Generation, differentiation, and potential of three radial glial subtypes in human cortical organoids

Radial glia are the principal neural stem cells in the developing human cerebral cortex and have been classified as three molecularly distinct subtypes: ventricular radial glia (vRG), outer radial glia (oRG), and truncated radial glia (tRG). Human cortical organoids (hCOs) from human pluripotent stem cells that recapitulate the developmental program of the human cortex have shown this progenitor diversity. vRG and oRG are readily generated and identified in hCOs from most differentiation protocols with oRG emergence dependent on specific signaling pathways, such as LIF/STAT3 supplementation. However, tRGs that have only recently been defined at the molecular level have not been systematically examined in any organoid system. Here we review the biology, signaling, and lineage potential of each radial glial subtype and assess how faithfully they are represented in cortical organoids. We highlight and discuss the studies on the tRG from hCOs. We discuss data consistent with latent tRG competence in hCOs, including ependymal cell generation from radial glia within organoids, CRYAB-positive progenitors in three-dimensional culture systems, and tRG-associated transcriptomic shifts upon genetic perturbation, while noting that definitive tRG identification has not yet been achieved. However, definitive identification through combinatorial marker co-expression and morphological validation has not yet been achieved. Faithfully establishing molecular signatures and signaling frameworks for tRG and their existence in hCOs will provide the foundation for systemically investigating and function of this cell type in vitro, and we discuss future directions for resolving whether tRG are generated during the neurogenesis-to-gliogenesis transition. [BMB Reports 2026; 59(8): 373-383].