MUSK and viral infectious disease: It should be noted that the levels of ColQ re-expressed after viral infection of ColQ−/− myotubes may not exactly reflect the endogenous ColQ levels in WT myotubes, which may explain that in ColQ−/− myotubes re-expressing ColQ, the level of agrin-induced MuSK phosphorylation was strongly decreased even before taking into account the increase in the cell surface level of MuSK.