Periodontalligament (PDL) fibroblasts have an ectomesenchymal origin and are known to participate not only in formation of PDL but also in the repair and regeneration of the a이acent alveolar bone and cementum. However, little is known about the molecular mechanism which is related to the development and differentiation of PDL cells. Recendy, we reported the PDLs (a periodontalligament-specific) 22 as a PDL fibroblast-specific mRNA which is not expressed in gingival fibroblasts. In this study, to examine the expression and functional characterization of PDμ22 mRNA and prαein in development and differentiation of periodontal 따sue ， we carried out northem analysis, insitu hybridization, immunofluorescence and immunohistochemistry. The expression of PDLs22 mRNA was increased with PDL cell differentiation from the confluent to multilayer stage but decreased slighdy with mineralized nodule formation in vitro. πle PDLs22 protein was localized on the nuclear membrane and expressed throughout the differentiation of PDL fibroblasts in vitro. The PDLs22 mRNA and protein were expressed in the differentiating cementoblasts, PDL fibroblasts and osteoblasts along the r∞t surface and alveolar bone of the developing rat teeth. These results indicate that the PDLs22 plays an irnportant role in the differentiation of cementoblasts and osteoblasts and thus homeostasis of cementum, PDL and alveolar bone.