Region-specific Brain Targets Drive Circuit Formation and Maturation of Human Retinal Ganglion Cells
Human vision relies on retinal ganglion cells (RGCs), and their connectivity with distinct brain regions enables higher order visual processing. RGCs vary considerably between species, and many model organisms display distinct RGC types and innervation patterns from those in humans. There is thus a need for robust models of human RGC circuit formation that preserves innervation specificity. Here, we developed an in vitro microfluidics eye-to-brain connectivity model using human pluripotent stem cell (hPSC)-derived RGCs to assess brain region-specific connectivity features. We found that cultured human RGCs segregate their dendrites and axons and display axonal features that align with those of their in vivo human RGC counterparts. To identify brain target surrogates, we conducted bioinformatic similarity assessments, which revealed high conservation and lower variability between human LGN and mouse counterparts relative to available thalamocortical organoids. We thus provided region-specific mouse visual targets to assess specificity and activity. We found that human RGC axons terminals differentially connected with distinct mouse retinorecipient brain regions and promoted region-specific neural activity. Increased synapse formation occurred between RGCs and lateral geniculate neurons relative to that with suprachiasmatic nucleus neurons, modeling retina brain connectivity differences. Both retinorecipient partners induced the formation of more synapses relative to non-retinorecipient brain target controls. These results suggest that human RGC innervation properties are preserved in culture systems and that human RGCs can differentially sense and respond to retinorecipient targets to control wiring outcomes. These systems may aid in the discovery of wiring factors for potential therapeutic applications. Significance StatementThis study presents a novel in vitro model to investigate human retinal ganglion cell (RGC) connectivity, using human pluripotent stem cell-derived RGCs and specific mouse brain targets. By modeling eye-to-brain connections in a microfluidics device, we reveal that cultured human RGCs can form selective, region-specific synapses with mouse-derived brain areas like the lateral geniculate nucleus and the suprachiasmatic nucleus. The findings demonstrate that human RGCs retain their innervation specificity presences in culture, mimicking in vivo human connectivity patterns. This model thus provides a powerful tool for understanding the factors controlling human-specific brain wiring, with potential applications in therapies for visual and neurological disorders.