Abstract
BackgroundCell shape changes during cytokinesis and chemotaxis require regulation of the actin cytoskeletal network. Dynacortin, an actin cross-linking protein, localizes to the cell cortex and contributes to cortical resistance, thereby helping to define the cell shape changes of cytokinesis. Dynacortin also becomes highly enriched in cortical protrusions, which are sites of new actin assembly.ResultsWe studied the effect of dynacortin on cell motility during chemotaxis and on actin dynamics in vivo and in vitro. Dynacortin enriches with the actin, particularly at the leading edge of chemotaxing cells. Cells devoid of dynacortin do not become as polarized as wild-type control cells but move with similar velocities as wild-type cells. In particular, they send out multiple pseudopods that radiate at a broader distribution of angles relative to the chemoattractant gradient. Wild-type cells typically only send out one pseudopod at a time that does not diverge much from 0° on average relative to the gradient. Though dynacortin-deficient cells show normal bulk (whole-cell) actin assembly upon chemoattractant stimulation, dynacortin can promote actin assembly in vitro. By fluorescence spectroscopy, co-sedimentation and transmission electron microscopy, dynacortin acts as an actin scaffolder in which it assembles actin monomers into polymers with a stoichiometry of 1 Dyn2:1 actin under salt conditions that disfavor polymer assembly.ConclusionDynacortin contributes to cell polarization during chemotaxis. By cross-linking and possibly stabilizing actin polymers, dynacortin also contributes to cortical viscoelasticity, which may be critical for establishing cell polarity. Though not essential for directional sensing or motility, dynacortin is required to establish cell polarity, the third core feature of chemotaxis.
Highlights
Cell shape changes during cytokinesis and chemotaxis require regulation of the actin cytoskeletal network
This dynamic redistribution of GFP-dynacortin led us to speculate that dynacortin may have a role in chemotaxis
We imaged GFP-dynacortin distribution during the movement of aggregation-competent cells toward cAMP released from a micropipette
Summary
Cell shape changes during cytokinesis and chemotaxis require regulation of the actin cytoskeletal network. Dynacortin, an actin cross-linking protein, localizes to the cell cortex and contributes to cortical resistance, thereby helping to define the cell shape changes of cytokinesis. Dynamic rearrangements of the actin cytoskeleton are required for cell migration, cell polarization, phagocytosis, adhesion, and cytokinesis [1]. This reorganization involves F-actin assembly from soluble monomers in the cytoplasm and their subsequent turnover through depolymerization to replenish the precursor pool [2]. From a variety of genetic, in vivo and in vitro analyses, dynacortin has been found to be an actin cross-linking protein that generates mechanical resistance in the cortex that controls cytokinesis contractility dynamics [8,9,10,11]
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