Fig. 8. The ultrastructure of clustered mitochondria is modified and their enveloping double membranes are closely apposed. Hela cells were transfected with an empty vector (A) or with a vector encoding Mfn2 (B,C) and processed for electron microscopy. (A) In control cells, sections depict tubular mitochondria of 250-350 nm diameter.

(B) Mitochondrial distribution and morphology is modified in Mfn2- transfected cells. Mitochondria are clustered, and their diameters can surpass 1 µm (upper left region). In enlarged mitochondria, cristae membranes are swollen and/or difficult to identify. (C) The double membranes of clustered mitochondria are in direct contact (arrowheads), but do not merge. Arrows in B and C point to electron dense material that is absent from control cells, and accumulates between mitochondria. Bars, 500 nm (A,B); 200 nm (C).