Novel cell-based system to assay cell-cell fusion during myotube formation.

A live assay tool has been established to uncover the precise molecular mechanisms underlying complex cell fusion events in myoblasts. The novel cell-based assay, HiMy (HiBiT-based myoblast fusion), utilizes a recently developed split-luciferase technology. The assay successfully detected cell fusion in differentiating C2C12 myoblast cultures. This allowed us to measure mixing of the cytoplasm, which occurred several hours after the initiation of C2C12 differentiation. Unlike what was reported earlier, the fusion was detected a few hours after the initiation of differentiation. Thus, this assay is sensitive enough to monitor fusion events before they become detectable using conventional methods. Furthermore, a panel of laboratory compounds, including a variety of inhibitors of cellular enzymes or activities, were assayed using the HiMy assay. Lovastatin, a cholesterol biogenesis inhibitor, decreased HiMy activity by approximately 50%. In contrast, mevalonolactone, a precursor for cholesterol synthesis, increased fusion activity. These results confirmed the previous finding that the amount of cellular cholesterol positively correlates with the rate of myoblast fusion during myogenesis. These results indicate that the novel cell fusion assay is a quick, accurate, and robust method to monitor intercellular fusion events.