Retinoic Acid Signalling Regulates Zebrafish Tooth Germ Repair Following Injury

Although the role of retinoic acid (RA) signalling in odontogenesis is well established, its involvement in the repair of injured tooth germs remains unclear. To investigate this, we generated a Tg(scpp5:Dendra2-NTR) zebrafish line for labelling tooth germ cells and established a tooth germ injury model using the nitroreductase (NTR)/metronidazole (MTZ) system. We then modulated RA signalling by exogenous activation with RA, retinol, retinal, talarozole (TZ) or Tg(hsp70l:aldh1a2-p2a-mCherry; cryaa:venus), and by suppression with 4-diethylaminobenzaldehyde (DEAB) or Tg(hsp70l:dnRARAA-p2a-DsRed; cryaa:venus), to examine its function in tooth germ repair. Following targeted ablation of tooth germ cells, RA signalling was activated, with aldh1a2 showing the most pronounced upregulation. Exogenous RA promoted injury-induced tooth germ repair, whereas its precursors (retinol and retinal) had no significant effect on aldh1a2 expression or repair. Pharmacological inhibition of RA degradation with TZ enhanced repair, while dominant-negative inhibition of RA signalling impaired it. Furthermore, modulation of aldh1a2 revealed its essential role: inhibition with DEAB attenuated repair, whereas genetic activation facilitated tissue restoration. In summary, this study clarifies the regulatory role of RA signalling in tooth germ injury repair, offering a theoretical foundation and potential therapeutic targets for the treatment of injured tooth germs.