Fig. 6. Mitochondrial nucleoids are mobile and diffuse into 0-mitochondria. Stably transfected 143B-0 cells expressing mtRFP and untransfected 143B-+ cells were co-plated and analyzed without further treatment (A) or 12 hours after PEG-mediated cell fusion (B,C). (A) 143B-0 cells expressing mtRFP have punctate mitochondria that are devoid of mtDNA and of mtTFA. The mitochondria of 143B-+ cells contain mtDNA and mtTFA. (B) Twelve hours after PEG-mediated fusion, the polykaryons derived from the fusion of + and 0 cells depict filamentous mitochondria that contain mtRFP, mtDNA and mtTFA. Nucleoids and mtRFP are distributed throughout the entire mitochondrial compartment. (C) An enlargement of the area boxed in B shows that mtDNA nucleoids are enriched in mtTFA. The position of some mtDNA nucleoids is indicated with arrowheads. Bars, 20 µm.