Differentiation dependent expression and distinct subcellular localization of the protooncogene product, PEBP2β/CBFβ, in muscle development

The Pebpb2/Cbfb gene encodes the non-DNA binding subunit of the heterodimeric transcription factor, PEBP2/CBF. To examine the expression of the PEBP2β/CBFβ protein in vivo, we carried out immunohistochemistry using the tissues from adult mice as well as embryos. Although PEBP2β/CBFβ was detected in various tissues to various degrees, interesting features of expression were observed in the skeletal myogenic cells. Here PEBP2β/CBFβ was found mainly to occur as cytoplasmic staining and the intensity of this staining increased depending on the differentiation stage of the cells. In the undifferentiated myoblasts PEBP2β/CBFβ was undetectable, whereas moderate levels of PEBP2β/CBFβ were detected in the elongated and aligned myocytes. PEBP2β/CBFβ appeared to accumulate further when the cells fused to each other to become multinucleated myotubes. Once the muscle fibers were established, PEBP2β/CBFβ was relocated onto or around the Z-lines. PEBP2β/CBFβ was also detected in the cytoplasm of cardiac myocytes and in the smooth muscle cells of the digestive tract. In all the above, the skeletal myotubes were the only case that showed both nuclear and cytoplasmic staining of PEBP2β/CBFβ. Thus, we could show differentiation dependent pattern of PEBP2β/CBFβ expression in muscle development and establish PEBP2β/CBFβ to be a cytoplasmic as well as nuclear protein in vivo.