Loss of CDK5RAP2 affects neural but not non-neural mESC differentiation into cardiomyocytes

Biallelic mutations in the gene encoding centrosomal CDK5RAP2 lead to autosomal recessive primary microcephaly (MCPH), a disorder characterized by pronounced reduction in volume of otherwise architectonical normal brains and intellectual deficit. The current model for the microcephaly phenotype in MCPH invokes a premature shift from symmetric to asymmetric neural progenitor-cell divisions with a subsequent depletion of the progenitor pool. The isolated neural phenotype, despite the ubiquitous expression of CDK5RAP2, and reports of progressive microcephaly in individual MCPH cases prompted us to investigate neural and non-neural differentiation of <i>Cdk5rap2</i>-depleted and control murine embryonic stem cells (mESC). We demonstrate an accumulating proliferation defect of neurally differentiating <i>Cdk5rap2</i>-depleted mESC and cell death of proliferative and early postmitotic cells. A similar effect does not occur in non-neural differentiation into beating cardiomyocytes, which is in line with the lack of non-central nervous system features in MCPH patients. Our data suggest that MCPH is not only caused by premature differentiation of progenitors, but also by reduced propagation and survival of neural progenitors.

编码定位于中心体的CDK5RAP2（centrosomal CDK5RAP2）的基因发生双等位基因突变，可导致常染色体隐性遗传性原发性小头畸形（autosomal recessive primary microcephaly, MCPH），该疾病以大脑结构正常但体积显著缩减、伴智力缺陷为核心特征。当前针对MCPH小头畸形表型的致病模型提出，其发病机制为神经前体细胞分裂过早从对称模式转向不对称模式，进而引发前体细胞库耗竭。尽管CDK5RAP2呈广泛表达，但MCPH仅表现出孤立的神经表型，且部分病例存在进行性小头畸形，这一现象促使我们探究Cdk5rap2敲低及对照组小鼠胚胎干细胞（murine embryonic stem cells, mESC）的神经与非神经分化情况。实验结果显示，神经分化过程中的Cdk5rap2敲低mESC会逐渐出现增殖缺陷，且增殖期与早期有丝分裂后细胞发生死亡。而在非神经分化为搏动性心肌细胞的实验体系中，并未出现类似效应，这与MCPH患者无中枢神经系统以外的临床表型相一致。本研究数据表明，MCPH的致病机制不仅涉及前体细胞的过早分化，还包括神经前体细胞的增殖能力与存活水平下降。