Higuchi Y, Ashwin P, Roger Y, Steinberg G. Early endosome motility spatially organizes polysome distribution.
ACTA ACUST UNITED AC 2014;
204:343-57. [PMID:
24493587 PMCID:
PMC3912533 DOI:
10.1083/jcb.201307164]
[Citation(s) in RCA: 100] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To distribute the protein translation machinery throughout the cytoplasm, polysomes in the fungus Ustilago maydis associate with mobile early endosomes, resulting in long-range motility along microtubules.
Early endosomes (EEs) mediate protein sorting, and their cytoskeleton-dependent motility supports long-distance signaling in neurons. Here, we report an unexpected role of EE motility in distributing the translation machinery in a fungal model system. We visualize ribosomal subunit proteins and show that the large subunits diffused slowly throughout the cytoplasm (Dc,60S = 0.311 µm2/s), whereas entire polysomes underwent long-range motility along microtubules. This movement was mediated by “hitchhiking” on kinesin-3 and dynein-driven EEs, where the polysomes appeared to translate EE-associated mRNA into proteins. Modeling indicates that this motor-driven transport is required for even cellular distribution of newly formed ribosomes. Indeed, impaired EE motility in motor mutants, or their inability to bind EEs in mutants lacking the RNA-binding protein Rrm4, reduced ribosome transport and induced ribosome aggregation near the nucleus. As a consequence, cell growth was severely restricted. Collectively, our results indicate that polysomes associate with moving EEs and that “off- and reloading” distributes the protein translation machinery.
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