Nonrandom gamma-TuNA-dependent spatial pattern of microtubule nucleation at the Golgi

作者：Sanders Anna A W M; Chang Kevin; Zhu Xiaodong; Thoppil Roslin J; Holmes William R^*; Kaverina Irina^*

来源：Molecular Biology of the Cell, 2017, 28(23): 3181-3192.

DOI：10.1091/mbc.E17-06-0425

Noncentrosomal microtubule (MT) nucleation at the Golgi generates MT network asymmetry in motile vertebrate cells. Investigating the Golgi-derived MT (GDMT) distribution, we find that MT asymmetry arises from nonrandom nucleation sites at the Golgi (hotspots). Using computational simulations, we propose two plausible mechanistic models of GDMT nucleation leading to this phenotype. In the "cooperativity" model, formation of a single GDMT promotes further nucleation at the same site. In the "heterogeneous Golgi" model, MT nucleation is dramatically up-regulated at discrete and sparse locations within the Golgi. While MT clustering in hotspots is equally well described by both models, simulating MT length distributions within the cooperativity model fits the data better. Investigating the molecular mechanism underlying hotspot formation, we have found that hotspots are significantly smaller than a Golgi subdomain positive for scaffolding protein AKAP450, which is thought to recruit GDMT nucleation factors. We have further probed potential roles of known GDMT-promoting molecules, including gamma-TuRC-mediated nucleation activator (gamma-TuNA) domain-containing proteins and MT stabilizer CLASPs. While both gamma-TuNA inhibition and lack of CLASPs resulted in drastically decreased GDMT nucleation, computational modeling revealed that only gamma-TuNA inhibition suppressed hotspot formation. We conclude that hotspots require gamma-TuNA activity, which facilitates clustered GDMT nucleation at distinct Golgi sites.

• 出版日期2017-11-7