title: Force measurements on cargoes in living cells reveal collective dynamics of microtubule motors.
abstract: Many cellular cargoes move bidirectionally along microtubules, driven by teams of plus- and minus-end-directed motor proteins. To probe the forces exerted on cargoes during intracellular transport, we examined latex beads phagocytosed into living mammalian macrophages. These latex bead compartments (LBCs) are encased in membrane and transported along the cytoskeleton by a complement of endogenous kinesin-1, kinesin-2, and dynein motors. The size and refractive index of LBCs makes them well-suited for manipulation with an optical trap. We developed methods that provide in situ calibration of the optical trap in the complex cellular environment, taking into account any variations among cargoes and local viscoelastic properties of the cytoplasm. We found that centrally and peripherally directed forces exerted on LBCs are of similar magnitude, with maximum forces of ~20 pN. During force events greater than 10 pN, we often observe 8-nm steps in both directions, indicating that the stepping of multiple motors is correlated. These observations suggest bidirectional transport of LBCs is driven by opposing teams of stably bound motors that operate near force balance.
authors.affiliation: Pennsylvania Muscle Institute and Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Adam G
authors.initials: AG
authors.lastname: Hendricks
authors.forename: Erika L F
authors.initials: EL
authors.lastname: Holzbaur
authors.forename: Yale E
authors.initials: YE
authors.lastname: Goldman
mesh_terms: D000818:Animals; D001692:Biological Transport; D001696:Biomechanical Phenomena / Q000502:physiology; D002138:Calibration; D002451:Cell Compartmentation; D002460:Cell Line; D002465:Cell Movement; D002470:Cell Survival; D060833:Cellular Microenvironment; D004398:Dyneins / Q000378:metabolism; D004548:Elasticity; D016547:Kinesins / Q000378:metabolism; D007840:Latex; D051379:Mice; D008863:Microspheres; D008870:Microtubules / Q000378:metabolism*; D020409:Molecular Motor Proteins / Q000378:metabolism*; D052898:Optical Tweezers; D010587:Phagocytosis; D010588:Phagosomes / Q000378:metabolism; D011485:Protein Binding; D014783:Viscosity
chemical_list: D007840:Latex; D020409:Molecular Motor Proteins; D004398:Dyneins; D016547:Kinesins