Possible Roles of Msx2 in Ameloblast differentiation

在器官发生过程中，在细胞分化和增殖中起重要作用的Msx同源盒基因家族在多能祖细胞中表达。先前的研究表明，Msx2突变小鼠在颅骨骨化和颅骨缝合线融合方面存在缺陷。本研究通过免疫组织化学和组织学技术，比较1日龄Msx2突变型和野生型小鼠在成牙发育各阶段的表型，探讨Msx2基因在成牙发育中的可能作用。并对培养1日龄小鼠门牙胚进行组织学分析。野生型与Msx2突变小鼠表型无明显差异。宫颈袢也无差异。然而，在牙形成的早期，中间层和成釉细胞出现了异常。随着细胞的分化，成釉细胞的单个细胞与中间层之间的异常程度越来越明显。各细胞组分碱性磷酸酶活性表达不足。部分成釉细胞分泌珐琅质蛋白。在体内培养层、中间细胞和成釉细胞中也发现了类似的异常。成牙髓细胞分化和牙本质形成完整。这些发现表明Msx2对牙釉质器官的发育至关重要。

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.