Identification and functional analysis of two novel PAX9 mutations

Area of Science:

• Genetics
• Developmental Biology
• Oral Biology

Background:

• The paired-domain transcription factor PAX9 is crucial for tooth development.
• Heterozygous mutations in PAX9 are associated with human tooth agenesis.
• Nonsyndromic tooth agenesis presents with varying degrees of missing teeth.

Purpose of the Study:

• Identify and characterize novel mutations in PAX9 associated with nonsyndromic tooth agenesis in Chinese patients.
• Investigate the functional impact of these mutations on PAX9 protein activity, specifically DNA binding and transcriptional activation.
• Correlate mutation severity with clinical phenotypes of tooth agenesis.

Main Methods:

• Genetic sequencing to identify mutations in PAX9.
• Immunofluorescence and immunoblotting to assess protein localization.
• Gel shift and super shift assays to evaluate DNA-binding affinity.
• Reporter gene assays to measure transcriptional activation.

Main Results:

• Two novel missense mutations, gly6arg (G6R) and ser43lys (S43K), were identified in the PAX9 paired domain.
• Mutations did not affect nuclear localization but reduced DNA binding affinity.
• G6R exhibited higher DNA binding affinity and transcriptional activation than S43K.
• Clinical phenotypes ranged from missing teeth to peg-shaped incisors, correlating with mutation severity.

Conclusions:

• The identified PAX9 mutations contribute to nonsyndromic tooth agenesis.
• Impaired DNA binding of mutant PAX9 proteins is a key mechanism underlying tooth development defects.
• The degree of DNA-binding deficiency correlates with the clinical severity of tooth agenesis.