Cellular and molecular dynamics of muscle stem cells during muscle hyperplasia decline in trout – FishMuSC

Skeletal muscle consists mainly of muscle fibers formed during embryonic and fetal development. Except during muscle regeneration following injury, myofiber formation (hyperplasia) ceases around birth in mammals and shortly after hatching in zebrafish. Muscle hyperplasia requires the proliferation and the differentiation of muscle stem cells also called satellite cells (SCs), which are located in a distinct niche, between the basal lamina and the plasma membrane of the myofiber. Once differentiated, these cells either fuse to existing myofibers for generating larger cells (i.e. hypertrophy), or fuse together to form new myofibers (i.e. hyperplasia). Fish of agronomic interest have the extraordinary ability to exhibit a continuous post-larval muscle growth associated with the persistent formation of new myofibres (hyperplasia) that arises from muscle stem cells also called satellite cells. However, the hyperplasic muscle growth declines at the end of the exponential growth phase, and the molecular and cellular mechanisms of muscle hyperplasia arrest are still unexplored. Given that hyperplasia level determines the muscle growth potential, the project objective is to analyse the cellular and molecular dynamic of muscle stem cells during muscle hyperplasia decline in trout. To reach this objective we will study during hyperplasia decline (I) the evolution of the characteristics of satellite cell populations, (ii) the evolution of satellite cell number, (iii) the myogenic capacities of satellite cells. In this project, the use of original biological model (transplantation protocol using mlc2-GFP trout) and innovative technologies allowing in-depth investigation (RNAscope®, 3D imaging and single-cell RNA sequencing) offers a unique opportunity to decipher the cellular and molecular dynamic of muscle stem cells during muscle hyperplasia decline in trout.