Axin2 Deficiency Causes Hypomineralization and Delayed Tooth Development

Axin2 negatively regulates the Wnt signaling pathway, which plays a crucial role in multiple tooth development phases. This study aimed to investigate the effects of Axin2 deficiency on tooth development in zebrafish, which are categorized as polyphyodonts. To investigate the role of Axin2 in tooth formation, we generated Axin2 knockout zebrafish using the CRISPR/Cas9 system. Tooth development in zebrafish was observed in the transgenic line, which specifically emits fluorescence in dental tissues. Micro-computed tomography and field emission scanning electron microscopy were used to evaluate tooth shape. Tooth elemental composition was examined using energy-dispersive spectrometry analysis, and gene expression was determined using quantitative polymerase chain reaction. The results showed that the body length of the Axin2 mutant was significantly lower than that of the wild type. β-Catenin expression increased in the dental pulp of the Axin2 mutant compared with that of Axin2^+/+ zebrafish. Confocal imaging showed that initiation and morphogenesis of teeth were sequentially delayed at positions 2V and 1V. Dentin elements, including phosphorus, calcium, carbon, and oxygen, were detected at significantly low levels in Axin2^-/- zebrafish. In addition, runx2a, runx2b, sp7, scpp5, and col1a1a/b expression was significantly reduced in Axin2^-/-. The results show that the loss of Axin2 function causes hypomineralization and delayed tooth development in zebrafish and suggest that spatiotemporal regulation of Wnt signaling is necessary for the normal maturation of odontoblasts.