Importantly, sensory experience is required for the formation and maintenance of the dendritic spines of these apical tuft dendrites (Holtmaat and Svoboda, 2009), and the regulation of dendritic complexity by MeCP2 S421 phosphorylation may represent a related mechanism Selleck Ku-0059436 of experience-dependent neuronal development. In
contrast to apical tuft dendrites, the complexity of basal and proximal apical dendrites did not differ significantly between the MeCP2 S421A and wild-type cells. The fact that in cortical circuits layer V pyramidal cells receive distinct types of synaptic input on their basal, proximal apical, and distal apical dendrites, together with our finding that MeCP2 S421 phosphorylation is selectively required for the patterning of the distal apical dendrites, suggests that MeCP2 phosphorylation at S421 may be critical for specific aspects of activity-dependent circuit development. Moreover, disruptions in this activity-dependent process when MECP2 is mutated may contribute to features of RTT. Given the importance of neuronal patterning for synaptic connectivity, we reasoned that the increase in dendritic complexity observed MK-8776 in vivo in the MeCP2 S421A cortex might reflect a role for activity-dependent MeCP2 phosphorylation in cortical circuit development. Although
it has been proposed that MeCP2 regulates experience-dependent aspects of synaptic maturation, the specific importance of activity-dependent regulation of MeCP2 in this context has not been demonstrated. To assess the effect of loss of MeCP2 S421 phosphorylation on synaptic development, we prepared acute slices containing primary visual cortex (V1) from the brains of postnatal day 16–17 MeCP2 S421A mice and their wild-type littermates, and obtained whole-cell patch-clamp recordings
from layer II/III pyramidal neurons. Disruption of MeCP2 expression in the cortex has indicated a general requirement for MeCP2 in cortical neuron synaptic function (Guy et al., 2010). We analyzed pyramidal cells in cortical layer II/III of postnatal Casein kinase 1 visual cortex because of the well-defined role of neuronal activity in modulating the function of these cells (Maffei and Turrigiano, 2008 and Trachtenberg et al., 2000). We analyzed pharmacologically isolated V1 layer II/III spontaneous miniature inhibitory postsynaptic currents (mIPSCs). We saw no effect on the frequency of mIPSCs obtained from these whole-cell patch-clamp recordings when wild-type and MeCP2 S421A mice were compared (Figures 3B and 3D). In contrast, the amplitude of mIPSCs recorded from MeCP2 S421A neurons in acute cortical slice were significantly increased relative to neurons from wild-type samples (Figures 3C and 3E).