Dysregulation of early neurodevelopment is implicated in macrocephaly/autism disorders. However, the mechanism underlying this dysregulation, particularly in human cells, remains poorly understood. Mutations in the small GTPase gene RAB39b are associated with X-linked macrocephaly, autism spectrum disorder (ASD), and intellectual disability. The in vivo roles of RAB39b in the brain remain unknown. We generated Rab39b knockout (KO) mice and found that they exhibited cortical neurogenesis impairment, macrocephaly, and hallmark ASD behaviors, which resembled patient phenotypes. We also produced mutant human cerebral organoids that were substantially enlarged due to the overproliferation and impaired differentiation of neural progenitor cells (NPCs), which resemble neurodevelopmental deficits in KO mice. Mechanistic studies reveal that RAB39b interacts with PI3K components and its deletion promotes PI3K-AKT-mTOR signaling in NPCs of mouse cortex and cerebral organoids. The mTOR activity is robustly enhanced in mutant outer radial glia cells (oRGs), a subtype of NPCs barely detectable in rodents but abundant in human brains. Inhibition of AKT signaling rescued enlarged organoid sizes and NPC overproliferation caused by RAB39b mutations. Therefore, RAB39b mutation promotes PI3K-AKT-mTOR activity and alters cortical neurogenesis, leading to macrocephaly and autistic-like behaviors. Our studies provide new insights into neurodevelopmental dysregulation and common pathways associated with ASD across species.

中文翻译：

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脑类器官和小鼠模型揭示了皮质发育的RAB39b-PI3K-mTOR通路依赖性失调，导致大头畸形/自闭症表型。

早期神经发育失调与大头畸形/自闭症有关。然而，这种失调的机制，尤其是在人类细胞中，尚不清楚。小GTPase基因RAB39b中的突变与X连锁大头畸形，自闭症谱系障碍（ASD）和智力障碍有关。RAB39b在脑中的体内作用仍然未知。我们生成了Rab39b基因敲除（KO）小鼠，发现它们表现出皮质神经发生损伤，大头畸形和标志性ASD行为，类似于患者的表型。我们还产生了突变的人类脑器官，由于过度增殖和神经祖细胞（NPCs）的分化受损而大大扩大，这类似于KO小鼠的神经发育缺陷。机理研究表明，RAB39b与PI3K组分相互作用，其缺失可促进小鼠皮质和脑类器官NPC中的PI3K-AKT-mTOR信号传导。mTOR活性在突变的外放射状神经胶质细胞（oRGs）中得到了强有力的增强，oRGs是在啮齿动物中几乎检测不到但在人脑中丰富的NPC亚型。抑制AKT信号可以挽救因RAB39b突变而导致的类器官增大和NPC过度增殖。因此，RAB39b突变促进PI3K-AKT-mTOR活性并改变皮质神经发生，导致大头畸形和自闭症行为。我们的研究为跨物种的ASD相关的神经发育失调和常见途径提供了新见解。mTOR活性在突变的外放射状神经胶质细胞（oRGs）中得到了强有力的增强，oRGs是在啮齿动物中几乎检测不到但在人脑中丰富的NPC亚型。抑制AKT信号可以挽救因RAB39b突变而导致的类器官增大和NPC过度增殖。因此，RAB39b突变促进PI3K-AKT-mTOR活性并改变皮质神经发生，导致大头畸形和自闭症行为。我们的研究为跨物种的ASD相关的神经发育失调和常见途径提供了新见解。mTOR活性在突变的外放射状神经胶质细胞（oRGs）中得到了强有力的增强，oRGs是在啮齿动物中几乎检测不到但在人脑中丰富的NPC亚型。抑制AKT信号可以挽救因RAB39b突变而导致的类器官增大和NPC过度增殖。因此，RAB39b突变促进PI3K-AKT-mTOR活性并改变皮质神经发生，导致大头畸形和自闭症行为。我们的研究为跨物种的ASD相关的神经发育失调和常见途径提供了新见解。RAB39b突变促进PI3K-AKT-mTOR活性并改变皮层神经发生，导致大头畸形和自闭症行为。我们的研究为跨物种的ASD相关的神经发育失调和常见途径提供了新见解。RAB39b突变促进PI3K-AKT-mTOR活性并改变皮层神经发生，导致大头畸形和自闭症行为。我们的研究为跨物种的ASD相关的神经发育失调和常见途径提供了新见解。