Abstract
The primary somatosensory cortex in rodents contains prominent somatotopic structures called “barrels” that represent the facial whiskers. It is thought that this highly-developed structure contributes to the high sensory acuity of the whisker system. Despite that the barrel cortex has been intensively studied for almost five decades, little is known about how barrels develop in the cortex. We identified an orphan nuclear receptor, retinoid-related orphan receptor beta (RORβ), as a factor required for proper barrel development. In RORβ knockout animals, thalamocortical afferents have reduced segregation, and the postsynaptic clustering of cortical neurons is also disrupted. Intriguingly, this phenotype progresses as the knockout animals become older. Utilizing the Cre-lox system, we found that the cortex-specific RORβ conditional knockout animals recapitulated the barrel phenotype of the global knockout animals, while the thalamus-specific conditional knockout animals did not have any apparent deficit in the barrel field. In all, these results indicate that RORβ plays a key role in both the formation and the maintenance of the barrel structures. Because RORβ is required in cortical but not thalamic neurons, feedback signals from cortical neurons to their thalamic afferents are likely involved in these processes.