Bone morphogenetic protein-2 functions as a negative regulator in the differentiation of myoblasts, but not as an inducer for the formations of cartilage and bone in mouse embryonic tongue

Recombinant BMP-2 inhibited the expressions of markers for the differentiation of skeletal muscle cells, such as myogenin, muscle creatine kinase (MCK), and fast myosin heavy chain (fMyHC), whereas BMP-2 siRNA stimulated such markers. Neither the recombinant BMP-2 nor BMP-2 siRNA altered the expressions of markers for the formation of cartilage and bone, such as osteocalcin, alkaline phosphatase (ALP), collagen II, and collagen X. Further, no formation of cartilage and bone was observed in the recombinant BMP-2-treated tongues based on Alizarin red and Alcian blue stainings. Neither recombinant BMP-2 nor BMP-2 siRNA affected the expression of inhibitor of DNA binding/differentiation 1 (Id1). The ratios of chondrogenic and osteogenic markers relative to glyceraldehyde-3-phosphate dehydrogenase (GAPDH, a house keeping gene) were approximately 1000-fold lower than those of myogenic markers in the cultured tongue.BMP-2 functions as a negative regulator for the final differentiation of tongue myoblasts, but not as an inducer for the formation of cartilage and bone in cultured tongue, probably because the genes related to myogenesis are in an activation mode, while the genes related to chondrogenesis and osteogenesis are in a silencing mode.The development of skeletal muscle proceeds through five phases, as follows [1]: phase 1 (specification), muscle progenitor cells are specified to become muscle cells in somites; phase 2 (migration), the muscle progenitor cells migrate to the presumptive places where muscles are formed; phase 3 (proliferation), the muscle progenitor cells proliferate, increase in number, and become myoblasts; phase 4 (differentiation), the myoblasts fuse to become multinucleated myotubes; phase 5 (maturation), the multinucleated myotubes mature to myofibers, such as fast-twitch myofibers or slow-twitch myofibers.Bone morphogenetic proteins (BMPs) are members of the transforming growth factor β (TGFβ) super family and comprise a highly conserved and exp