Abstract
Microtubules (MTs) are highly dynamical structures that play a crucial role in cell physiology. In cooperation with microtubule-associated proteins (MAPs), MTs form bundles endowing cells with specific mechanisms to control their shape or generate forces. Whether the dynamics of MTs is affected by the lateral connections that MAPs make between MTs during bundle formation is still under debate. Using in vitro reconstitution of MT bundling, we analyzed the dynamics of MT bundles generated by two plant MAP65 (MAP65-1/4), MAP65-1 being the plant ortholog of vertebrate PRC1 and yeast Ase1. MAP65-1/4 limit the amplitude of MT bundle depolymerization and increase the elongation phases. The subsequent sustained elongation of bundles is governed by the coordination of MT growth, so that MT ends come in close vicinity. We develop a model based on the assumption that both MAP65-1/4 block MT depolymerization. Model simulations reveal that rescue frequencies are higher between parallel than between anti-parallel MTs. In consequence the polarity of bundled MTs by MAP65 controls the amplitude of bundle’s growth. Our results illustrate how MAP-induced MT-bundling, which is finely tuned by MT polarity, robustly coordinates MT elongation within bundles.
Highlights
Microtubules (MTs) are dynamic polar polymers assembled from tubulin heterodimers and alternating polymerization and depolymerization phases at their ends [1]
We set up a biomimetic assay that reproduces the assembly of bundles made of numerous MTs to mimic in vivo MT bundles. We found that both MAP65-1/4 drive bundled MT dynamics into an unlimited growth regime by reducing MT catastrophe and increasing MT rescue events without affecting MT growth and shortening rates
Dynamics of MTs in MAP65-1/4 Induced Bundles The main question we asked in this study is whether dynamics of MTs are modified by lateral MAP65 links between MTs as it occurs in bundles
Summary
Microtubules (MTs) are dynamic polar polymers assembled from tubulin heterodimers and alternating polymerization and depolymerization phases at their ends [1]. MT catastrophes (switch from growth to shrinkage) or rescues (reverse switch from pause or shrinkage to growth) events have received much attention in vivo [2], [3], in vitro [4] and in theoretical studies [5] These sudden transitions of MT dynamics, named dynamic instability, coordinate many aspects of cellular processes crucial to the establishment of cell polarity, cell morphogenesis or cell division. Powering these cellular functions often hinges on the ability of MTs to self-organize into highly ordered structures This is true for most differentiated animal cell types that contain large numbers of MT arrays in non-centrosomal assembly (e.g. neuronal cells, polarized epithelial cells), in most fungi and in acentrosomal plant cells [6]. How the dynamic behavior of the MTs and their polarity within the bundles affect the steady-state of these MT networks and their self-organization into highly ordered arrays remains an important question in cell biology
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