Fig. 3. GIT1 colocalizes with transferrin receptor (TfR) in endosome-derived structures. COS7 cells transfected for GIT1 and ßPIX. (A-C) Double immunofluorescence on ultrathin cryosections. GIT1 (A) and endogenous TfR (B) colocalize (arrows) within large intracellular structures present in the cytoplasm (C) (GIT1, green; TfR, red; nuclei, blue). (D-G) Immunogold labelling of ultrathin cryosection for GIT1, identified by antibodies to Flag, (FLAG, gold 15 nm), and TfR (gold 10 nm). GIT1 associates with tubulovesicular endosomes (D) and intracellular electron dense structures (E), often displaying bounding membranes (F,G arrows). GIT1 and endogenous TfR associate to the same electron dense structures (E-G), often within small vesicles (G). Bars, (D) 253 nm; (E) 212 nm; (F) 137 nm; (G) 57 nm.