Reviewer #1 (Public Review): Self-formation of concentric zones of telencephalic and ocular tissues and directional retinal ganglion cell axons

Abstract

The telencephalon and eye in mammals are originated from adjacent fields at the anterior neural plate. Morphogenesis of these fields generates telencephalon, optic-stalk, optic-disc, and neuroretina along an axis. How these telencephalic and ocular tissues are specified coordinately to ensure directional retinal ganglion cell (RGC) axon growth is unclear. Here, we report the self-formation of human telencephalon-eye organoids comprising concentric zones of telencephalic, optic-stalk, optic-disc, and neuroretinal tissues along the center-periphery axis. Initially-differentiated RGCs grew axons towards and then along a path defined by adjacent PAX2+ optic-disc cells. Single-cell RNA sequencing identified expression signatures of two PAX2+ cell populations that mimic optic-disc and optic-stalk, respectively, mechanisms of early RGC differentiation and axon growth, and RGC-specific cell-surface protein CNTN2, leading to one-step purification of electrophysiologically-excitable RGCs. Our findings provide insight into the coordinated specification of early telencephalic and ocular tissues in humans and establish resources for studying RGC-related diseases such as glaucoma.