Deciphering Cellular Forces during Myoblast Fusion

The fusion of mammalian myoblast cells is an integral part of muscle growth and regeneration. Although the biochemical aspects of cell fusion have been extensively investigated, a quantitative description of the physical phenomena underlying this process has not yet been explored. This study aims to quantify and distinguish both the extracellular and intercellular forces generated by two myoblasts during fusion or the lack thereof. To achieve this goal, we fabricated a protein-patterned polyacrylamide hydrogel with embedded fluorescent particles to employ time-lapse traction force microscopy on isolated pairs of cells. Our results indicate the presence of large intracellular stresses due to the polarizing tangential traction vectors pointing away from the cell-cell interface in both fusing and non-fusing cells. For non-fusing cells, these polarizing stresses were maintained throughout the duration of the time-lapse microscopy as the cells shift to and fro on the protein patterns. However, for cells undergoing fusion, the polarization of the traction vectors ceases as the stresses generated by the cell injecting its nuclei dominates the other. In addition to the tangential forces, we also analyzed the particle displacement field for normal stresses, which are revealed to be negligible under all circumstances. The magnitudes of the normal stresses have been shown to exist at an order of magnitude lower than that of the tangential stresses.