INDUCTION OF A SEROTONERGIC AND NEURONAL PHENOTYPE IN THYROID C-CELLS

We have investigated whether rat thyroid C-cells can acquire a phenoty pe similar to serotonergic neurons. C-cells are neural crest derived e ndocrine cells with some intrinsic neuronal and serotonergic propertie s. A relatively simple isolation scheme yielded cultures of about 50% initial purity, as measured by fluorescence activated cell sorting. Th ese enriched C-cells could extend neurites up to 550 mu m on a laminin -containing substratum in the presence of NGF. The cultured C-cells ex pressed neurofilaments and this expression was enhanced by NGF treatme nt. The C-cells also expressed two markers of the sympathoadrenal neur al crest lineage, the mammalian achaete scute homolog-1 (MASH-1) trans cription factor, and the B2 cell surface antigen. Interestingly, MASH- 1 was not detectable after the C-cells were placed in culture, which i s consistent with neuronal differentiation, since MASH-1 is only expre ssed in neuronal progenitors prior to differentiation. We then demonst rated that C-cells possess the fundamental features of serotonergic ne urons: synthesis and secretion, uptake, and feedback control. The enri ched C-cells, as well as the CA77 C-cell line, showed 5-HT immunostain ing, expression of tryptophan hydroxylase mRNA, 5-HT1B autoreceptor mR NA, and 5-HT transporter mRNA and activity, NGF greatly induced 5-HT t ransporter activity as determined by sensitivity to sertraline, a sele ctive 5-HT reuptake inhibitor. Based on these results, we propose that thyroid C-cells are derived from a vagal sympathoadrenal progenitor, similar to serotonergic enteric neurons, and can undergo neuronal tran sdifferentiation. Hence, these cells should provide suitable and conve nient models for molecular and cellular studies on serotonergic neuron s.