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. Author manuscript; available in PMC: 2018 Nov 13.
Published in final edited form as: ACS Biomater Sci Eng. 2017 Feb 9;3(11):2727–2732. doi: 10.1021/acsbiomaterials.6b00802

Figure 1. Model for mitochondrial Spire1C and ER-anchored INF2 mediated mitochondrial constriction via actin filament assembly.

Figure 1

(Reproduced (and/or Modified) with permission from Manor et al.15, Copyright 2016 eLife Sciences Publications, Ltd.) (A) Spire1C:actin complexes on mitochondria associate with INF2 on the ER. Actin filaments nucleated by Spire1C are elongated by the actin polymerization activity of INF2. The actin filament elongation activity exerts pressure on the mitochondrial outer membrane, thereby driving constriction of the latter. Tethering complexes may play a role in maintaining association between ER and mitochondrial membranes. Myosin-II dimers and the related contractile actin ring, which may also be involved in mitochondrial constriction, are not shown for simplicity. (B) Computational results showing mitochondrial shapes resulting from deformation by constricting pressure P developed by the actin polymerization and/or actin contractile based mechanisms. The mitochondrial constriction site was modeled as a tubular membrane of about 680 nm length and with initial radius R = 230 nm. The dark blue strip in the middle represents the 50 nm wide zone of the pressure application. The images correspond to 3 ° of the mitochondria constriction characterized by cross-sectional radii r in the narrowest place of 145 nm, 110 nm and 65 nm. The corresponding values of the pressure P, the required numbers of the polymerizing actin filaments, Nf, and the required tensions in the actin contractile ring, Ym, are presented in the main text. (C) The cross-sectional radius in the narrowest place of the mitochondria shape, r, as a function of the pressure, P, exerted on the limited region in the middle of the constriction region. The radius, r, and the pressure, P, are presented in the universal dimensionless forms, r/R, and PR3/2κ, where R is the initial (preceding the deformation) mitochondrial radius and κ is the membrane bending modulus. The dashed lines indicate the specific deformations presented in Figure 1. (D) The number of the actin filaments, Nf, and the tension in the actin contractile ring, γm, providing the pressure as functions of the resulting mitochondria deformation. The deformation is quantified by r/R.