The dominant negative mutation of PAX9 in nonsyndromic tooth agenesis

Paired box 9 (PAX9) is a transcription factor that plays a critical role in the development of human dentition. Although various mutations in the PAX9 gene have been identified to date, the mechanisms by which these mutations cause non-syndromic tooth agenesis (NSTA) remain not fully understood. To study the pathogenesis of NSTA, we investigated a Chinese NSTA family.

Genomic DNA was extracted from the family members. Whole-exome sequencing was performed, followed by Sanger sequencing for validation. The function of the mutant PAX9 was studied using bioinformatics, real-time PCR, Western blotting, luciferase reporter assays, and co-immunoprecipitation.

Here, we assess the functional impact of a novel missense PAX9 variant (c.156 C > G p.C52W), identified in a Chinese family with NSTA, and provide novel insights into the molecular mechanism of PAX9-C52W dysfunction. We show that while PAX9-C52W is expressed and even upregulated, its functionality is severely compromised. The mutation affects the binding affinity between PAX9 and MSX1 and alters the transcriptional activity of BMP4. Mutations such as PAX9-C52W can lead to disturbances in the intricate regulatory networks controlling tooth development. These molecular changes have significant downstream effects, as evidenced by the decreased capacity for osteo/odontogenic differentiation observed in human dental pulp stem cells (hDPSCs) infected with the PAX9-C52W lentivirus.

Overall, our studies reveal a dominant-negative effect of PAX9-C52W on the wild-type PAX9.

Our findings not only provide new insights into the mechanism of NSTA pathogenesis but also expand the current knowledge of how pathogenic variants in PAX9 cause disease.