RXRγ gene is expressed by discrete cell columns within the alar plate of the brainstem of the chicken embryo

With in situ hybridization assays, we mapped the distribution of retinoid X receptor γ (RXRγ) gene transcripts in the central nervous system of the chicken embryo. Previous studies have demonstrated the presence of RXRγ transcripts in migrating neural crest and in neural crest derivatives throughout the peripheral nervous system, implicating RXRγ 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 RXRγ transcripts in discrete regions of the developing neural tube, within the hindbrain, the cerebellar plate, the optic tectum, and the diencephalon. At stage 10, when migrating neural crest expresses RXRγ transcripts, we detect no transcripts in the neural tube. By stage 13, RXRγ transcripts accumulate to detectable levels along the midline of the posterior optic tectum, where the neural crest‐derived sensory neurons of the mesencephalic trigeminal nucleus are located. By stage 15, RXRγ transcripts also appear in an intermittent longitudinal cell column 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. Expression in these cell populations continues until at least stage 22.5, when many neuron populations have been generated in the hindbrain. The localization of the RXRγ‐positive cells to the mantle zone suggests that they are postmitotic and are probably neurons. Their specific alar locations indicate that they reside within sensory columns and potential downstream targets, evidently corresponding to some of the central components of the trigeminal system. J. Comp. Neurol. 416:417–428, 2000.