Genetic diseases involving overactivation of the mechanistic target of rapamycin (mTOR) pathway, so-called “mTORopathies,” often manifest with malformations of cortical development (MCDs), epilepsy, and cognitive impairment. How mTOR pathway hyperactivation results in abnormal human cortical development is poorly understood. To study the effect of mTOR hyperactivity on early stages of cortical development, we focused on Pretzel Syndrome (polyhydramnios, megalencephaly, symptomatic epilepsy; PMSE syndrome), a rare mTORopathy caused by homozygous germline mutations in the STRADA gene. We developed a human cortical organoid (hCO) model of PMSE and examined morphology and size for the first 2 weeks of organoid growth, and cell type composition at weeks 2, 8, and 12 of differentiation. In the second week, PMSE hCOs enlarged more rapidly than controls and displayed an abnormal Wnt pathway-dependent increase in neural rosette structures. PMSE hCOs also exhibited delayed neurogenesis, decreased subventricular zone progenitors, increased proliferation and cell death, and an abnormal architecture of primary cilia. At week 8, PMSE hCOs had fewer deep layer neurons. By week 12, neurogenesis recovered in PMSE organoids, but they displayed increased outer radial glia, a cell type thought to contribute to the expansion of the human cerebral cortex. Together, these findings suggest that megalencephaly in PMSE arises from the expansion of neural stem cells in early corticogenesis and potentially also from increased outer radial glial at later gestational stages. The delayed neuronal differentiation in PMSE organoids demonstrates the important role the mTOR pathway plays in the maintenance and expansion of the stem cell pool.

中文翻译：

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STRADA 突变的人类皮质类器官模拟巨脑畸形并表现出延迟的神经元分化

涉及雷帕霉素机制靶点 (mTOR) 通路过度激活的遗传疾病，即所谓的“mTOR 病变”，通常表现为皮质发育畸形 (MCD)、癫痫和认知障碍。mTOR 通路过度激活如何导致人类皮质发育异常尚不清楚。为了研究 mTOR 过度活跃对皮质发育早期阶段的影响，我们专注于 Pretzel 综合征（羊水过多、巨脑畸形、症状性癫痫；PMSE 综合征），这是一种由STRADA中纯合子系突变引起的罕见 mTOR 病变基因。我们开发了 PMSE 的人类皮质类器官 (hCO) 模型，并检查了类器官生长前 2 周的形态和大小，以及分化第 2、8 和 12 周的细胞类型组成。在第二周，PMSE hCOs 比对照组扩大得更快，并且在神经玫瑰花结结构中表现出异常的 Wnt 通路依赖性增加。PMSE hCOs 还表现出神经发生延迟、脑室下区祖细胞减少、增殖和细胞死亡增加以及原发性纤毛结构异常。在第 8 周，PMSE hCO 的深层神经元较少。到第 12 周，PMSE 类器官中的神经发生恢复，但它们表现出增加的外放射状胶质细胞，这种细胞类型被认为有助于人类大脑皮层的扩张。一起，这些研究结果表明，PMSE 中的巨脑畸形源于早期皮质生成中神经干细胞的扩张，也可能源于妊娠后期外放射状胶质细胞的增加。PMSE 类器官中延迟的神经元分化表明 mTOR 通路在干细胞库的维持和扩张中起重要作用。