MECP2 mutations rewire human ESC fate and bias cortical lineage commitment.

Rett syndrome arises from loss-of-function mutations in the X-linked chromatin regulator MECP2, yet the earliest molecular derailments in development are poorly defined. Using isogenic human embryonic stem cell (hESC) models carrying three patient-derived MECP2 mutations, we followed the transcriptome from pluripotency through neuroectoderm, neural stem/progenitor stages. Developmental stage dominated transcriptional variance, but mutants shared a secondary program enriched for synaptic-membrane and extracellular matrix genes. Single-cell/bulk profiling at the embryonic stem cell (ESC) stage revealed partial naïve-like drift, marked by the up-regulation of the naïve-enriched factor ZFP42/REX1 and related markers in MECP2-mutant lines. Among convergently dysregulated genes, the cortical determinant EMX1 showed an abnormal developmental trajectory, early repression followed by overshoot, and was consistently altered across independent Rett PSC models. Single-nucleus RNA-seq of cerebral organoids uncovered allele-specific yet convergent disturbances in cortical lineage allocation. These data chart a continuous developmental trajectory for MECP2-mutant cells and nominate naïve-like drift and mis-timed EMX1 expression as tractable entry points for dissecting Rett pathogenesis.