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C. Elegans Chromosomes Connect to Centrosomes by Anchoring into the Spindle Network

2018; Elsevier BV; Volume: 114; Issue: 3 Linguagem: Inglês

10.1016/j.bpj.2017.11.2112

1542-0086

Stefanie Redemann, Johannes Baumgart, Norbert Lindow, Michael Shelley, Ehssan Nazockdast, Andrea Kratz, Steffen Prohaska, Jan Brugués, Sebastian Fürthauer, Thomas Müller‐Reichert,

Photosynthetic Processes and Mechanisms

The mitotic spindle is a three-dimensional, highly dynamic microtubule based apparatus that ensures the faithful segregation of chromosomes. The dynamics properties are regulated by a number of factors, such as polymerases, depolymerases, motor proteins, cross-linkers and other microtubule-associated proteins. Remarkably, despite the high turnover of microtubules throughout mitosis, the spindle maintains its bipolar structure over longer time periods. We set out to identify the detailed arrangement of microtubules in C. elegans mitotic spindles, and to understand how this arrangement is generated, using a combination of large-scale electron tomography, light microscopy and mathematical modeling. Based on our 3D reconstructions we classified the microtubules composing mitotic spindles in three classes, kinetochore (KMTs), spindle (SMTs) or astral microtubules (AMTs) according to their positions, and quantified distinct properties of each class. While our light microscopy and mutant studies show that microtubules are nucleated from the centrosomes, we find only a few KMTs directly connected to the centrosomes. Indeed, by quantitatively analyzing several models of microtubule growth, we conclude that minus-ends of KMTs have selectively detached and depolymerized from the centrosome. Our results show that the connection between centrosomes and chromosomes is mediated by an anchoring into the entire spindle network and that any direct connections through KMTs are few and likely very transient.