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.

编码中心体CDK5RAP2的基因发生双等位基因突变，可引发常染色体隐性遗传性原发性小头畸形（autosomal recessive primary microcephaly, MCPH）——该疾病以脑体积显著缩小但组织结构正常、伴智力障碍为核心特征。目前针对MCPH小头畸形表型的致病模型认为，其发病机制为神经祖细胞从对称分裂向不对称分裂过早转换，继而导致祖细胞库耗竭。尽管CDK5RAP2在全身组织中广泛表达，但该疾病仅表现出孤立性神经表型，且部分MCPH病例存在进行性小头畸形；上述现象促使我们探究<i>Cdk5rap2</i>基因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。本研究证实，经神经分化的<i>Cdk5rap2</i>敲低mESC出现进行性增殖缺陷，且增殖期与早期有丝分裂后细胞发生死亡。而在非神经分化为可搏动心肌细胞的过程中，并未出现类似效应，这与MCPH患者无中枢神经系统（central nervous system, CNS）以外的临床特征相符。我们的研究数据表明，MCPH的致病机制不仅包括祖细胞过早分化，还涉及神经祖细胞的增殖能力与存活水平下降。