Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2010 Feb 11;463(7282):823-7.
doi: 10.1038/nature08724.

Mical links semaphorins to F-actin disassembly

Ruei-Jiun Hung  1 , Umar Yazdani, Jimok Yoon, Heng Wu, Taehong Yang, Nidhi Gupta, Zhiyu Huang, Willem J H van Berkel, Jonathan R Terman
Affiliations

Mical links semaphorins to F-actin disassembly

Ruei-Jiun Hung et al. Nature. .

Abstract

How instructive cues present on the cell surface have their precise effects on the actin cytoskeleton is poorly understood. Semaphorins are one of the largest families of these instructive cues and are widely studied for their effects on cell movement, navigation, angiogenesis, immunology and cancer. Semaphorins/collapsins were characterized in part on the basis of their ability to drastically alter actin cytoskeletal dynamics in neuronal processes, but despite considerable progress in the identification of semaphorin receptors and their signalling pathways, the molecules linking them to the precise control of cytoskeletal elements remain unknown. Recently, highly unusual proteins of the Mical family of enzymes have been found to associate with the cytoplasmic portion of plexins, which are large cell-surface semaphorin receptors, and to mediate axon guidance, synaptogenesis, dendritic pruning and other cell morphological changes. Mical enzymes perform reduction-oxidation (redox) enzymatic reactions and also contain domains found in proteins that regulate cell morphology. However, nothing is known of the role of Mical or its redox activity in mediating morphological changes. Here we report that Mical directly links semaphorins and their plexin receptors to the precise control of actin filament (F-actin) dynamics. We found that Mical is both necessary and sufficient for semaphorin-plexin-mediated F-actin reorganization in vivo. Likewise, we purified Mical protein and found that it directly binds F-actin and disassembles both individual and bundled actin filaments. We also found that Mical utilizes its redox activity to alter F-actin dynamics in vivo and in vitro, indicating a previously unknown role for specific redox signalling events in actin cytoskeletal regulation. Mical therefore is a novel F-actin-disassembly factor that provides a molecular conduit through which actin reorganization-a hallmark of cell morphological changes including axon navigation-can be precisely achieved spatiotemporally in response to semaphorins.

PubMed Disclaimer

Figures

Figure 1
Figure 1. Mical regulates actin-rich cellular process morphology
a, Mical protein organization. FAD, flavin adenine dinucleotide; CH, calponin homology. b, Adult Drosophila bristles (arrowheads, drawings) are of varying length, unbranched and slightly curved. c–h, Mical is necessary for normal bristle morphology and is also sufficient to alter morphology when one (×1) or two (×2) copies of different Mical transgenes are expressed specifically within bristles. Mutant, MicalDf(3R)Swp2 (ref. 4). n ≥ 25 animals per genotype; chi-squared test; ***P < 0.0001. i, Bristles resulting from Mical−/− and Mical overexpression are quantitatively distinct and the redox and calponin homology domains of Mical are both required and together are sufficient for Mical-like bristle branching. For wild type, transgene or bristle-specific driver only, there is 0% branching. n ≥ 25 bristles per genotype; data shown, mean ± s.e.m.; scale bars, 25 µm.
Figure 2
Figure 2. Semaphorin, plexin and Mical control F-actin organization and bundling
a, A pupal bristle cell extends a membranous process containing F-actin (green lines, and circles seen in cross-section) bundled together adjacent to the membrane. b, GFPMical (green) localizes to elongating pupal bristle tips (arrows) and adjacent (black arrowheads in a ×3 magnified view, inset) to filopodia-like extensions/branches, which were not seen in wild-type bristles. At older pupal ages, Mical localization forms an actin-like striped pattern (open arrowheads). The white arrowhead shows which region is seen at higher magnification in the inset. GFP, green fluorescent protein. c, d, Images and drawings of F-actin bundles. EM, electron microscopy. Membrane-associated (for example, arrows) and abnormally positioned (for example, arrowheads) bundles are drawn. n > 80 F-actin bundles per genotype; ***P < 0.0001 (compared with wild type); data shown, mean ± s.e.m.
Figure 3
Figure 3. Semaphorin–plexin-mediated actin rearrangements require Mical, which binds and directly regulates actin dynamics
A, Mical (GFPMical) co-localizes (yellow) with plexA at sites of bristle branch formation (arrowhead and inset at a ×2 magnified view) and is activated and required for semaphorin–plexin-dependent branching. PIR, plexin-interacting region; cyto, cytoplasmic portion. n ≥ 28 bristles per genotype; t-test; **P < 0.001, ***P < 0.0001; data shown, mean ± s.e.m. B, Mical co-localizes (yellow) with F-actin during early and late (inset) stages of bristle elongation (a). Purified Mical robustly and selectively associates with F-actin as revealed by dot-blot (b) and actin and microtubule co-sedimentation/pelleting (c, d) assays. Arrowheads, MicalredoxCH; dots, Nus; MT, microtubules; BSA, bovine serum albumin; PHBH, p-hydroxybenzoate hydroxylase; MAPs, microtubule-associated proteins; Sol, G-actin (soluble); Pel, F-actin (pellet). n ≥ 2 per condition; data shown, mean ± s.e.m. C, Pyrene-actin assays, where the fluorescence of polymerized pyrene-actin is higher than monomeric pyrene-actin, reveal that purified MicalredoxCH + NADPH directly alters actin polymerization (a) and induces depolymerization (b), as do high-speed sedimentation/Coomassie staining assays (c; arrow). a.u., arbitrary units.
Figure 4
Figure 4. Mical directly disassembles F-actin and regulates growth cone morphology
A, Negative-staining electron microscopy shows that MicalredoxCH + NADPH significantly decreases F-actin length. n > 120 per treatment; t-test; P < 0.0001. B, Actin (green) filaments bundled with fascin (yellow) are disassembled by MicalredoxCH + NADPH, as seen using pyrene-labelled actin (a), low-speed sedimentation/Coomassie staining (b;arrowhead) and electron microscopy (c). Electron microscopy shows that, similar to untreated controls, F-actin bundles treated with MicalredoxCH (black triangles in graph) are well organized, long and thick with ‘horizontally’ arranged individual actin filaments (arrowheads) and repeating ‘vertical stripes’ of fascin (dots). F-actin bundles treated with MicalredoxCH + NADPH (green squares in graph) are significantly shorter and thinner (n > 21 per treatment; t-test; P < 0.0001) and disassemble into single actin filaments (arrowheads). C, Measuring the area occupied by GFP-actin (red) shows that Mical significantly alters growth cone size. Cb, neuronal cell body. n > 40 growth cones per genotype; t-test; ***P < 0.0001; data shown, mean ± s.e.m.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Tran TS, Kolodkin AL, Bharadwaj R. Semaphorin regulation of cellular morphology. Annu. Rev. Cell Dev. Biol. 2007;23:263–292. - PubMed
    1. Luo Y, Raible D, Raper JA. Collapsin: a protein in brain that induces the collapse and paralysis of neuronal growth cones. Cell. 1993;75:217–227. - PubMed
    1. Zhou Y, Gunput RA, Pasterkamp RJ. Semaphorin signaling: progress made and promises ahead. Trends Biochem. Sci. 2008;33:161–170. - PubMed
    1. Terman JR, Mao T, Pasterkamp RJ, Yu HH, Kolodkin AL. MICALs, a family of conserved flavoprotein oxidoreductases, function in plexin-mediated axonal repulsion. Cell. 2002;109:887–900. - PubMed
    1. Schmidt EF, Shim SO, Strittmatter SM. Release of MICAL autoinhibition by semaphorin-plexin signaling promotes interaction with collapsin response mediator protein. J. Neurosci. 2008;28:2287–2297. - PMC - PubMed

Publication types

MeSH terms