‘C. elegans interactive neural network’’
Summary
Optogenetic approaches to control cellular activity are increasingly used in the neurosciences, to decipher the function of neuronal populations within neuronal circuits or to precisely control synaptic transmission and/or plasticity [1,2,3,4,5]. Light-activated enzymes like photoactivated adenylate cyclase (PAC) [10,11,12] to stimulate intracellular 2nd messenger signaling, photoswitchable protein tags like the LOV domain or phototriggered protein-protein interaction modules are used [13,14]. These proteins are generally expressed using cell-type specific promoters, e.g. those of vesicular acetylcholine- or GABA transporters, to restrict them to certain neuronal populations [4]. This could even enable ‘‘functional mapping’’ of the C. elegans nervous system in a neuron-by-neuron manner
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