Mutations in MeCP2, which encodes a protein that has been proposed to function as a global transcriptional repressor, are the cause of Rett syndrome (RT T), an X-linked progressive neurological disorder. Although the selective inactivation of MeCP2 in neurons is sufficient to confer a Rett-like phenotype in mice, the specific functions of MeCP2 in postmitotic neurons are not known. We find that MeCP2 binds selectively to BDNF promoter III and functions to repress expression of the BDNF gene. Membrane depolarization triggers the calcium-dependent phosphorylation and release of MeCP2 from BDNF promoter III, thereby facilitating transcription. These studies indicate that MeCP2 plays a key role in the control of neuronal activity-dependent gene regulation and suggest that the deregulation of this process may underlie the pathology of RT T.

Mutations or duplications in MECP2 cause Rett and Rett-like syndromes, neurodevelopmental disorders characterized by mental retardation, motor dysfunction, and autistic behaviors. MeCP2 is expressed in many mammalian tissues and functions as a global repressor of transcription; however, the molecular mechanisms by which MeCP2 dysfunction leads to the neural-specific phenotypes of RTT remain poorly understood. Here, we show that neuronal activity and subsequent calcium influx trigger the de novo phosphorylation of MeCP2 at serine 421 (S421) by a CaMKII-dependent mechanism. MeCP2 S421 phosphorylation is induced selectively in the brain in response to physiological stimuli. Significantly, we find that S421 phosphorylation controls the ability of MeCP2 to regulate dendritic patterning, spine morphogenesis, and the activity-dependent induction of Bdnf transcription. These findings suggest that, by triggering MeCP2 phosphorylation, neuronal activity regulates a program of gene expression that mediates nervous system maturation and that disruption of this process in individuals with mutations in MeCP2 may underlie the neural-specific pathology of RTT.