Minor spliceosome inactivation in the developing mouse cortex causes self-amplifying radial glial cell death and microcephaly.

Inactivation of the minor spliceosome has been linked to microcephalic osteodysplastic primordial dwarfism type 1 (MOPD1). To interrogate how minor intron splicing regulates cortical development, we employed Emx1-Cre to ablate Rnu11, which encodes the minor spliceosome-specific U11 small nuclear RNA (snRNA), in the developing cortex (pallium). Rnu11 cKO mice were born with microcephaly, caused by death of self-amplifying radial glial cells (RGCs). However, both intermediate progenitor cells (IPCs) and neurons were produced in the U11-null pallium. RNAseq of the pallium revealed elevated minor intron retention in the mutant, particularly in genes regulating cell cycle. Moreover, the only downregulated minor intron-containing gene (MIG) was Spc24, which regulates kinetochore assembly. These findings were consistent with the observation of fewer RGCs entering cytokinesis prior to RGC loss, underscoring the requirement of minor splicing for cell cycle progression in RGCs. Overall, we provide a potential explanation of how disruption of minor splicing might cause microcephaly in MOPD1. RNA-seq on 5 control and 5 U11 mutant E12 dorsal telencephalon.次要剪接体（minor spliceosome）的失活已被证实与小头性骨发育不全性原始侏儒症1型（MOPD1）相关。为探究次要剪接体的剪接过程如何调控大脑皮层发育，我们利用Emx1-Cre重组酶系统在发育中的背侧端脑皮层原基（pallium）内敲除Rnu11基因——该基因编码次要剪接体特异性的U11小核RNA（small nuclear RNA，snRNA）。Rnu11条件性敲除（cKO）小鼠出生即表现小头畸形，该表型由自我扩增型放射状胶质细胞（radial glial cells，RGCs）的死亡所导致。不过，在U11缺失的皮层原基中，中间前体细胞（intermediate progenitor cells，IPCs）与神经元均能正常生成。 对皮层原基的RNA测序（RNA-seq）分析显示，突变体中次要内含子保留水平显著升高，尤其在调控细胞周期的基因群体中更为突出。此外，唯一被下调的含次要内含子基因（minor intron-containing gene，MIG）为Spc24，该基因负责调控动粒组装。上述发现与RGCs丢失前进入胞质分裂期的细胞数量减少的观测结果一致，进一步凸显了次要剪接在RGCs细胞周期进程中的必需性。综上，本研究为次要剪接紊乱如何诱发MOPD1患者的小头畸形提供了潜在的机制解释。 本研究对5只对照小鼠与5只U11突变体小鼠的胚胎12天（E12）背侧端脑组织开展了RNA-seq测序。