Histone Methyltransferase Mll4 Drives Transcriptional Activation and Cell Differentiation in Tooth Development
Objectives: MLL4, also known as KMT2D, is an epigenetic regulator essential for proper organogenesis and cell differentiation and the major cause for Kabuki syndrome, a human developmental disorder. The objective of this study is to characterize the tooth defect phenotype in a dental epithelium-specific Kabuki syndrome mouse model and identify the developmental and molecular mechanisms underlying Mll4’s regulation of tooth development. Methods: We generated a conditional knockout mouse line that has tissue-specific deletion of the Mll4 gene in the dental epithelium (Krt14-Cre;Mll4fl/fl, or Mll4-cKO). Tissues were harvested at both postnatal (2 and 8 weeks) and embryonic (embryonic day 14.5–19.5, or birth) stages and were examined using micro-computed tomography (CT), histological, and gene expression analyses. Three biological replicates were examined for each experimental group; Student’s t test was used for statistical analysis. Results: Micro-CT analysis revealed 100% penetrance of enamel dysplasia in adult Mll4-cKO mice. Additionally, neonatal Mll4-cKO mice exhibited abnormal molar cusp shape and delayed ameloblast differentiation, which likely contribute to enamel dysplasia. RNA-seq analysis indicated that approximately 34% (31) of 92 known amelogenesis-related genes were significantly downregulated in Mll4-cKO teeth. CUT&RUN-seq analysis suggested that about 26% (8) of the 31 genes are direct targets of Mll4. To further identify the mechanism, additional bioinformatics analysis is in progress. Conclusions: Collectively, our findings demonstrate that Mll4 regulates amelogenesis by activating the expression of key genes involved in ameloblast differentiation.