The Primary Cilium: A New Player in Muscle Stem Cell Biology

Adult muscle stem cells are responsible for skeletal muscle regeneration, a process where quiescent muscle stem cells activate, enter the cell cycle, and proliferate to give rise to either lineage-committed myoblasts for new muscle fiber formation, or self-renewing cells to replenish the stem cell reservoir. The regenerative capacity of muscle stem cells relies on their precise reception of environmental cues and appropriate intracellular responses. Quiescent muscle stem cells display a primary cilium, a microtubule-based organelle that protrudes from the cell surface and acts as a hub for chemical and mechanical signal transduction. Recent work has significantly increased our understanding of this organelle, demonstrating that the primary cilium actively regulates signaling pathways that are essential for maintenance of muscle stem cell quiescence, proliferation, and fate decision. In this review, we synthesize the current knowledge and recent advances on how this sensory organelle controls muscle stem cell quiescence, enables mechano-sensation, and regulates activation following tissue injury and during asymmetric self-renewal.