NaG: a sodium channel-like mRNA shared by Schwann cells and other neural crest derivatives.

NaG, a member of subfamily 2, was originally characterized as a "glial" sodium channel, and is expressed at high levels in Schwann cells in vivo. However, NaG has also been shown by in situ hybridization to be highly expressed in rat dorsal root ganglion (DRG) neurons, which, like Schwann cells, are neural crest derivatives. In the present study, we used non-isotopic in situ hybridization with a riboprobe for NaG, in conjunction with RT-PCR, to determine whether NaG is expressed in tissues related to the DRG either by neural crest origin or sensory function. We found that the expression of significant levels of NaG mRNA was restricted to derivatives of the neural crest (neurons of DRG, trigeminal ganglion and mesencephalic nucleus of the trigeminal nerve, and Schwann and satellite cells); the absence of NaG from superior cervical ganglion neurons and adrenal medulla chromaffin cells indicates that not all neural crest derived neural elements express NaG. NaG was not observed in sensory neurons (retina, vestibular ganglion, spiral ganglion, olfactory epithelium) that are not of neural crest origin. Our results indicate that NaG mRNA is expressed not only in Schwann cells, but also in a spectrum of neuronal cell types with afferent function of neural crest origin. NaG thus appears to represent a transcript encoding a sodium channel or sodium channel-like protein that is uniquely expressed by both Schwann cells and afferent neurons of neural crest origin.