Current Biology
Volume 27, Issue 19, 9 October 2017, Pages 2999-3009.e9
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Nesprin-1α-Dependent Microtubule Nucleation from the Nuclear Envelope via Akap450 Is Necessary for Nuclear Positioning in Muscle Cells

https://doi.org/10.1016/j.cub.2017.08.031Get rights and content
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Highlights

  • BioID of Nesprin-1α identifies centrosomal proteins at myotube nuclear envelope

  • Nesprin-1α-containing LINC complexes recruit Akap450 to myotube nuclear envelope

  • Akap450 is required for microtubule nucleation at the nuclear envelope

  • Microtubule nucleation at the nuclear envelope is involved in nuclear positioning

Summary

The nucleus is the main microtubule-organizing center (MTOC) in muscle cells due to the accumulation of centrosomal proteins and microtubule (MT) nucleation activity at the nuclear envelope (NE) [1, 2, 3, 4]. The relocalization of centrosomal proteins, including Pericentrin, Pcm1, and γ-tubulin, depends on Nesprin-1, an outer nuclear membrane (ONM) protein that connects the nucleus to the cytoskeleton via its N-terminal region [5, 6, 7]. Nesprins are also involved in the recruitment of kinesin to the NE and play a role in nuclear positioning in skeletal muscle cells [8, 9, 10, 11, 12]. However, a function for MT nucleation from the NE in nuclear positioning has not been established. Using the proximity-dependent biotin identification (BioID) method [13, 14], we found several centrosomal proteins, including Akap450, Pcm1, and Pericentrin, whose association with Nesprin-1α is increased in differentiated myotubes. We show that Nesprin-1α recruits Akap450 to the NE independently of kinesin and that Akap450, but not other centrosomal proteins, is required for MT nucleation from the NE. Furthermore, we demonstrate that this mechanism is disrupted in congenital muscular dystrophy patient myotubes carrying a nonsense mutation within the SYNE1 gene (23560 G>T) encoding Nesprin-1 [15, 16]. Finally, using computer simulation and cell culture systems, we provide evidence for a role of MT nucleation from the NE on nuclear spreading in myotubes. Our data thus reveal a novel function for Nesprin-1α/Nesprin-1 in nuclear positioning through recruitment of Akap450-mediated MT nucleation activity to the NE.

Keywords

nuclear envelope
nuclear positioning
centrosome
Nesprin-1
Nesprin-1α
Akap450
skeletal muscle
cytosim computer simulation
microtubules
non-centrosomal MTOC

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8

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