Retinoic acid signaling guides the efficiency of inner ear organoid-genesis and governs sensory-nonsensory fate specification

Inner ear organoid development-from germ layer to otic vesicle (OV) formation-relies on timed chemical cues to recapitulate major signals in vivo. In contrast, later stages of differentiation-from OV to organoid formation-are self-guided, even though these stages are modulated by several key morphogens in vivo. We sought to elucidate additional morphogens that might improve culture efficiency and influence cell fate decisions. Using a whole-transcriptomic approach, we identified major differences in native and stem-cell-derived OVs related to anterior-posterior patterning and retinoic acid (RA) signaling. Increasing the level of RA during OV formation in these cultures modulated organoid efficiency, increased nonsensory markers, decreased sensory markers, and decreased hair cell production. The organoid culture platform mimics the exquisite RA sensitivity found in normal inner ear development and provides a tunable system for generating sensory and nonsensory cell types in inner ear organoids.