MeCP2 dysfunction prevents proper BMP signaling and neural progenitor expansion in brain organoid

Objectives: Sporadic mutations in MeCP2 are a hallmark of Rett syndrome (RTT). Many RTT brain organoid models have exhibited pathogenic pheno-types such as decreased spine density and small size of soma with altered electrophysiological signals. However, previous models are mainly focused on the phenotypes observed in the late phase and rarely provide clues for the defect of neural progenitors which generate different types of neurons and glial cells. Methods: We newly established the RTT brain organoid model derived from MeCP2-truncated iPS cells which were genetically engineered by CRISPR/Cas9 technology. By immunofluorescence imaging, we studied the development of NPC pool and its fate specification into glutamatergic neu-rons or astrocytes in RTT organoids. By total RNA sequencing, we investi-gated which signaling pathways were altered during the early brain development in RTT organoids. Results: Dysfunction of MeCP2 caused the defect of neural rosette formation in the early phase of cortical development. In total transcriptome analysis, BMP pathway-related genes are highly associ-ated with MeCP2 depletion. Moreover, levels of pSMAD1/5 and BMP target genes are excessively increased, and treatment of BMP inhibitors partially res-cues the cell cycle progression of neural progenitors. Subsequently, MeCP2 dysfunction reduced the glutamatergic neurogenesis and induced overproduc-tion of astrocytes. Nevertheless, early inhibition of BMP pathway rescued VGLUT1 expression and suppressed astrocyte maturation. Interpretation: Our results demonstrate that MeCP2 is required for the expansion of neural pro-genitor cells by modulating BMP pathway at early stages of development, and this influence persists during neurogenesis and gliogenesis at later stages of brain organoid development.

Automated summary

This study established an RTT brain organoid model and investigated the impact of MeCP2 dysfunction on neural development and gliogenesis. It was found that MeCP2 modulates the expansion of neural progenitor cells by regulating the BMP pathway. These findings contribute to a better understanding of the pathogenesis of RTT.