Expression profiling analysis of mouse E10.5 Magoh mutant brain cortices

Human brain structure and size requires regulated division of neural stem cells (NSCs). NSCs undergo precise divisions to self-renew and to produce intermediate neural progenitors (INPs) and neurons. The factors that regulate NSC divisions remain poorly understood, as do mechanistic explanations of how aberrant NSC division causes reduced brain size, as seen in microcephaly. Here we demonstrate that Magoh, a component of the core exon junction complex (EJC) that binds spliced RNA, controls cerebral cortical size by regulating NSC division. Magoh haploinsufficiency causes microcephaly due to INP depletion, neuronal apoptosis, and improper mitotic spindle orientation. Defective mitosis underlies these phenotypes as depletion of EJC components disrupts mitotic spindle integrity, chromosome number and genomic stability. We show that an essential function of Magoh is to regulate expression of the human microcephaly protein, LIS1, and that Lis1 addition rescues neurogenesis defects caused by Magoh knockdown, thus providing a genetic explanation for the microcephaly. This study uncovers new requirements for the EJC in brain development, NSC maintenance, mitosis and chromosome stability, thus implicating this complex in the pathogenesis of microcephaly.

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Silver DL, Watkins-Chow DE, Schreck KC, Pierfelice TJ, Larson DM, Burnetti AJ, Liaw HJ, Myung K, Walsh CA, Gaiano N, Pavan WJ