STAT3 regulates the generation of astroglia in human brain organoids with high mTORC1 activity

During brain development, neural progenitor cells first produce neurons, then astrocytes and other glial cell types, which provide important trophic support and shape neuronal development and function. Intrinsic genetic programs interact with extracellular signals to control progenitor fate, resulting in temporally segregated periods of neurogenesis and gliogenesis. Animal models have implicated STAT3 as an important driver of astrogenesis; however, the signaling pathways that control glial differentiation during human brain development are less well understood. Prior work demonstrated that constitutive activation of mTORC1 signaling in human brain organoid models resulted in the precocious generation of glial-lineage cells. In this study, we tested whether mTORC1 acts via STAT3 to control astrogenesis in brain organoids. We show that knockdown of STAT3 reduces astrogenesis in wild-type organoids and in organoids with constitutively high mTORC1 signaling caused by deletion of the negative regulator TSC2. However, mTORC1 is not required for cytokine-induced activation of STAT3 and expression of the astrocytic protein GFAP. Together, these results show that mTORC1 acts through STAT3 to control astroglia production in human brain organoid models, but that mTOR signaling is dispensable for STAT3-driven astrogenesis. Summary statement Deb et al, use human brain organoid models to show a requirement for STAT3 downstream of mTORC1 in regulating astrogliogenesis during early human brain development. ### Competing Interest Statement The authors have declared no competing interest.