Mutant disturbs normal tooth mineralization and bone formation in zebrafish.

Background: Tricho-dento-osseous (TDO) syndrome is an autosomal dominant disorder characterized by anomalies in hair, teeth and bone (OMIM190320). Various mutations of Distal-Less 3 () gene are found to be responsible for human TDO. The aim of this study was to investigate effects of on tooth and bone development using a zebrafish model.

Methods: The mutant zebrafish lines were established using the gene targeting tool transcription activator-like effector nuclease (TALEN). Micro-computed tomography was used to render the three-dimensional skeletal structures of mutant fishes. The pharyngeal bone along with connected teeth was isolated and stained by Alizarine Red S, then observed under stereomicroscope. Scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) were used to examine the tooth surface morphology and mineral composition. Quantitative real-time PCR was used to analyze gene expression.

Results: A moderate curvature of the spine toward the dorsal side was found at the early larval stages, appearing in 86 out of 100 larvae in group as compared to 3 out of 99 in the group. At the adult stage, three of the thirty homozygotes exhibited prominent abnormal curvature in the spine. SEM revealed morphological surface changes in pharyngeal teeth enameloid, accompanied by a decrease in the mineral content detected by EDS. Furthermore, specific secretory calcium-binding phosphoprotein (SCPP) genes, including , , , , and were significantly downregulated in mutants.

Conclusion: The findings of this study suggest that is critical for enamel mineralization and bone formation in zebrafish. Moreover, the discovery of the downregulation of SCPP genes in mutants sheds new light on the molecular mechanisms underlying TDO syndrome.