Runx2 and Osterix, the transcription factors for osteoblast differentiation, are known as fundamental factors to regulate the development of calcified tissues. However, the biological functions of these factors in the development of the periodontal tissues remain unclear. In this study, we investigated the distribution of Runx2 and Osterix during periodontal tissue development of the mice. Mandibles from 14-day-old mice were prepared for paraffin section. Serial sections of the mandible containing 1 st molar tooth germs were obtained as a thickness of 7 μm. Some sections were stained with hematoxylin and eosin. Others were used for immunohistochemistry for PCNA, Runx2, and Osterix. Epithelial cells in growing end of Hertwig’s epithelial root sheath (HERS) and mesenchymal cells adjacent to the growing end of HERS expressed PCNA. Undifferentiated mesenchymal cells and hard tissue forming cells like cementoblasts and osteoblasts in early stage of differentiation expressed Runx2. Fully differentiated cementoblasts and osteoblasts secreting matrix proteins expressed Osterix. However, the cells terminated the matrix formation did not express Osterix. Periodontal ligament cells expressed Runx2 and Osterix. Pulp cells expressed Runx2 only.These results suggest that Runx2 and Osterix might regulate the differentiation of cementoblasts in the same manner as osteoblasts. Runx2 might participate in the process of cementoblast differentiation in early stage, whether Osterix might regulate the maturation and matrix synthesis of the cells.

Acute lymphoblastic leukemia (ALL), a predominantly pediatric disease involving uncontrolled proliferation of white blood cells within the bone marrow, is strongly associated with chromosomal translocations. The human chromosomal translocation t(12;21)(p12;q22) is the most frequently encountered chromosomal rearrangement in pediatric B-lineage ALL, and results in fusion of the TEL and RUNX1 genes. The resulting TEL/RUNX1 fusion protein is generally thought to be a transcriptional repressor that interferes with RUNX1-mediated transactivation. We used a luciferase assay system to investigate the effects of TEL/RUNX1 and PEBP2β on RUNX1-mediated transactivation. TEL/RUNX1 blocked the synergistic transactivation achieved by PEBP2β and RUNX1, and coimmunoprecipitation and immunofluorescence analyses showed that PEBP2β interacted with TEL/RUNX1 and was sequestered in the cytoplasm. Theses results suggest that TEL/RUNX1 inhibits RUNX1-mediated transactivtion via cytoplasmic sequestration of coactivator(s) such as PEBP2β.