RXR gamma gene is expressed by discrete cell columns within the alar plateof the brainstem of the chicken embryo

With in situ hybridization assays, we mapped the distribution of retinoid X receptor gamma (RXR gamma) gene transcripts in the central nervous system of the chicken embryo. Previous studies have demonstrated the presence of R XR gamma transcripts in migrating neural crest and in neural crest. derivat ives throughout the peripheral nervous system, implicating RXR gamma as an early pan-neural crest marker (Rowe et al. 1991. Development 111:771-778), and in the retina (Hoover et al. 1998. J Comp Neurol 391:204-213). Here we report the presence of RXR gamma transcripts in discrete regions of the dev eloping neural tube, within the hindbrain, the cerebellar plate, the optic tectum, and the diencephalon. At stage 10, when migrating neural crest expr esses RXR gamma transcripts, we detect no transcripts in the neural tube. B y stage 13, RXR gamma transcripts accumulate to detectable levels along the midline of the posterior optic tectum, where the neural crest-derived sens ory neurons of the mesencephalic trigeminal nucleus are located. By stage 1 5, RXR gamma transcripts also appear in an intermittent longitudinal cell c olumn within the mantle zone of the alar plate of the hindbrain, eventually extending into the cerebellar plate rostrally and into the cervical spinal cord caudally, with a gap at about rhombomere 3. By stage 19, transcripts appear in a discrete population of cells within the diencephalon. Expressio n in these cell populations continues until at least stage 22.5, when many neuron populations have been generated in the hindbrain. The localization o f the RXR gamma-positive cells to the mantle zone suggests that they are po stmitotic and are probably neurons. Their specific alar locations indicate that they reside within sensory columns and potential downstream targets, e vidently corresponding to some of the central components of the trigeminal system. (C) 2000 Wiley-Liss, Inc.