Single-cell multiome profiling reveals neuronal bias of modulatory role of MeCP2 phosphorylation.

MeCP2 is subject to many post-translational modifications, such as phosphorylation, in response to diverse stimuli. Several MeCP2 phosphorylation sites have been identified and studied individually. However, the combinatorial effect of phosphorylation at multiple sites has not been directly examined. Building on previous studies characterizing single mutations of MeCP2 phosphorylation sites, we created a mouse model carrying two mutations, serine 80 to alanine and serine 421 to glutamic acid (S80A;S421E, or A;E), in which the MeCP2 protein phosphorylation is fixed in a state observed in active neurons. A battery of behavioral tests was conducted to characterize the functional outcomes at the whole animal level, followed by two independent single-cell/nuclei level multiome profiling assays to characterize altered molecular pathways, and regulatory pattern biased towards glutamatergic neurons on both transcription and chromatin level. While integrated analysis of the multi-dimensional datasets identified cell-type specific molecular targets regulated by MeCP2 phosphorylation, the spatially resolved transcription profiling offered an orthogonal platform for target validation and provided additional information from spatial perspective. Together, results from this study revealed that the combinatorial effect of MeCP2 S80 and S421 phosphorylation is not merely synergistic, and the regulatory is biased towards glutamatergic excitatory neurons. More importantly, our study is the first to explore the single-cell multiomics profile changes in a MeCP2 phosphor mutant model and link it to the functional outcomes.