The ExDression Pattern of the Orphan Nuclear Receptor RORβ in the Developing and Adult Rat Nervous System Suggests a Role in the Processing of Sensory Information and in Circadian Rhythm

Abstract

RORβ is an orphan nuclear receptor related to retinoid and thyroid hormone receptors and is exclusively expressed in the central nervous system (CNS). Here we present an in situ hybridization analysis of the distribution of RORβ mRNA in the developing and adult rat CNS. The receptor localizes to areas involved in the processing of sensory information. In the cerebral cortex, RORβ mRNA was exclusively detected in non‐pyramidal neurons of layer IV and, less so, layer V. The highest expression was found in primary sensory cortices. In the thalamus highest RORβ expression was found in the sensory relay nuclei projecting to the respective cortical areas. In contrast, sensory projection neurons in the periphery, for example retinal ganglion cells and neurons of the sensory ganglia showed only little RORβ expression. RORβ is also expressed in areas involved in the generation and maintenance of circadian rhythms ‐ the suprachiasmatic nucleus, the pineal gland and the retina. In the latter two tissues, RORβ mRNA abundance oscillates with circadian rhythmicity peaking during the hours of darkness. RORβ rnRNA could not be detected in striatum, hippocampus, cerebellum, the motor nuclei of the cranial nerves or the ventral part of the spinal cord. During development, RORβ is expressed in many areas as early as embryonic day (E) 15, anticipating the distribution pattern in the adult. Our data suggest that RORβ regulates genes whose products play essential roles in the context of sensory input integration as well as in the context of circadian timing system.