The rapid exchange of MBNL1 and CUGBP1 detected by FRAP (Figs 2, 5 and 6) within SGs and P-bodies, and the ability of SGs to fuse and separate (Fig. 5 and Movies 1-4) as seen in our two models of DM1, are consistent with this hypothesis. This evidence concerns the gene CELF1 and myotonic dystrophy type 1.