title: Nonmuscle myosin II powered transport of newly formed collagen fibrils at the plasma membrane.
abstract: Collagen fibrils can exceed thousands of microns in length and are therefore the longest, largest, and most size-pleomorphic protein polymers in vertebrates; thus, knowing how cells transport collagen fibrils is essential for a more complete understanding of protein transport and its role in tissue morphogenesis. Here, we identified newly formed collagen fibrils being transported at the surface of embryonic tendon cells in vivo by using serial block face-scanning electron microscopy of the cell-matrix interface. Newly formed fibrils ranged in length from ~1 to ~30 µm. The shortest (1-10 µm) occurred in intracellular fibricarriers; the longest (~30 µm) occurred in plasma membrane fibripositors. Fibrils and fibripositors were reduced in numbers when collagen secretion was blocked. ImmunoEM showed the absence of lysosomal-associated membrane protein 2 on fibricarriers and fibripositors and there was no effect of leupeptin on fibricarrier or fibripositor number and size, suggesting that fibricarriers and fibripositors are not part of a fibril degradation pathway. Blebbistatin decreased fibricarrier number and increased fibripositor length; thus, nonmuscle myosin II (NMII) powers the transport of these compartments. Inhibition of dynamin-dependent endocytosis with dynasore blocked fibricarrier formation and caused accumulation of fibrils in fibripositors. Data from fluid-phase HRP electron tomography showed that fibricarriers could originate at the plasma membrane. We propose that NMII-powered transport of newly formed collagen fibrils at the plasma membrane is fundamental to the development of collagen fibril-rich tissues. A NMII-dependent cell-force model is presented as the basis for the creation and dynamics of fibripositor structures.
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research and Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, United Kingdom.
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Kalson
authors.forename: Tobias
authors.initials: T
authors.lastname: Starborg
authors.forename: Yinhui
authors.initials: Y
authors.lastname: Lu
authors.forename: Aleksandr
authors.initials: A
authors.lastname: Mironov
authors.forename: Sally M
authors.initials: SM
authors.lastname: Humphries
authors.forename: David F
authors.initials: DF
authors.lastname: Holmes
authors.forename: Karl E
authors.initials: KE
authors.lastname: Kadler
mesh_terms: D000205:Actomyosin / Q000378:metabolism; D000600:Amino Acids, Dicarboxylic; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D002642:Chick Embryo; D003094:Collagen / Q000096:biosynthesis / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D005109:Extracellular Matrix / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D016253:Microscopy, Immunoelectron; D024462:Myosin Type II / Q000378:metabolism*; D064800:Prolyl-Hydroxylase Inhibitors / Q000494:pharmacology
chemical_list: D000600:Amino Acids, Dicarboxylic; D064800:Prolyl-Hydroxylase Inhibitors; D003094:Collagen; D000205:Actomyosin; D024462:Myosin Type II; C040947:oxalylglycine
keywords: 3View; SBF-SEM; actin; extracellular matrix; vesicle