miR-9 mediated noise optimization of the her6 oscillator is needed for cell state progression in the Zebrafish hindbrain

Ultradian oscillations of key transcription factors, such as members of the Hes family, are thought to be important in Neural Progenitor Cell (NPC) maintenance and miR-9 acts as a tuner of these oscillations in vitro. However, the existence and the role of such dynamic oscillatory expression in vivo is poorly understood. Here, we have generated a Zebrafish CRISPR knock-in Her6::venus fusion (Hes1 orthologue) to study endogenous dynamic gene expression in the embryonic hindbrain. We show that Her6 undergoes a transition from irregular, noisy, fluctuations to periodic oscillations as neurogenesis proceeds. In the absence of miR-9 input, noise in the Her6 oscillator increases and NPCs are unable to transit away from an intermediary state where they co-express progenitor and early differentiation markers. Thus, Her6 oscillations are facilitated by noise optimization mediated by miR-9 and this noise-tuning step is functionally important for cells to transition to differentiation.