RETINOID-X RECEPTOR-GAMMA GENE-EXPRESSION IS DEVELOPMENTALLY-REGULATED IN THE EMBRYONIC RODENT PERIPHERAL NERVOUS-SYSTEM

The retinoid X receptor-gamma (RXR gamma) is a transcription factor th at belongs to the thyroid hormone/retinoid family of nuclear receptors . Previous studies have shown that RXR gamma is expressed in the devel oping peripheral nervous system (PNS) of chick embryos, but such expre ssion has not been reported previously in rodent embryos. Indeed, the pattern of RXR gamma expression appears to be different between avian and rodent species. Using in situ hybridisation and northern blot expe riments we show that RXR gamma is expressed in elements of the PNS in rat and mouse embryos and in postnatal rats. However, unlike the chick , where RXR gamma is expressed from the onset of neural crest migratio n, rat RXR gamma expression in the dorsal root ganglia and trigeminal ganglia was detectable at 14.5 days post coitum (dpc), but not at 13, 12, or 11 dpc. These data suggest that RXR gamma may have a role in th e dorsal root ganglia and trigeminal ganglia of late embryos, and that this could be evolutionarily conserved between chick and rodent. On t he other hand, rat RXR gamma transcripts in the facio-acoustic (VII-VI II) ganglion were detectable at 11 dpc in neural crest cells condensin g to form this ganglion. We discuss the possible significance of the t iming of RXR gamma expression in the developing PNS and suggest that c loser examination of the structure and function of the PNS of RXR gamm a null mutant mice would be of interest.