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Characterization of Drosophila Swiprosin-1, a novel conserved actin cross-linking protein, controlling immune cell migration, wound closure and regulated exocytosis
Filamentous actin (F-actin) is a dynamic polymer providing mechanical forces to change cell morphology. Calcium is a known modulator of actin cytoskeleton organization, required for many cellular functions including cell migration, wound closure and exocytosis. EFHD2/Swiprosin-1 (Swip-1) is an actin...
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| Format: | Doctoral Thesis |
| Language: | English |
| Published: |
Philipps-Universität Marburg
2022
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| Online Access: | PDF Full Text |
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| Summary: | Filamentous actin (F-actin) is a dynamic polymer providing mechanical forces to change cell morphology. Calcium is a known modulator of actin cytoskeleton organization, required for many cellular functions including cell migration, wound closure and exocytosis. EFHD2/Swiprosin-1 (Swip-1) is an actin-binding protein that can link calcium directly to actin network rearrangements.
Upregulation of Swip-1 has been found in a number of pathologies including neurodegenerative diseases and invasive cancer highlighting its importance to study. A role of Swip-1 in cell migration had been previously shown, however, how Swip-1 regulates the underlying F-actin rearrangements, especially in response to calcium, had not been solved, yet.
Drosophila Swip-1 is upregulated in highly motile pupal macrophages and localizes to the protruding lamellipodia. CRISPR/Cas9-mediated swip-1 null mutants are viable, fertile but their macrophages display disrupted lamellipodia formation and defects in integrin-dependent migration. Moreover, Swip-1 is also crucial for the rapid reorganization of F-actin at a wound edge necessary for the healing process to re-establish tissue integrity. Single-cell ablation in the Drosophila larval epidermis showed dramatic reduction of wound closure in swip-1-deficient flies. Rescue experiments unambiguously showed that calcium binding to Swip-1 is essential for lamellipodia formation for both migration and wound closure.
Mechanistically, Swip-1 can cross-link actin networks. Upon calcium ion binding to Swip-1 these crosslinks become transient, relaxing the actin meshwork and allowing severing and branching to take place. At low calcium levels, Swip-1 stabilizes this network. Notably, the calcium-dependent cross-linking activity had previously not been addressed.
A stable yet dynamic network is also required for regulated exocytosis of secretory vesicles in the Drosophila larval salivary gland. Here, Swip-1 is necessary for the efficient cargo expulsion to the lumen. However, the regulatory mechanism seems to be independent of its calcium binding. Rather, changes in phosphorylated non-muscle myosin II might change the contractility of the F-actin coat surrounding the vesicles. This suggests a role of Swip-1 in a signal pathway upstream of the phosphorylation of myosin regulatory light chain. |
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| Physical Description: | 124 Pages |
| DOI: | 10.17192/z2022.0328 |