Deterministic and probabilistic fate decisions co-exist in a single retinal lineage

Correct nervous system development depends on the timely differentiation of progenitor cells into neurons. While the output of progenitor differentiation is well investigated at the population and clonal level, the possibilities and constraints for fate decisions of specific progenitors over development are less explored. Particularly little is known about their variability and competence plasticity. To fill this gap, we here use long-term live imaging to follow the outcome of progenitor divisions in the zebrafish retina. We find that neurogenic Atoh7 expressing progenitors produce different neuronal types over development with time-dependent probabilities. Interestingly, deterministic and probabilistic fate decisions co-exist in the same lineage. While interference with the deterministic fate affects lineage progression, interference with fate probabilities of the stochastic lineage branch results in a broader range of fate possibilities than seen in controls. When tissue development is challenged, Atoh7 expressing progenitors can produce any neuronal type, arguing against the concept of fixed competence windows. Stochastic modelling of fate probabilities in challenged conditions revealed a simple gene regulatory network able to recapitulate the observed competence changes during development. Based on our results, we postulate that fate plasticity could be involved in robust retinal development, a concept possibly applicable to other tissues. ### Competing Interest Statement The authors have declared no competing interest.