Minor spliceosome inactivation causes microcephaly due to cell cycle defects and death of self-amplifying radial glial cells

Abstract

Mutation in minor spliceosome components is linked to the developmental disorder microcephalic osteodysplastic primordial dwarfism type 1 (MOPD1). Here we inactivated the minor spliceosome in the developing mouse cortex (pallium) by ablating Rnu11, which encodes the crucial minor spliceosome snRNA U11. Rnu11 conditional knockout mice were born with microcephaly, which was caused by the death of self-amplifying radial glial cells (RGCs), while intermediate progenitor cells and neurons were produced. RNAseq suggested that this cell death was mediated by upregulation of p53 and DNA damage, which were both observed specifically in U11-null RGCs. Moreover, U11 loss caused elevated minor intron retention in genes regulating cell cycle, which was consistent with fewer RGCs in S-phase and cytokinesis, alongside prolonged metaphase in RGCs. In all, we found that self-amplifying RGCs are the cell type most sensitive to loss of minor splicing. Together, these findings provide a potential explanation of how disruption of minor splicing might cause microcephaly in MOPD1.