Possible Roles of Msx2 in Ameloblast differentiation

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Msx homeobox gene family which plays important roles in cell differentiation and proliferation is expressed in multipotent progenitor cells during organogenesis. Previous studies have shown that Msx2 mutant mice had defects in skull ossification and fusion of calvarial sutures. In this study, possible roles of Msx2 gene in odontogenesis were investigated by immunohistochemical and histological techniques, in comparison with phenotypes of one-day-old Msx2 mutant and wild type mice at each stage of amelogenesis. Furthermore, cultured incisor tooth germs of one-day-old mouse were processed for histologic analysis.No obvious phenotypic difference existed between the wild type and Msx2 mutant mice. The cervical loop also showed no discrepancy. However, abnormalities were found in the stratum intermedium and ameloblasts at the early stage of odontogenesis. The degree of abnormalities became more significant between the individual cells of ameloblasts and stratum intermedium in advance with cell differentiation. Each cell component expressed insufficient alkaline phosphatase activity. A part of ameloblasts secreted enamel protein. Similar abnormalities in vivo in the cultured stratum intermedium and ameloblasts were found. The differentiation of odontoblasts and dentin formation were intact. These findings suggest that Msx2 is essential for the development of the enamel organ.