MeCP2 (methyl-CpG binding protein 2) functions as a molecular linker between DNA methylation, chromatin remodeling, and transcription regulation. Mutations in the X-linked human MECP2 gene cause Rett syndrome (RTT), an autism spectrum disorder that predominantly affects females. To understand the molecular mechanism of RTT, it is important to study how MeCP2 dynamically regulates gene transcription and to reveal the physiological significance of such regulation. Recent biochemical analysis has identified 8 phosphorylation sites on the MeCP2 protein. Among these, serine 80 (S80) is phosphorylated in resting neurons but dephosphorylated in active neurons, whereas serine 421 (S421) is dephosphorylated in resting neurons but phosphorylated in active neurons. Differential phosphorylation of MeCP2 in response to neuronal activity may serve as a molecular switch in dynamically modulating neuronal gene expression, leading to important consequences in development and function of the adult brain. To test this hypothesis in vivo, several novel Mecp2 knock-in alleles carrying point mutations that either abolish or mimic phosphorylation at S80 and S421 on the MeCP2 protein have been generated. As a part of a long-term goal to understand the dynamic role of MeCP2 in DNA methylation-dependent epigenetic regulation of mammalian brain development and functions, this project will study the effects of manipulating MeCP2 phosphorylation on animal behavior, study the effects of manipulating MeCP2 phosphorylation on adult neurogenesis, and study how MeCP2 phosphorylation regulates its binding to the brain-derived neurotrophic factor (Bdnf) promoter, remodels chromatin and subsequently alters BDNF expression and neuronal activity. Together, these experiments will provide insights into the central role of neuronal activity-induced differential phosphorylation of MeCP2 in regulating neuronal gene expression and its functional significance in neuronal development and animal behavior.