Abstract In the developing nervous system, highly polarized and elongated cells exhibit spatial segregation of cellular functions. This is exemplified by radial glia cells (RGCs), which are the neural stem cells that generate neurons and glia in the developing cerebral cortex. RGCs have a basal process extending hundreds of micrometers in mice, or centimeters in humans, to form basal endfeet at the pia. These basal endfeet reside in a distinct niche composed of meninges, excitatory and inhibitory neurons. Notably endfeet are proposed to act as antennas relaying signals. Endfoot integrity is essential for neuronal organization and is linked to several neurodevelopmental disorders. Yet, despite their importance, remarkably little is known about this subcellular compartment of radial glia and its role in signaling at the niche. This proposal aims to elucidate fundamental mechanisms by which RGCs signal and organize the pial niche during brain development. We focus on our recent discovery that mRNAs are actively transported within RGCs, and localized to endfeet where they can be locally translated. In the first funding cycle of this grant, we discovered endfeet contain a rich local transcriptome and subcellular proteome. Functional interrogation of four localized transcripts showed converging requirements for RGC morphology and interneuron organization. We also developed new tools to propel our understanding of how RNA localization and local translation influences RGCs. Together, this establishes a novel tractable in vivo paradigm for investigating local gene regulation in vivo during cortical neurogenesis. In this proposal we will implement our new molecular tools and apply our unique expertise to address 3 interrelated questions: 1) What is the molecular composition of RGC endfeet across development and how does this diverge in mouse and human brains? 2) How does local translation in RGCs impact signaling at the niche? 3) How is local information relayed within RGC basal structures? Successfully completed, we will have significantly advanced our understanding of fundamental molecular mechanisms of cortical neurogenesis, and specifically how subcellular compartments of neural stem cells mediate local gene expression and signaling. More broadly, we will gain insights into mRNA localization and translation in the developing nervous system.