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Microtubules can modulate pseudopod activity from a distance inside macrophages
1Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, USA.
Abstract:
Microtubules are thought to influence cell shape as structural components of an integrated cytoskeletal matrix. Here we show that microtubules can affect the dynamics of macrophage pseudopodia without being integrated into their structure. Macrophages landing on glass surfaces spread within 15 min into flattened circular cells with radial symmetry, and the radial distribution of microtubules reflected this symmetry. Depolymerization of microtubules using nocodazole, colchicine, or vinblastine did not inhibit macrophage spreading or the early establishment of radial symmetry. Shortly after spreading, however, macrophages without microtubules gradually became asymmetric, assuming irregular, lobed profiles. The asymmetry resulted from exaggerated protrusion and retraction of pseudopodia, with net retraction overall. This loss of radial symmetry could be inhibited by treatment of initially spread cells with cytochalasin D, indicating that the change in cell shape was mediated by the actin cytoskeleton. Intact microtubules suppressed the exaggerated pseudopod movements, even when they were separated by a distance from the cell margin. In cells treated with taxol, microtubules remained clustered near the cell center after spreading, yet the dynamics of pseudopodia at the cell margin were reduced and cells maintained a circular profile. Similarly, in cells treated with low concentrations of nocodazole, a much reduced microtubule cytoskeleton nonetheless suppressed pseudopod dynamics. We propose that microtubules act to stabilize cell shape at a distance from the cell edge via a biochemical intermediate that affects the structure or function of the microfilament system.
Insights
Microtubules stabilize macrophage cell shape by regulating pseudopodia dynamics, even when not structurally integrated. This microtubule function is crucial for maintaining cell symmetry and preventing irregular shape changes.
Area of Science:
- Cell Biology
- Cytoskeleton Dynamics
- Macrophage Biology
Background:
- Microtubules are traditionally viewed as structural components of the cytoskeleton.
- Their role in dynamic cellular processes like cell shape regulation is less understood.
Purpose of the Study:
- To investigate the role of microtubules in regulating macrophage pseudopodia dynamics and cell shape.
- To determine if microtubules need to be structurally integrated to influence cell shape.
Main Methods:
- Macrophage cell culture on glass surfaces.
- Depolymerization of microtubules using nocodazole, colchicine, and vinblastine.
- Treatment with cytochalasin D, taxol, and varying concentrations of nocodazole.
- Microscopy to observe cell spreading, symmetry, and pseudopodia dynamics.
Main Results:
- Macrophages initially spread and achieve radial symmetry, with or without intact microtubules.
- Loss of microtubules leads to delayed asymmetry, characterized by irregular pseudopodia protrusion and retraction.
- Intact microtubules, even when not at the cell margin, suppress excessive pseudopodia movement and maintain cell circularity.
- Actin cytoskeleton mediates the shape changes observed upon microtubule depolymerization.
Conclusions:
- Microtubules regulate macrophage cell shape and pseudopodia dynamics independently of direct structural integration.
- Microtubules act at a distance to stabilize cell shape, likely through a biochemical link to the actin cytoskeleton.
- This suggests a novel mechanism for microtubule-mediated cell shape control.