Roles of KMT2D in Enamel Development and Odontogenic Differentiation

Objectives: KMT2D (formerly MLL2/MLL4) has been suggested as a candidate gene of Kabuki syndrome (KS), a syndrome accompanying by craniofacial and odonto-dysplasia. The complex composed of KMT2D and its paralogue KMT2C (formerly MLL3) has been considered to contribute in cell differentiation and embryo development through catalyzing H3K4 mono-methylation (H3K4me1) at enhancers. The objective of this study was to study the mechanism of KMT2D mutation on craniofacial development, particularly on tooth development.
Methods: Frozen slices of fetal mice mandible at 14.5 days, 16.5 days (E14.5, E16.5), and postnatal mice slices at 0, 4^st, 7^stday (PN0, n=3; PN4, PN7,). The slices were stained with immunofluorescence, and observed under laser scanning confocal microscope. The expression patterns of KMT2C, KMT2D and H3K4me1 in the first molar were obtained and analyzed.
Results: By immunofluorescence staining, it was demonstrated that KMT2C, KMT2D and H3K4me1 were strongly expressed in enamel organ (IEE, SR and OEE) but absent in dental mesenchyme, at E14.5 (cap stage) and E16.5 (bell stages). At PN0 (early secretion stage), they were found accumulated in odontoblasts, dental mesenchyme and cervical loops (CL). At PN4 with the initiation of the root formation, KMT2C, KMT2D and H3K4me1were mainly detected in odontoblasts and CL, rarely found in differentiated ameloblasts and other enamel organ tissue. At PN4 (with active proliferative capacity for root elongation), KMT2C, KMT2D and H3K4me1 were mainly found in the CL.
Conclusions: The spatial-temporal expression pattern demonstrated in this study suggested that the roles of KMT2C/KMT2D complex and H3K4me1 in amelogenesis and tooth root development might be in supporting matrix secretion and initial mineralization.