Oral Presentation 24th Australian Conference on Microscopy and Microanalysis 2016

Analysis of ER-mitochondria contacts by correlative fluorescence microscopy and soft X-ray tomography of mammalian cells  (#4)

Kirstin Elgass 1 , Elizabeth Smith 2 , Mark LeGros 2 , Carolyn Larabell 2 , Mike Ryan 1
  1. Monash University, Melbourne, Clayton, VIC, Australia
  2. National Centre for X-ray Tomography, Advanced Light Source, Berkeley, USA

Mitochondrial fission is important for organelle transport, mitochondrial and cellular function and plays a key role in apoptosis. Changes to the fission process can manifest itself in a wide variety of neurological diseases. In mammals mitochondrial fission is primarily executed by the largely cytosolic GTPase dynamin-related protein 1 (Drp1) that oligomerizes around mitochondria and thus constricts the organelle. The mitochondrial dynamics proteins MiD49 and MiD51 have been reported to be involved in mitochondrial fission by recruiting the master fission mediator Drp1 from the cytosol to the mitochondrial outer membrane [1]. In an independent study ER tubules have been shown to wrap around and constrict mitochondria prior to a fission event [2].

Here we present correlative cryogenic fluorescence microscopy and soft x-ray tomography [3] to link MiD49/51 and ER involvement in mitochondrial fission and to characterize the 3D structure of ER-mitochondria contact sites at MiD49/51 foci with high resolution. We also used confocal live cell imaging to investigate the spatial and temporal relationship between MiD proteins and ER tubules in general and during fission events in particular to gain further insight into this complex process. Using this emerging approach we were able to show that MiD49/51 ER contact sites play a key role in mitochondrial constriction as well as mitochondrial fission. 

  1. C. S. Palmer, L. D. Osellame, D. Laine, O. S. Koutsopoulos, A. E. Frazier, M. T. Ryan, “MiD49 and MiD51, new components of the mitochondrial fission machinery”, EMBO Reports 12, 565-573 (2011).
  2. J. R. Friedman, L. L. Lackner, M. West, J. R. DiBenedetto, J. Nunnari, G. K. Voeltz, “ER tubules mark sites of mitochondrial division”, Science 334, 358-362 (2011).
  3. E. A. Smith, B. P. Cinquin, M. Do, G. McDermott, M. A. Le Gros, C. A. Larabell, “Correlative cryogenic tomography of cells using light and soft x-rays”, Ultramicroscopy 143, 33-40 (2014).