Fig. 5. Overexpression of Mfn1 in COS-7 cells caused formation of grape-like clusters with enlarged mitochondria. COS-7 cells transiently transfected with (A,C-E) GFP-Mfn1 or (B) untagged Mfn1 expression constructs. (A) Confocal image of live COS-7 cells. Mitochondria visualized with Mitotracker (red). Transfected cells expressing GFP-Mfn1 (arrows, green). (B) Cells fixed and stained with anti-Mfn1 (green) and counterstained with anti-cytochrome c (red). Transfected cell with typical grape-like perinuclear cluster of mitochondria. (arrow; C-E) High magnification view of cluster-of-grape-like mitochondrial network formed after transient transfection with GFP-Mfn1 (green); mitochondrial intermembrane space labeled with anti-cytochrome c (red). (F) Electron microscope image showing cluster-of-grape-like mitochondrial network in COS-7 cell transiently transfected with GFP-Mfn1 and processed for immunogold-labeling using anti-GFP antibodies. Note the characteristic central space surrounded by tightly packed mitochondria with enlarged mitochondria at the periphery.