Abstract
Tissues are shaped and patterned by mechanical and chemical processes. A key mechanical process is the positioning of the mitotic spindle, which determines the size and location of the daughter cells within the tissue. Recent force and position-fluctuation measurements indicate that pushing forces, mediated by the polymerization of astral microtubules against- the cell cortex, maintain the mitotic spindle at the cell center in Caenorhabditis elegans embryos. The magnitude of the centering forces suggests that the physical limit on the accuracy and precision of this centering mechanism is determined by the number of pushing microtubules rather than by thermally driven fluctuations. In cells that divide asymmetrically, anti-centering, pulling forces generated by cortically located dyneins, in conjunction with microtubule depolymerization, oppose the pushing forces to drive spindle displacements away from the center. Thus, a balance of centering pushing forces and anti-centering pulling forces localize the mitotic spindles within dividing C. elegans cells.
Highlights
Patterning tissues by chemical and mechanical processesThe shaping and patterning of living organisms is remarkable in its intricacy yet reproducibility[1]
We focus on mitotic spindle positioning, a key mechanical process that shapes and patterns tissues, and ask what are the molecular mechanisms and physical limits that set the precision by which the spindle is positioned and orientated during mitosis
The most important point made in this review is that pushing forces, generated by microtubule polymerization and using energy derived from the GTPase activity of tubulin, are likely responsible for maintaining the C. elegans mitotic spindle at the cell center during metaphase
Summary
A key mechanical process is the positioning of the mitotic spindle, which determines the size and location of the daughter cells within the tissue. The magnitude of the centering forces suggests that the physical limit on the accuracy and precision of this centering mechanism is determined by the number of pushing microtubules rather than by thermally driven fluctuations. In cells that divide asymmetrically, anti-centering, pulling forces generated by cortically located dyneins, in conjunction with microtubule depolymerization, oppose the pushing forces to drive spindle displacements away from the center. We discussmicrotubule-based mechanisms of the mitotic spindle positioning, a key mechanical process that shapes and patterns tissues. The magnitude of the centering forcesindicates that the physical limiton the accuracy and precision of centering isset by the number of contributing microtubules rather than by thermally driven fluctuations. Keywords Mitosis; spindle; microtubules; precision; cell division; buckling; C. elegans
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