The cytoskeletal crosslinking protein MACF1 is dispensable for thrombus formation and hemostasis

Abstract

Coordinated reorganization of cytoskeletal structures is critical for key aspects of platelet physiology. While several studies have addressed the role of microtubules and filamentous actin in platelet production and function, the significance of their crosstalk in these processes has been poorly investigated. The microtubule-actin cross-linking factor 1 (MACF1; synonym: Actin cross-linking factor 7, ACF7) is a member of the spectraplakin family, and one of the few proteins expressed in platelets, which possess actin and microtubule binding domains thereby facilitating actin-microtubule interaction and regulation. We used megakaryocyte- and platelet-specific Macf1 knockout ( Macf1 fl/fl , Pf4-Cre ) mice to study the role of MACF1 in platelet production and function. MACF1 deficient mice displayed comparable platelet counts to control mice. Analysis of the platelet cytoskeletal ultrastructure revealed a normal marginal band and actin network. Platelet spreading on fibrinogen was slightly delayed but platelet activation and clot traction was unaffected. Ex vivo thrombus formation and mouse tail bleeding responses were similar between control and mutant mice. These results suggest that MACF1 is dispensable for thrombopoiesis, platelet activation, thrombus formation and the hemostatic function in mice.

Subtle changes in crosslinking drive diverse anomalous transport characteristics in actin–microtubule networks

“…The cytoskeleton is a complex network of filamentous proteins, including semiflexible actin filaments and rigid microtubules [1][2][3] . Numerous crosslinking proteins that can link actin to actin [4][5][6][7] , microtubules to microtubules [8][9][10] , and actin to microtubules [11][12][13][14][15] enable the cytoskeleton to adopt diverse architectures and stiffnesses to drive key processes such as cell motility, meiosis and apoptosis 10,[16][17][18] . These varying structural and rheological properties, in turn, directly impact the intracellular transport of vesicles and macromolecules traversing the cytoplasm 14,15,19,20 .…”

Actin Crosslinking Family Protein 7 Deficiency Does Not Impair Hearing in Young Mice

“…A recent study investigating the role of ACF7 in platelets using Macf1 fl to conditionally knockout the gene also revealed that ACF7 was not required for proper function in certain contexts. These findings are relevant because, similar to hair cells, platelets have a robust cytoskeletal structure that is required for the cell to survive and function properly ( Schurr et al, 2019 ). This suggests that both hair cells and platelets have possible redundancy of the cytoskeleton proteins to safeguard their precise structure that is essential for their function.…”

Reduced platelet forces underlie impaired hemostasis in mouse models of MYH9 -related disease

“…Heparinized whole blood was diluted in a ratio of 2:1 in Tyrode’s-Hepes buffer containing Ca 2+ ( 43 ). Whole blood or mixed platelet count adjusted blood (5 × 10 5 platelets/μl) was incubated with an anti-GPIX antibody derivate conjugated with DyLight 488 (0.2 μg/ml) at 37°C for 5 min.…”