Tracing of the developmental origin of the caudal fin muscle in zebrafish

Teleost species possess complex caudal musculoskeletal systems. While mid-trunk muscles exhibit simple segmental patterns, several caudal skeletal muscles display intricate orientations in their muscle fibers. Due to this distinctive morphology, both early and recent researchers have studied the structure and development of the caudal musculoskeletal system. However, the early developmental origin of the cell populations within the caudal muscle system remains largely unknown. In this study, we performed lineage tracing of caudal muscle primordia in zebrafish using a transgenic line expressing EGFP in somite derivatives following tamoxifen induction. This approach allowed us to observe the specific cell populations that contribute to caudal muscle tissue formation at the early larval stage. By monitoring the growth of these labeled cells from the early larval stage, we identified the origins of muscle fibers in caudal fin muscles unique to teleosts, such as the adductor caudalis and flexor caudalis. Our findings provide descriptions that aid in understanding how fish-specialized caudal muscle structures were formed through the modification of developmental processes during evolution.