Brain size and cellular heterogeneity are tightly regulated by species-specific proliferation and differentiation of multipotent neural progenitor cells (NPCs). Errors in this process are among the mechanisms of primary hereditary microcephaly (MCPH), a group of disorders characterized by reduced brain size and intellectual disability. Biallelic citron rho-interacting serine/threonine kinase (CIT) missense variants that disrupt kinase function (CIT^KI/KI) and frameshift loss-of-function variants (CIT^FS/FS) are the genetic basis for MCPH17; however, the function of CIT catalytic activity in brain development and NPC cytokinesis is unknown. Therefore, we created the Cit^KI/KI mouse model and found that it did not phenocopy human microcephaly, unlike biallelic Cit^FS/FS animals. Nevertheless, both Cit models exhibited binucleation, DNA damage, and apoptosis. To investigate human-specific mechanisms of CIT microcephaly, we generated CIT^KI/KI and CIT^FS/FS human forebrain organoids. We found that CIT^KI/KI and CIT^FS/FS organoids lost cytoarchitectural complexity, transitioning from pseudostratified to simple neuroepithelium. This change was associated with defects that disrupted the polarity of NPC cytokinesis, in addition to elevating apoptosis. Together, our results indicate that both CIT catalytic and scaffolding functions in NPC cytokinesis are critical for human corticogenesis. Species differences in corticogenesis and the dynamic 3D features of NPC mitosis underscore the utility of human forebrain organoid models for understanding human microcephaly.

中文翻译：

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用人脑类器官对原发性小头畸形进行建模揭示了 CIT 激酶活性的基本作用


大脑大小和细胞异质性受到多能神经祖细胞 （NPC） 的物种特异性增殖和分化的严格调节。这个过程中的错误是原发性遗传性小头畸形 （MCPH） 的机制之一，MCPH 是一组以大脑尺寸减小和智力障碍为特征的疾病。破坏激酶功能的双等位基因柚子相互作用丝氨酸/苏氨酸激酶 （CIT） 错义变异 （CIT^KI/KI） 和移码功能丧失变异 （CIT^FS/FS） 是 MCPH17 的遗传基础;然而，CIT 催化活性在大脑发育和 NPC 胞质分裂中的功能尚不清楚。因此，我们创建了 Cit^KI/KI 小鼠模型，发现与双等位基因 Cit^FS/FS 动物不同，它不会表型复制人类小头症。然而，两种 Cit 模型都表现出双核化、DNA 损伤和细胞凋亡。为了研究 CIT 小头畸形的人类特异性机制，我们生成了 CIT^KI/KI 和 CIT^FS/FS 人前脑类器官。我们发现 CIT^KI/KI 和 CIT^FS/FS 类器官失去了细胞结构复杂性，从伪复层转变为简单的神经上皮。除了提高细胞凋亡外，这种变化还与破坏 NPC 胞质分裂极性的缺陷有关。总之，我们的结果表明 NPC 胞质分裂中的 CIT 催化和支架功能对人类皮质生成至关重要。皮质生成的物种差异和 NPC 有丝分裂的动态 3D 特征强调了人类前脑类器官模型在理解人类小头畸形方面的效用。