Long continuous actin bundles in Drosophila bristles are constructed by overlapping short filaments.
The actin bundles essential for Drosophila bristle elongation are hundreds of microns long and composed of cross-linked unipolar filaments. These long bundles are built from much shorter modules that graft together. Using both confocal and electron microscopy, we demonstrate that newly synthesized modules are short (1-2 microm in length); modules elongate to approximately 3 microm by growing over the surface of longitudinally adjacent modules to form a graft; the grafted regions are initially secured by the forked protein cross-bridge and later by the fascin cross-bridge; actin bundles are smoothed by filament addition and appear continuous and without swellings; and in the absence of grafting, dramatic alterations in cell shape occur that substitutes cell width expansion for elongation. Thus, bundle morphogenesis has several components: module formation, elongation, grafting, and bundle smoothing. These actin bundles are much like a rope or cable, made by overlapping elements that run a small fraction of the overall length, and stiffened by cross-linking.
Guild
Gregory M
GM
Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA. gguild@sas.upenn.edu
Connelly
Patricia S
PS
Ruggiero
Linda
L
Vranich
Kelly A
KA
Tilney
Lewis G
LG
D008841:Actin Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D019521:Body Patterning / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D004331:Drosophila melanogaster / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D008465:Mechanoreceptors / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D008675:Metamorphosis, Biological / Q000502:physiology; D008840:Microfilament Proteins / Q000172:deficiency / Q000235:genetics; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D011679:Pupa / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure
D002352:Carrier Proteins; D008840:Microfilament Proteins; C020324:fascin