Fig. 7. Excess Mfn2 modifies mitochondrial morphology. HeLa cells were transfected with expression vectors encoding mtGFP (A, control), mtGFP and Mfn2 (A, +Mfn2) or MF2-IYFFT (B,C). Cells were fixed and decorated with specific antibodies directed against an inner membrane marker (COX2), calnexin or the myc-epitope (myc). Cells were visualized by confocal (A) or conventional microscopy (B,C). The images depict selected cell regions (A) or entire cells (B,C). The insets show enlargements of the areas marked with arrowheads. (A) In control cells, mtGFP and COX2 colocalize in mitochondrial tubules of several µm length and 400-450 nm diameter. In Mfn2 overexpressing cells, mitochondria are spherical (mean diameter, 860±160 nm, n=34) and clustered. In enlarged spherical mitochondria, markers of the inner membrane (COX2) appear to surround the matrix space (mtGFP). (B) At high expression levels, MF2-IYFFT (myc) segregates within the ER (calnexin) and forms membrane networks with modified morphology. (C) MF2-IYFFT expression (myc) does not affect mitochondrial morphology and distribution (mtGFP). Bars, 5 µm (main images) and 1 µm (insets).