Cerebral organoid and mouse models reveal a RAB39b-PI3K-mTOR pathway-dependent dysregulation of cortical development leading to macrocephaly/autism phenotypes

Genes Dev. 2020 Apr 1;34(7-8):580-597. doi: 10.1101/gad.332494.119. Epub 2020 Feb 27.


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.

Keywords: PI3K–AKT–mTOR; RAB39b; autism-like behaviors; cerebral organoid; macrocephaly; mice; neural progenitor cell.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Autistic Disorder / genetics*
  • Autistic Disorder / physiopathology
  • Behavior, Animal / physiology
  • Cell Differentiation / genetics
  • Cell Proliferation / genetics
  • Cerebral Cortex / cytology
  • Cerebral Cortex / embryology*
  • Gene Deletion
  • Humans
  • Megalencephaly / genetics*
  • Megalencephaly / physiopathology
  • Mice
  • Mice, Knockout
  • Models, Animal
  • Neurogenesis / genetics*
  • Organoids / cytology
  • Phosphatidylinositol 3-Kinases / metabolism
  • Signal Transduction / genetics
  • Stem Cells / cytology
  • TOR Serine-Threonine Kinases / metabolism
  • rab GTP-Binding Proteins / genetics*
  • rab GTP-Binding Proteins / metabolism


  • TOR Serine-Threonine Kinases
  • RAB39B protein, mouse
  • Rab39B protein, human
  • rab GTP-Binding Proteins