What was tested
Liu, Hao, Zhang, Yue, and Yang at the Stomatological Hospital of Chongqing Medical University used CRISPR/Cas9 to generate a scpp5 knockout zebrafish line and a heat-shock-inducible Tg(hsp70l:scpp5-GFP) line for overexpression studies (Liu et al. 2026, Materials and Methods). scpp5 is a P/Q-rich secretory calcium-binding phosphoprotein expressed specifically in zebrafish tooth germ. The authors also used Tg(dlx2b:Dendra2-NTR) fish to label tooth germ cells and the nitroreductase/metronidazole system to ablate those cells and create an injury-repair model. Larvae were treated with 12 mM metronidazole from 3 to 5 days post-fertilization, and repair was followed from R0D to R7D. All experiments used AB-strain zebrafish, were approved under Ethics Committee permit 2022163, and followed ARRIVE guidelines (Liu et al. 2026, Materials and Methods).
Developmental loss of scpp5 stalls mineralization
The mutant carried a 2-bp deletion at positions 190-191 of the scpp5 coding sequence, producing no detectable functional protein (Liu et al. 2026, Results). Whole-mount in situ hybridization and RT-qPCR showed markedly reduced scpp5 mRNA in tooth tissues. At 9 dpf, approximately 20.59% (21 of 102) of scpp5-/- larvae showed a complete absence of tooth mineralization; even mutants with normal tooth counts had consistently delayed dentin mineralization (Liu et al. 2026, Results, Fig. S1C and Table S3).
In WT fish, the 4V1 enameloid lost alizarin red staining by 4 dpf as the tooth attached functionally to the fifth ceratobranchial. In scpp5-/- fish, functional attachment was delayed until 5 dpf and the enameloid retained alizarin red staining, indicating abnormal mineralization (Liu et al. 2026, Results). Adult mutants had abnormal cusp morphology, rougher tooth surfaces with larger pit-like structures, and significantly reduced calcium and phosphorus by SEM energy-dispersive X-ray spectroscopy (Liu et al. 2026, Results). A 30 mM calcium supplement in the egg water partially rescued dentin mineralization, but a 30 mM phosphorus supplement did not, and neither corrected the enameloid staining defect (Liu et al. 2026, Results).
Wnt/β-catenin mediates the dentin side of the defect
At 4 dpf, scpp5-/- tooth germ showed downregulation of the calcium efflux channel genes atp2b1b, slc24a3, slc24a4a, and slc24a4b, plus reduced expression of the enameloid matrix genes ambn and enam and the dentin matrix genes spp1 and sprac (Liu et al. 2026, Results). Nuclear β-catenin protein was reduced, the Wnt/β-catenin reporter line Tg(7xtcf:nls-mCherry) showed weaker mCherry signal, and the Wnt target genes axin2, c-myc, and lef1 were downregulated (Liu et al. 2026, Results).
Pharmacological activation with 20 µM SKL2001 or genetic activation with heat-shock-induced wnt10a enhanced dentin mineralization in both WT and mutant fish and restored expression of slc24a3, slc24a4a, slc24a4b, spp1, and sprac. However, neither intervention restored atp2b1b, ambn, or enam expression, and the 4V1 enameloid still retained abnormal alizarin red staining at 5 dpf (Liu et al. 2026, Results).
Overexpression accelerates repair but not normal development
During normal development, heat-shock-driven scpp5 overexpression from either 2-5 dpf or 3-6 dpf did not significantly alter tooth mineralization or tooth germ cell development in WT fish (Liu et al. 2026, Results). After MTZ-induced injury, however, overexpression during R0D-R4D accelerated tooth germ cell repair and mineralization. At R1D it upregulated the calcium efflux channel genes atp2b4, slc8a1a, slc8a3, slc24a3, and slc24a4b and the dentin matrix genes spp1 and sprac, without changing ambn or enam (Liu et al. 2026, Results). The Wnt inhibitor Zamaporvint at 100 µM attenuated both the repair acceleration and the upregulation of Wnt/β-catenin signaling and channel genes (Liu et al. 2026, Results).
Why it matters for the whole-tooth engineering route
For the bioengineered tooth germ program, the paper is basic developmental biology, not a clinical protocol. Its value is mechanistic: it places the SCPP5-Wnt/β-catenin axis at the center of both developmental mineralization and injury-induced repair, and it shows that the two processes use overlapping but not identical gene sets. The finding that dentin repair can be boosted while enameloid matrix expression stays unchanged suggests that simply activating Wnt/β-catenin may not be enough to recreate a complete, enameloid-bearing tooth. That distinction matters for anyone trying to engineer a whole tooth from stem cells or organ germs.
What it does not show
The study is in zebrafish, whose pharyngeal teeth and lifelong replacement differ from human dentition. The authors note that scpp5 is non-functional or absent in mammals, so the direct translational path to human tooth regeneration is unclear (Liu et al. 2026, Introduction). There is no human cell source, no large-animal model, no eruption or occlusion data, and no assessment of innervation or immune compatibility. Calcium supplementation and Wnt activation only partially rescued dentin mineralization and did not normalize enameloid, so neither is a ready therapy. The injury model ablates labeled germ cells pharmacologically; it is not a clinically relevant pulp or crown injury.
Where we differ from the coverage
We found no popular or press coverage of this paper. It should not be read as a new tooth-regeneration treatment for humans. It is a zebrafish genetics study that defines a signaling axis and exposes a developmental-versus-repair difference that future engineering strategies will have to account for.
Provenance: grounded in the open-access full text of Liu et al. 2026, Molecules and Cells 49(8):100377 (PMID 42242477, PMCID PMC13312475), DOI 10.1016/j.mocell.2026.100377. Method and sourcing standard at /method/.