Fig. 2. TDP-43 nuclear-cytoplasmic shuttling seen by interspecies heterokaryon assays. Transiently transfected U2OS cells were fused with mouse NIH-3T3 cells upon cycloheximide treatment. Arrows indicate mouse nuclei of the fused cell, distinguished from human nuclei using DAPI staining. (A,B) GFP-tagged as well as FLAG-tagged TDP-43 were analyzed in transfected U2OS or HeLa cells. (C,D) FLAG-tagged hnRNP A1 and hnRNP C1/C2 were used as a controls for protein shuttling. In the case of hnRNP C1/C2, GFP-TDP-43 and FLAG-hnRNP C1/C2 were co-transfected to observe specific TDP-43 shuttling in the same fused cell. Scale bars: 10 µm.