Large Maf transcription factor family is a major regulator of fast type IIb myofiber determination
Shunya Sadaki, Ryo Fujita, Takuto Hayashi, Ayano Nakamura, Yui Okamura, Sayaka Fuseya, Michito Hamada, Eiji Warabi, Akihiro Kuno, Akiko Ishii, Masafumi Muratani, Risa Okada, Dai Shiba, Takashi Kudo, Shin’ichi Takeda, Satoru Takahashi
Abstract
Myofibers are broadly characterized as fatigue-resistant slow-twitch (type I) fibers and rapidly fatiguing fast-twitch (type IIa/IIx/IIb) fibers. However, the molecular regulation of myofiber type is not entirely understood; particularly, information on regulators of fast-twitch muscle is scarce. Here, we demonstrate that the large Maf transcription factor family dictates fast type IIb myofiber specification in mice. Remarkably, the ablation of three large Mafs leads to the drastic loss of type IIb myofibers, resulting in enhanced endurance capacity and the reduction of muscle force. Conversely, the overexpression of each large Maf in the type I soleus muscle induces type IIb myofibers. Mechanistically, a large Maf directly binds to the Maf recognition element on the promoter of myosin heavy chain 4, which encodes the type IIb myosin heavy chain, driving its expression. This work identifies the large Maf transcription factor family as a major regulator for fast type IIb muscle determination.