Single-cell q-PCR derived expression profiles of identified sensory neurons

Sensory neurons are chemically and functionally heterogeneous, and this heterogeneity has been examined extensively over the last several decades. These studies have employed a variety of different methodologies, including anatomical, electrophysiological, and molecular approaches. Recent studies using next-generation sequencing techniques have examined the transcriptome of single sensory neurons. Although these reports have provided a wealth of exciting new information on the heterogeneity of sensory neurons, correlation with functional types is lacking. Here, we employed retrograde tracing of cutaneous and muscle afferents to examine the variety of mRNA expression profiles of individual, target-specific sensory neurons. In addition, we used an ex vivo skin/nerve/dorsal root ganglion/spinal cord preparation to record and characterize the functional response properties of individual cutaneous sensory neurons that were then intracellularly labeled with fluorescent dyes, recovered from dissociated cultures, and analyzed for gene expression. We found that by using single-cell quantitative polymerase chain reaction techniques and a set of 28 genes, we can identify transcriptionally distinct groups. We have also used calcium imaging and single-cell quantitative polymerase chain reaction to determine the correlation between levels of mRNA expression and functional protein expression and how functional properties correlated with the different transcriptional groups. These studies show that although transcriptomics does map to functional types, within any one functional subgroup, there are highly variable patterns of gene expression. Thus, studies that rely on the expression pattern of one or a few genes as a stand in for physiological experiments, runs a high risk of data misinterpretation with respect to function.