【Background】
Skeletal muscles are composed of slow-twitch fiber and fast-twitch fiber. Transcriptional factor Tead induces muscle differentiation with its cofactor Taz. However, whether Tead controls slow- and fast-twitch fiber is unknown. Thus, we focused on Vgll3, another cofactor of Tead, and investigated its role in muscle differentiation. 
【Result】
We established Vgll3 expressing C2C12 cells and differentiated these cells. Vgll3 expressing cells showed upregulation of muscle differentiation markers and an increase in slow-twitch fiber marker Myh7 with a decrease in fast-twitch fiber marker Myh4. These results suggest that Vgll3 increases slow-twitch fiber.
Recent studies reported Taz activation induces Vgll3 expression. Thus, we used the Lats1/2 inhibitor, which induces Taz activation. Lats1/2 inhibitor induces Vgll3 expression and upregulation of Myh7 and Myh4. This result suggests that Lats1/2 inhibition induces Taz activation to increase fast-twitch fiber and Vgll3 expression to increase slow-twitch fiber simultaneously.
【Conclusion】
Our results suggested that Vgll3 increases slow-twitch fiber, and Lats1/2 inhibition increase slow- and fast-twitch fiber via activation of Vgll3 and Taz. Aging significantly decreases fast-twitch fiber and causes older adults injury. Thus, Tead and its cofactors are important for aging treatment.