Yap-lin28a axis targets let7-Wnt pathway to restore progenitors for initiating regeneration

The sox2 expressing (sox2(+)) progenitors in adult mammalian inner ear lose the capacity to regenerate while progenitors in the zebrafish lateral line are able to proliferate and regenerate damaged HCs throughout lifetime. To mimic the HC damage in mammals, we have established a zebrafish severe injury model to eliminate both progenitors and HCs. The atoh1a expressing (atoh1a(+)) HC precursors were the main population that survived post severe injury, and gained sox2 expression to initiate progenitor regeneration. In response to severe injury, yap was activated to upregulate lin28a transcription. Severe-injury-induced progenitor regeneration was disabled in lin28a or yap mutants. In contrary, overexpression of lin28a initiated the recovery of sox2(+) progenitors. Mechanistically, microRNA let7 acted downstream of lin28a to activate Wnt pathway for promoting regeneration. Our findings that lin28a is necessary and sufficient to regenerate the exhausted sox2(+) progenitors shed light on restoration of progenitors to initiate HC regeneration in mammals.