Madin-Darby canine kidney (MDCK) cells showing the distribution of the tight-junction protein ZO-3 and mitochondria. ZO-3 was detected with a rabbit anti–ZO-3 antibody prelabeled with the Zenon® Alexa Fluor® 488 Rabbit IgG Labeling Kit (Cat. no. Z25302). Endogenous biotin in the mitochondria was labeled using streptavidin (Cat. no. S888) followed by a rabbit anti-streptavidin antibody prelabeled with the Zenon® Alexa Fluor® 555 Rabbit IgG Labeling Kit (Cat. no. Z25305). The nuclei were stained with DAPI (Cat. no. D1306, D3571, D21490).