Comparative Analysis of Gene Expression by cDNA Microarray between Cementoblasts and Periodontal Ligament Cells in the Murine Mandible

The detailed features of cementum and PDL remain unknown and specific markers for cementoblasts and PDL cells have not been identified. Moreover, the molecular mechanism of periodontal tissue development, homeostasis and regeneration is also obscure. Since cementum or PDL tissue in previous studies was usually obtained by manual curettage, it has been difficult to isolate pure cementum or PDL. In the current study, laser capture microdissection (LCM) of undecalcified frozen sections of murine mandible was employed for precise tissue isolation and to obtain intact RNA from cementoblasts and PDL cells of the murine mandible. Over 500 tentative cementoblasts and PDL cells were individually captured using an infrared laser. A bioanalyzer detected peaks of 18S and 28S rRNA, suggesting that the quality of RNA was sufficient. Subsequently, mRNA expression in cementoblasts was compared with that in PDL cells by GeneChip analysis, showing that approximately 2,000 genes were differently expressed between those tissues. Serial cementoblast-positive and PDL-negative genes were subjected to real-time RT-PCR analysis to support GeneChip results, using mandible and femur RNA samples. Several genes were expressed at higher levels in the mandible than in the femur, suggesting that several genes found in this study might be candidates for cementum-specific markers. In this study, a novel experimental system was established to isolate target tissues from undecalcified frozen sections at the cell unit level and to obtain intact RNA. Our methodologies could help to guide further investigation of mineralized tissues and to explore tissue-specific factors.