Neuron-radial glial cell communication via BMP/Id1 signaling maintains the regenerative capacity of the adult zebrafish telencephalon

The mechanisms of the management of the neural stem cell (NSC) pool underlying the regenerative capacity of the adult zebrafish brain are not understood. We show that Bone Morphogenetic Proteins (BMPs) which are exclusively expressed by neurons in the adult telencephalon and the helix-loop-helix (HLH) transcription co-regulator, Inhibitor of differentiation 1 (Id1), control quiescence of NSCs. Upon injury, lack of id1 function leads to an initial over-proliferation and subsequent loss of NSCs and the regenerative capacity. BMP/Id1 signaling up-regulates the transcription factor her4.1 which is also a target of Notch signaling mediating short-range control of NSC quiescence. Hence, the two signaling systems converge onto Her4.1. Our data show that neurons feedback on NSC proliferation. BMP1/Id1 signaling appears as the predominant safeguard of the NSC pool under regenerative conditions while Notch signaling is sufficient to maintain NSCs under homeostatic baseline neurogenesis in the uninjured animal.