Abstract
The identification and morphological analysis of mitochondria-ER contacts (MERCs) by fluorescent microscopy is limited by sub-pixel resolution inter-organelle distances. Here, application of a novel Membrane Contact Site (MCS) detection algorithm, MCS-DETECT, to 3D STED super-resolution images reconstructs sub-resolution organelle interactions, identifying diverse MERCs. By EM, elongated ribosome-studded riboMERCs are present in HT-1080 but not COS-7 cells and, correspondingly, MCS-DETECT identifies extended large MERCs selectively in HT-1080. These are morphologically distinct from smaller smooth contacts in COS-7 cells and larger contacts induced in COS-7 cells by expression of an mitochondria-ER linker. Large ribo-MERC expression is reduced in Gp78 knockout HT-1080 cells and their induction by Gp78 in COS-7 cells is dependent on Gp78 ubiquitin ligase activity. Gp78-dependent riboMERCs present complex tubular shapes that intercalate between and contact multiple mitochondria. MCS-DETECT of whole cell super resolution 3D image volumes therefore identifies a novel convoluted tubular morphology for riboMERCs whose formation is dependent on Gp78 ubiquitin ligase activity.
Competing Interest Statement
The authors have declared no competing interest.