Possible Roles of Msx2 in Ameloblast differentiation

MSX同源框基因家族在器官发生过程中在多能祖细胞中表达，在细胞分化和增殖中起重要作用。以往的研究表明，MSX2突变小鼠在颅骨骨化和颅骨缝融合方面存在缺陷。本研究应用免疫组织化学和组织学技术，研究了MSX2基因在牙齿发育中的可能作用，并与出生一天的MSX2突变体和野生型小鼠在成釉发生的各个阶段的表型进行了比较。此外，对培养的一天龄小鼠的切牙牙胚进行了组织学分析，野生型和MSX2突变小鼠之间没有明显的表型差异。颈环也没有显示出任何差异。然而，在牙体发育早期，中间层和成釉细胞出现异常。随着细胞分化，成釉细胞与中间层单个细胞之间的异常程度提前变得更加明显。各细胞组分的碱性磷酸酶活性均不足。部分成釉细胞分泌釉质蛋白。在体内培养的中间层和成釉细胞中也发现了类似的异常。成牙本质细胞分化和牙本质形成完整。这些发现表明，MSX2对于成釉器官的发育是必不可少的。

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.