Identification of the sensory neuron specific regulatory region for the mouse gene encoding the voltage-gated sodium channel NaV1.8.

Voltage-gated sodium channels (VGSC) are critical membrane components that participate in the electrical activity of excitable cells. The type one VGSC family includes the tetrodotoxin insensitive sodium channel, Na(V)1.8, encoded by the Scn10a gene. Na(V)1.8 expression is restricted to small and medium diameter nociceptive sensory neurons of the dorsal root ganglia and cranial sensory ganglia. To understand the stringent transcriptional regulation of the Scn10a gene, the sensory neuron specific promoter was functionally identified. While identifying the mRNA 5'-end, alternative splicing within the 5'-UTR was observed to create heterogeneity in the RNA transcript. Four kilobases of upstream genomic DNA was cloned and the presence of tissue specific promoter activity was tested by microinjection and adenoviral infection of fluorescent protein reporter constructs into primary mouse and rat neurons, and cell lines. The region contained many putative transcription factor-binding sites and strong homology with the predicted rat ortholog. Homology to the predicted human ortholog was limited to the proximal end and several conserved cis elements were noted. Two regulatory modules were identified by microinjection of reporter constructs into dorsal root ganglia and superior cervical ganglia neurons: a neuron specific proximal promoter region between -1.6 and -0.2 kb of the transcription start site cluster, and a distal sensory neuron switch region beyond -1.6 kb that restricted fluorescent protein expression to a subset of primary sensory neurons.