1/30/2024 0 Comments Multispec 4c 1.1![]() ![]() Mediators bridging the interaction between microtubules and filopodia have not been conclusively identified and the consequence of this interaction on filopodia dynamics is not known. ![]() Microtubules align with actin arcs and filopodia in the peripheral domain of neuronal growth cones ( Schaefer et al., 2002). Consistent with a role of microtubule targeting to focal adhesions in cell motility, nocodazole disrupts tail retraction and slows migration ( Ballestrem et al., 2000). More recently, findings have shown that focal adhesion disassembly after nocodazole washout is dependent on focal adhesion kinase and dynamin ( Ezratty et al., 2005). Microtubule targeting events in the periphery of fibroblasts precede adhesion site remodeling and dissociation ( Kaverina et al., 1999), a process that is dependent on kinesin ( Krylyshkina et al., 2002). Local tensile stress applied to the lamellipodium of B16F1 cells induces formation of adhesion sites and enhances polymerization of microtubules towards the leading edge ( Kaverina et al., 2002a).Īfter reaching the cell periphery, microtubule ends may interact with several target sites involved in coordination of cell movement. In addition, mechanical stress plays a role in adhesion site formation and microtubule entry into areas of actin protrusion. Global disruption of actin filaments enhances microtubule entry into the peripheral domain of growth cones while inhibition of myosin II interferes with filopodia formation and decreases microtubule entry ( Zhou et al., 2002), indicating that actin architecture is a key factor. Microtubules enter the lamellipodium by polymerization at the plus-end ( Kabir et al., 2001) however, at the same time microtubules move rearward closely correlated with actin retrograde movement in the lamellum ( Salmon et al., 2002). Disposition of microtubules in the lamellipodium of a migrating cell is dependent on multiple processes. Microtubule orientation is polarized, the minus-end is pointed toward the centrosome and the plus-end is pointed toward the cell periphery ( Dammermann et al., 2003). In most cells, polymerization of microtubules is nucleated at the centrosome and proceeds toward the cell periphery. We propose that microtubules target filopodia, independent of focal adhesions and plus-end proteins, causing filopodia movement and microtubules regulate filopodia density in lamellipodia wings through filopodia merging events. Correlation of adhesion sites with microtubule targeting to filopodia was not observed and depletion of microtubule plus-end proteins did not significantly alter targeting frequency. The role of adhesion sites and microtubule plus-end proteins in targeting was investigated. Total internal reflection fluorescence microscopy identified microtubules near the ventral surface and upward movement of targeted filopodia. Rapid uncoupling of targeting with nocodazole decreased filopodia merging events and increased filopodia density. Live cell imaging studies show that targeting events in lamellipodia wings temporally correlated with filopodia turning toward the lamellipodium midline and with filopodia merging. We investigated the functional consequence of targeting on filopodia reorganization and examined mechanisms by which microtubules may be guided to, or interact with, filopodia. ![]() In our current studies, analysis of digital fluorescence images revealed targeting of microtubules to filopodia in B16F1 melanoma cells and fibroblasts. Interaction between the microtubule system and actin cytoskeleton has emerged as a fundamental process required for spatial regulation of cell protrusion and retraction activities. ![]()
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