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Long continuous actin bundles in Drosophila bristles are constructed by overlapping short filaments.

Guild GM, Connelly PS, Ruggiero L, Vranich KA, Tilney LG - J. Cell Biol. (2003)

Bottom Line: These long bundles are built from much shorter modules that graft together.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA. gguild@sas.upenn.edu

ABSTRACT
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.

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Actin bundles are smooth and continuous after grafting. (a) Confocal image (1-μm optical section) of a macrochaete from a 33-h pupa labeled in vivo with GFP actin showing smooth bundles. (b) Two serial longitudinal sections through an actin bundle from a bristle of a 41-h pupa. Of interest is that these sections, together, illustrate a 9-μm segment (arrowheads) within a single bundle, a region that should contain one or two modules. No evidence can be found of the grafted regions. Bars: (a) 5 μm; (b) 1 μm.
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fig7: Actin bundles are smooth and continuous after grafting. (a) Confocal image (1-μm optical section) of a macrochaete from a 33-h pupa labeled in vivo with GFP actin showing smooth bundles. (b) Two serial longitudinal sections through an actin bundle from a bristle of a 41-h pupa. Of interest is that these sections, together, illustrate a 9-μm segment (arrowheads) within a single bundle, a region that should contain one or two modules. No evidence can be found of the grafted regions. Bars: (a) 5 μm; (b) 1 μm.

Mentions: Using confocal microscopy, we carefully examined individual bundles in bristles that had achieved 50% of their mature length to look for overlapping regions where grafting occurred in unbent bristles. We consistently failed to locate such regions, rather the bundles appeared continuous with no apparent thickenings that one might expect for a graft. An example of this is shown in Fig. 7 a, showing several smooth bundles over a 50-μm length. Ultimately these bundles will reveal approximately sixteen 3-μm modules like those seen in Fig. 1 b as they undergo disassembly.


Long continuous actin bundles in Drosophila bristles are constructed by overlapping short filaments.

Guild GM, Connelly PS, Ruggiero L, Vranich KA, Tilney LG - J. Cell Biol. (2003)

Actin bundles are smooth and continuous after grafting. (a) Confocal image (1-μm optical section) of a macrochaete from a 33-h pupa labeled in vivo with GFP actin showing smooth bundles. (b) Two serial longitudinal sections through an actin bundle from a bristle of a 41-h pupa. Of interest is that these sections, together, illustrate a 9-μm segment (arrowheads) within a single bundle, a region that should contain one or two modules. No evidence can be found of the grafted regions. Bars: (a) 5 μm; (b) 1 μm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2172841&req=5

fig7: Actin bundles are smooth and continuous after grafting. (a) Confocal image (1-μm optical section) of a macrochaete from a 33-h pupa labeled in vivo with GFP actin showing smooth bundles. (b) Two serial longitudinal sections through an actin bundle from a bristle of a 41-h pupa. Of interest is that these sections, together, illustrate a 9-μm segment (arrowheads) within a single bundle, a region that should contain one or two modules. No evidence can be found of the grafted regions. Bars: (a) 5 μm; (b) 1 μm.
Mentions: Using confocal microscopy, we carefully examined individual bundles in bristles that had achieved 50% of their mature length to look for overlapping regions where grafting occurred in unbent bristles. We consistently failed to locate such regions, rather the bundles appeared continuous with no apparent thickenings that one might expect for a graft. An example of this is shown in Fig. 7 a, showing several smooth bundles over a 50-μm length. Ultimately these bundles will reveal approximately sixteen 3-μm modules like those seen in Fig. 1 b as they undergo disassembly.

Bottom Line: These long bundles are built from much shorter modules that graft together.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA. gguild@sas.upenn.edu

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus