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. 2012 Jun 19;22(12):1057-65.
doi: 10.1016/j.cub.2012.03.066. Epub 2012 May 31.

Genetically separable functions of the MEC-17 tubulin acetyltransferase affect microtubule organization

Irini Topalidou  1 , Charles Keller, Nereo Kalebic, Ken C Q Nguyen, Hannah Somhegyi, Kristin A Politi, Paul Heppenstall, David H Hall, Martin Chalfie
Affiliations

Genetically separable functions of the MEC-17 tubulin acetyltransferase affect microtubule organization

Irini Topalidou et al. Curr Biol. .

Abstract

Background: Microtubules (MTs) are formed from the lateral association of 11-16 protofilament chains of tubulin dimers, with most cells containing 13-protofilament (13-p) MTs. How these different MTs are formed is unknown, although the number of protofilaments may depend on the nature of the α- and β-tubulins.

Results: Here we show that the enzymatic activity of the Caenorhabiditis elegans α-tubulin acetyltransferase (α-TAT) MEC-17 allows the production of 15-p MTs in the touch receptor neurons (TRNs) MTs. Without MEC-17, MTs with between 11 and 15 protofilaments are seen. Loss of this enzymatic activity also changes the number and organization of the TRN MTs and affects TRN axonal morphology. In contrast, enzymatically inactive MEC-17 is sufficient for touch sensitivity and proper process outgrowth without correcting the MT defects. Thus, in addition to demonstrating that MEC-17 is required for MT structure and organization, our results suggest that the large number of 15-p MTs, normally found in the TRNs, is not essential for mechanosensation.

Conclusion: These experiments reveal a specific role for α-TAT in the formation of MTs and in the production of higher order MTs arrays. In addition, our results indicate that the α-TAT protein has functions that require acetyltransferase activity (such as the determination of protofilament number) and others that do not (presence of internal MT structures).

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Figures

Figure 1
Figure 1. Mutant phenotype and expression of mec-17 and atat-2
(A) Touch sensitivity is largely reduced in mec-17 mutant animals and slightly decreased in atat-2 mutants (mean ± S.E.M.; n = 30). (B) PLM neurons in wild-type larvae have more mec-17 mRNA (mean number of molecules ± S.E.M.; n = 10) than atat-2, mec-7, or mec-3 mRNA. Black bars indicate the number of mRNAs in the cell body and white bars the number of process mRNAs. See also Figure S1.
Figure 2
Figure 2. Loss of mec-17 alters TRN morphology
(A) The ALM anterior process of a young mec-17(ok2109) adult has many swellings (using mec-17Δ::gfp); a similar process in wild type does not. Scale bars = 20 μm. (B) ALM and PLM processes are longer in a young mec-17(ok2109) adult than in a similarly aged wild type (both express mec-17Δ::gfp). The positions of the cell bodies are indicated by arrows. Scale bars = 100 μm. See also Figure S2 and Figure S3.
Figure 3
Figure 3. Effects of mec-17 and atat-2 loss on MT and protofilament number
(A) Electron micrographs of ALM neurons. Scale bars = 100 nm. Arrows indicate MTs with luminal material. HPF fixations, no tannic acid. (B) MTs have variable numbers of protofilaments in tannic acid-stained mec-17(ok2109) and mec-17(ok2109);atat-2(ok2415) animals. The asterisk indicates a 15-p MT having larger diameter then the wild-type 15-p MTs. Note the MT hook in the mec-17(ok2109) cell. Scale bars = 100nm. HPF + tannic acid fixations, except wild-type panel which was fixed in glut + tannic acid. See also Figure S3.
Figure 4
Figure 4. Electron tomograms of ALM processes
(A, B) An IMOD model of a wild type ALM process is shown from oblique and lateral aspects, respectively, to emphasize the regularity of microtubules (blue) within the TRN process. Cargoes lie next to the bundle (ribosomes, red; large vesicle, yellow), and the microtubule bundle deforms locally to admit passage of the vesicle, as does the ALM plasma membrane (gold). Scale bars throughout = 100 nm. (C) Two orthoslices through the same wild type ALM tomogram compare transverse views where the process contains a ribosome (arrow) and the large vesicle (double asterisk). Other views of the wild-type ALM tomogram (panels a-c) have been shown for demonstration purposes on the movie gallery of WormAtlas (http://www.wormatlas.org/movies/pln1_720x480HQ.mov) and in [43], a review of EM methods). (D, E) Two views of an IMOD model of a large swelling of the mutant ALM process. Three distinct groups of MTs are seen. First, many MTs (blue), which are found outside the swelling do not pass through it, possibly due to tubule breakage. Second, two other MTs (red) traverse the swelling along independent paths before rejoining the main (blue) bundle on either side. Third, a large bundle of MTs (green) bend dramatically to follow the outer border of the swelling before returning to rejoin the blue bundle on either side. Panel A shows the swelling from a lateral aspect. ALM plasma membrane (shown in gold) is closely bound to the limits of the microtubule bundle, as if the membrane has ballooned out to cover the bundle. Panel B is a transverse view of the ALM process (compare to similar views in panel E for a wild type process).
Figure 5
Figure 5
A TRN axonal swelling seen in an L3 stage mec-17 mutant animal changes as the animal move. Shown are 4 images from Video S1. Elimination of the swelling is observed as the axon stretches. Asterisk indicates the position of the swellings. Scale bars = 5 μm and 1um (zoomed image). See also Video S1.
Figure 6
Figure 6. Enzymatically inactive MEC-17 rescues touch sensitivity and process extension in the TRNs
(A) Similar rescue of touch insensitivity occurs with mec-17(+) and mutated genes that produce proteins that cannot acetylate MTs (mec-17dW and mec-17D144N). (n = 20; p < 0.001 in all cases). (B) Enzymatically inactive forms of MEC-17 prevent the production of the posterior ALM process but not process swelling. Scale bars = 20 μm. See also Figure S4.
Figure 7
Figure 7. Enzymatically inactive MEC-17 does not rescue the MT and protofilament defects
(A) Electron micrographs of ALM neurons in mec-17 and mec-17-atat-2 mutant animals expressing the enzymatically inactive mec-17(dW). Scale bars throughout = 100 nm. Left panel had HPF using 1.5% tannic acid + 0.5% glut; right panel used HPF in osmium/acetone (no tannic acid). (B) Tannic acid stained mec-17;mec-17(dW), and mec-17;atat-2;mec-17(dW) mutant MTs containing 13-p, 14-p and 15-p protofilaments. HPF using 0.25% tannic acid + 0.5% glut.
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References

    1. Tilney LG, Bryan J, Bush DJ, Fujiwara K, Mooseker MS, Murphy DB, Snyder DH. Microtubules: evidence for 13 protofilaments. J Cell Biol. 1973;59:267–275. - PMC - PubMed
    1. Burton PR, Hinkley RE. Further electron miscroscopic characterization of axoplasmic microtubules of the ventral cord of the crayfish. J Submicrosc Cytol. 1974;6:311–326.
    1. Burton PR, Hinkley RE, Pierson GB. Tannic acid-stained microtubules with 12, 13, and 15 protofilaments. J Cell Biol. 1975;65:227–233. - PMC - PubMed
    1. Afzelius BA, Bellon PL, Lanzavecchia S. Microtubules and their protofilaments in the flagellum of an insect spermatozoon. J Cell Sci. 1990;95(Pt 2):207–217. - PubMed
    1. Hirose K, Amos WB, Lockhart A, Cross RA, Amos LA. Three-dimensional cryoelectron microscopy of 16-protofilament microtubules: structure, polarity, and interaction with motor proteins. J Struct Biol. 1997;118:140–148. - PubMed

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