| The sensory neurons located in the dorsal root ganglion(DRG)are highly specific and diverse.Attributable to the expression of specific sensory ion channels and receptors,different types of DRG neurons are involved in the generation of distinct sensations.Consistant with the specific functions,their peripheral projections are also specific.Revealing the peripheral projections of different types of sensory neurons provides important insights in understanding the regulatory mechanisms of neuronal development and function.According to the sensory neuron classification determined by Usoskin D et al.using large-scale single-cell RNA sequencing assay,MrgprA3,SST and VGluT3 were selected as specific markers for non-peptidergic NP2 and NP3groups,and TH group of C-fiber low-threshold mechanical receptors,respectively.Three lines of knock-in Cre mice in which Cre recombinase was driven by the promotor of each marker gene,were crossed with Rosa26 ~LSL-PLAPSL-PLAP or Rosa26 ~LSL-tdTomatoSL-tdTomato reporter mice,and the distributions of PLAP or red fluorescent protein in skin,visceral organs or skeletal muscle were detected by histochemistry or fluorescence imaging.In addition,another marker gene,PtgIr,was found to label NF3 and PEP2group of neurons with dynamic expression during development.Adeno-associated virus(AAV)carrying mCherry reporter were intrathecally injected in adult PtgIr-Cre mice to real-time label the PtgIr-expressing neurons in adult stage,and their peripheral projections were also determined in this study.The results showed that MrgprA3~+nerve fibers dominantly projected to skin.SST~+fibers were observed in skin,multiple visceral organs and skeletal muscle,and VGluT3~+nerve fibers were detected in skin and visceral organs,while PtgIr~+fibers were completely absent in skin.These results provide further evidence supporting the high diversity of sensory neurons,and more insights to reveal their specific functions in sensation. |
