Self-assembly of cellular neighborhoods converts stochastic signaling into sustained olfactory neurogenesis

Abstract

SUMMARYOlfactory neurogenesis occurs continuously throughout the lives of vertebrates, including in humans, and relies on the rapid, unceasing differentiation and integration of neurons into a complex multicellular network. The system-wide regulation of this intricate choreography is poorly understood; in particular, it is unclear how progenitor cells convert stochastic fluctuations in cell-cell signaling, over both space and time, into streamlined fate decisions. Here, we track single-cell level multicellular dynamics in the developing zebrafish olfactory epithelium, perturb signaling pathways with temporal specificity, and find that the continuous generation of neurons is driven by the spatially-restricted self-assembly of transient groups of progenitor cells, i.e. cellular neighborhoods. Stochastic modeling and validation of the underlying genetic circuit reveals that neighborhood self-assembly is driven by a tightly regulated bistable toggle switch between Notch signaling and the transcription factor Insulinoma-associated 1a that is responsive to inter-organ retinoic acid signaling. Newly differentiating neurons emerge from neighborhoods and, in response to brain-derived neurotrophic factor signaling, migrate across the olfactory epithelium to take up residence as apically-located, mature sensory neurons. After developmental olfactory neurogenesis is complete, inducing injury results in a robust expansion of neighborhoods, followed by neuroregeneration. Taken together, these findings provide new insights into how stochastic signaling networks spatially pattern and regulate a delicate balance between progenitors and their neuronal derivatives to drive sustained neurogenesis during both development and regeneration.