Targeting and in C-fiber low threshold mechanoreceptor: limitation of -IRES-.

Peripheral somatosensory neurons in the dorsal root ganglia (DRG) transduce mechanical force in the skin and other organs into electrical signals using specialized mechanically activated (MA) ion channels that initiate neuronal activation in response to force. Increasing evidence highlights PIEZO2 as the primary transducer of low-threshold mechanical force in DRG neurons. However, in the absence of , mice and humans still respond to noxious painful stimuli like pinch, suggesting that additional MA channel(s) likely exist in DRG neurons. Strategies to identify lines and DRG subpopulations that select for non-PIEZO2 expressing neurons is therefore an ongoing effort in the field to discover unknown mechanosensors. Here, we investigated a labeled mouse line as a candidate to identify non-PIEZO2 MA channels in a subtype of DRG neurons called C-fiber low threshold mechanoreceptors (C-LTMRs). Our study carefully demonstrates that the IRES mouse line specifically and efficiently labels C-LTMR neurons of the DRG. Electrophysiological recordings using two different mechanical stimulation assays show that the genetically labelled neurons have robust indentation- and stretch-activated MA currents that are exclusively slowly or ultra-slowly adapting. To determine whether the -IRES- mouse line can be used to delete genes of interest and identify the underlying MA ion channels in C-LTMRs we attempted to generate a conditional knockout using this line but detected incomplete loss of transcript and lack of TMEM63B-dependent effect on C-LTMR MA currents. Together, our results emphasize that although the IRES line is robust in driving expression of a conditional reporter gene, it is inefficient in deleting genes like as well as .