Involvement of Wnt4 signaling during myogenic proliferation and differentiation of skeletal muscle.

The direct effects of Wnt4 on myogenic proliferation and differentiation of skeletal muscle precursors are examined. Wnt4 cDNA was misexpressed in the presumptive limb fields on the right side of stage 16 chick embryos. Muscle development was evaluated at stage 37 with hematoxylin-eosin staining and immunohistochemical staining for fast and slow types of the myosin heavy chain (MyHC). Overexpression of Wnt4 resulted in up-regulation of Pax7 and MyoD1 expression. The muscle mass showed a significant increase compared with that of the control limb. The area for fast MyHC-expressing cells showed a significant increase, whereas a slight decrease was observed for slow MyHC-expressing cells. Wnt4 acted as a stimulator during myogenic proliferation and differentiation, especially, for fast-type muscle in C2C12 cells. The present results are identical to those of myostatin knockout, suggesting that Wnt4 is acting against myostatin as an antagonizing signal for myostatin.