Directionality of developing skeletal muscles is set by mechanical forces
Kazunori Sunadome, Alek Erickson, Delf Kah, Ben Fabry, Csaba Ádori, Polina Kameneva, Louis Faure, Shigeaki Kanatani, Markéta Kaucká, Ivar Dehnisch Ellström, Markéta Tesařová, Tomáš Zikmund, Jozef Kaiser, Steven Edwards, Koichiro Maki, Taiji ADACHI, Takuya Yamamoto, Kaj Fried, Igor Adameyko
Abstract
Formation of oriented myofibrils is a key event in musculoskeletal development. However, the mechanisms that drive myocyte orientation and fusion to control muscle directionality in adults remain enigmatic. Here, we demonstrate that the developing skeleton instructs the directional outgrowth of skeletal muscle and other soft tissues during limb and facial morphogenesis in zebrafish and mouse. Time-lapse live imaging reveals that during early craniofacial development, myoblasts condense into round clusters corresponding to future muscle groups. These clusters undergo oriented stretch and alignment during embryonic growth. Genetic perturbation of cartilage patterning or size disrupts the directionality and number of myofibrils in vivo. Laser ablation of musculoskeletal attachment points reveals tension imposed by cartilage expansion on the forming myofibers. Application of continuous tension using artificial attachment points, or stretchable membrane substrates, is sufficient to drive polarization of myocyte populations in vitro. Overall, this work outlines a biomechanical guidance mechanism that is potentially useful for engineering functional skeletal muscle.