DIFFERENTIATION-DEPENDENT EXPRESSION AND DISTINCT SUBCELLULAR-LOCALIZATION OF THE PROTOONCOGENE PRODUCT, PEBP2-BETA CBF-BETA, IN MUSCLE DEVELOPMENT/

The Pebpb2/Cbfb gene encodes the non-DNA binding subunit of the hetero dimeric transcription factor, PEBP2/CBF. To examine the expression of the PEBP2 beta/CBF beta protein in vivo, we carried out immunohistoche mistry using the tissues from adult mice as well as embryos, Although PEBP2 beta/CBF beta was detected in various tissues to various degrees , interesting features of expression were observed in the skeletal myo genic cells. Here PEBP2 beta/CBF beta was found mainly to occur as cyt oplasmic staining and the intensity of this staining increased dependi ng on the differentiation stage of the cells, In the undifferentiated myoblasts PEBP2 beta/CBF beta was undetectable, whereas moderate level s of PEBP2 beta/CBF beta were detected in the elongated and aligned my ocytes. PEBP2 beta/CBF beta appeared to accumulate further when the ce lls fused to each other to become multinucleated myotubes, Once the mu scle fibers were established, PEBP2 beta/CBF beta was relocated onto o r around the Z-lines. PEBP2 beta/CBF beta was also detected in the cyt oplasm of cardiac myocytes and in the smooth muscle cells of the diges tive tract. In all the above, the skeletal myotubes were the only case that showed both nuclear and cytoplasmic staining of PEBP2 beta/CBF b eta. Thus, we could show differentiation dependent pattern of PEBP2 be ta/CBF beta expression in muscle development and establish PEBP2 beta/ CBF beta to be a cytoplasmic as well as nuclear protein in vivo.