Activity-Induced MeCP2 Phosphorylation Regulates Retinogeniculate Synapse Refinement

Area of Science:

• Neuroscience
• Molecular Biology
• Developmental Biology

Background:

• Mutations in the Methyl CpG Binding Protein 2 (MECP2) gene cause Rett syndrome (RTT), a severe neurodevelopmental disorder affecting females.
• The precise mechanisms by which MECP2 dysfunction leads to RTT symptoms, particularly neural circuit miswiring, are not fully understood.
• Neuronal activity and sensory experience are known to influence brain development and synaptic plasticity.

Approach:

• Investigated the role of activity-dependent phosphorylation of MeCP2 at four specific brain residues (S86, S274, T308, S421).
• Generated a quadruple knock-in (QKI) mouse model where these phosphorylation sites were mutated to alanine, preventing phosphorylation.
• Utilized electrophysiological recordings at the retinogeniculate synapse to assess synapse elimination and maturation in QKI mice compared to wild-type and Mecp2 null mice.

Key Points:

• QKI mice, lacking activity-dependent MeCP2 phosphorylation, did not exhibit overt RTT phenotypes or significant gene expression changes.
• Electrophysiological analysis revealed normal initial synapse elimination at P14, but significantly compromised elimination at P20 in QKI mice.
• This synaptic maturation defect in QKI mice is distinct from the phenotype observed in Mecp2 null mice, suggesting a specific role for phosphorylation.

Conclusions:

• Activity-induced phosphorylation of MeCP2 is critical for the precise timing of retinogeniculate synapse maturation during early postnatal development.
• This phosphorylation-dependent mechanism is essential for proper neural circuit development and may underlie aspects of RTT pathophysiology.
• Findings highlight a novel function of MeCP2 phosphorylation in sensory experience-dependent synaptic pruning and provide insights into RTT.