The role of retinoic acid receptors in neurite outgrowth from different populations of embryonic mouse dorsal root ganglia.

Dorsal root ganglion (DRG) neurons can be categorised into at least three types, based upon their neurotrophin requirement for survival. We have analysed the expression of the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs) in NGF, NT-3 and BDNF dependent neurons isolated from embryonic day (E)13.5 mouse DRG. We show that each population of neurons expressed each of the three RXRs, (alpha), (beta) and (gamma); however, whilst the NGF and NT-3 dependent neurons expressed each of the RARs (alpha), (beta) and (gamma), the BDNF dependent neurons only expressed RAR(alpha) and (beta). When retinoic acid was added to each of the neuronal classes only the NGF and NT-3 dependent neurons responded by extending neurites, and this response involved the upregulation of RAR(beta)(2). This specificity was confirmed by the use of receptor-selective agonists as only a RAR(beta)-selective compound stimulated neurite outgrowth. These results suggest a role for RA acting via RAR(beta)(2) in the outgrowth of neurites.