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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. Graphical abstract Highlights•MECP2 mutations induce an early naïve-like transcriptional drift in hESCs•EMX1 shows a conserved abnormal developmental trajectory across Rett models•Shared transcriptional programs emerge during neural induction in MECP2 mutants•Rett cerebral organoids display mutation-specific shifts in lineage allocation In this article, Flamier and colleagues show that MECP2 mutations perturb human neurodevelopment from the pluripotent stage onward. Using isogenic hESC and organoid models, they identify an early naïve-like transcriptional drift, abnormal EMX1 timing, and convergent defects in cortical lineage allocation, revealing continuous developmental vulnerability in Rett syndrome.

Maturation of human pluripotent stem (hPS) cell-derived cardiomyocytes is critical for their use as a model system. Here we mimic human heart maturation pathways in the setting of hPS cell-derived cardiac organoids (hCOs). Specifically, transient activation of 5′ AMP-activated protein kinase and estrogen-related receptor enhanced cardiomyocyte maturation, inducing expression of mature sarcomeric and oxidative phosphorylation proteins, and increasing metabolic capacity. hCOs generated using the directed maturation protocol (DM-hCOs) recapitulate cardiac drug responses and, when derived from calsequestrin 2 ( CASQ2 ) and ryanodine receptor 2 ( RYR2 ) mutant hPS cells exhibit a pro-arrhythmia phenotype. These DM-hCOs also comprise multiple cell types, which we characterize and benchmark to the human heart. Modeling of cardiomyopathy caused by a desmoplakin ( DSP ) mutation resulted in fibrosis and cardiac dysfunction and led to identifying the bromodomain and extra-terminal inhibitor INCB054329 as a drug mitigating the desmoplakin-related functional defect. These findings establish DM-hCOs as a versatile platform for applications in cardiac biology, disease and drug screening. Subject terms: Tissue engineering, Differentiation, Cardiomyopathies

Prenatal nicotine exposure impairs fetal cortical grey matter volume, but the precise cellular mechanisms remain poorly understood. This study elucidates the role of nicotinic acetylcholine receptors (nAChRs) in progenitor cells and radial glia (RG) during human cortical development. We identify two nAChR subunits—CHRNA7 and the human-specific CHRFAM7A—expressed in SOX2+ progenitors and neurons, with CHRFAM7A particularly enriched along RG endfeet. nAChR activation in organotypic slices and dissociated cultures increases RG proliferation while decreasing neuronal differentiation, whereas nAChR knockdown reduces RG and increases neurons. Single-cell RNA sequencing reveals that nicotine exposure downregulates key genes in excitatory neurons (ENs), with CHRNA7 or CHRFAM7A selectively modulating these changes, suggesting an evolutionary divergence in regulatory pathways. Furthermore, we identify YAP1 as a critical downstream effector of nAChR signaling, and inhibiting YAP1 reverses nicotine-induced phenotypic alterations in oRG cells, highlighting its role in nicotine-induced neurodevelopmental pathophysiology. Subject terms: Neuronal development, Developmental neurogenesis, Neural stem cells