Molecular cytochemical analysis of correlation,between nuclear distribution of transcription factors and transcriptional activation or cell differentiation inductivity

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Runx2, a transcription factor plays an important role in cell differentiation of pluripotential undifferentiated mesenchyme into osteoblasts and chondrocytes, and regulates transcription of the target genes by binding to the promoter. Molecular cytochemistry was performed to clarify whether nuclear distribution of Runx2 correlates with the transcription activation and/or DNA binding activity of the transcription factors for the differentiation.1. When bone morphology protein-2 was introduced to pre-osteoblasts to promote the differentiation by increasing transcription activation of Runx2 gene, Runx2 was strongly stained in the euchromatin area in nuclei.2. In fetal cartilage of transgenic mice with CoIII-Akt-Tg-GFP, Runx2 appeared in the nuclei of undifferentiated perichondrial cells and proliferating chondrocytes. The staining was increased in the nuclear matrix of mature chondrocytes, and decreased in the differentiated hypertrophy chondrocytes. Nuclear distribution of Runx2 seemed to correlate with DNA binding changes of Runx2 by Akt and chondrocyte differentiation.3. In tibia of new-born mice of Runx2-Tg, Runx2 and β-catenin appeared in the nuclei of undifferentiated perichondrial cells, and Runx2 was distributed in the nuclear matrix of osteoblasts but not in the osteocytes. In fetal mice of Runx2-/-, neither β-catenin nor osterix was stained in the nuclei of undifferentiated perichondrial cells. Nuclear distribution of Runx2 and β-catenin seemed to be related with the differentiation.4. When Runx2/GFP were induced in C3H10T1/2 pluripotent undifferentiated fibroblasts, the cytoplasmic processes of the cells were decreased and became short. Immunostaining of actin was decreased and membranous β-catenin aggregated in the cytoplasm. Nuclear matrix distribution of Runx2 seemed to be related with induction of the cell differentiation.