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The isolated comet tail pseudopodium of Listeria monocytogenes: a tail of two actin filament populations, long and axial and short and random.

Sechi AS, Wehland J, Small JV - J. Cell Biol. (1997)

Bottom Line: The exit of a comet tail from bulk cytoplasm into a pseudopodium is associated with a reduction in total F-actin, as judged by phalloidin staining, the shedding of alpha-actinin, and the accumulation of ezrin.We propose that this transition reflects the loss of a major complement of short, random filaments from the comet, and that these filaments are mainly required to maintain the bundled form of the tail when its borders are not restrained by an enveloping pseudopodium membrane.A simple model is put forward to explain the origin of the axial and randomly oriented filaments in the comet tail.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular Biology, Austrian Academy of Sciences, Salzburg. ase@gbf-brauschweig.de

ABSTRACT
Listeria monocytogenes is driven through infected host cytoplasm by a comet tail of actin filaments that serves to project the bacterium out of the cell surface, in pseudopodia, to invade neighboring cells. The characteristics of pseudopodia differ according to the infected cell type. In PtK2 cells, they reach a maximum length of approximately 15 microm and can gyrate actively for several minutes before reentering the same or an adjacent cell. In contrast, the pseudopodia of the macrophage cell line DMBM5 can extend to >100 microm in length, with the bacteria at their tips moving at the same speed as when at the head of comet tails in bulk cytoplasm. We have now isolated the pseudopodia from PtK2 cells and macrophages and determined the organization of actin filaments within them. It is shown that they possess a major component of long actin filaments that are more or less splayed out in the region proximal to the bacterium and form a bundle along the remainder of the tail. This axial component of filaments is traversed by variable numbers of short, randomly arranged filaments whose number decays along the length of the pseudopodium. The tapering of the tail is attributed to a grading in length of the long, axial filaments. The exit of a comet tail from bulk cytoplasm into a pseudopodium is associated with a reduction in total F-actin, as judged by phalloidin staining, the shedding of alpha-actinin, and the accumulation of ezrin. We propose that this transition reflects the loss of a major complement of short, random filaments from the comet, and that these filaments are mainly required to maintain the bundled form of the tail when its borders are not restrained by an enveloping pseudopodium membrane. A simple model is put forward to explain the origin of the axial and randomly oriented filaments in the comet tail.

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Isolated macrophage pseudopodium (a), at higher magnification in b, that shows a prominent axial array of long actin filaments. Bars: (a) 0.5 μm; (b) 0.2 μm.
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Figure 6: Isolated macrophage pseudopodium (a), at higher magnification in b, that shows a prominent axial array of long actin filaments. Bars: (a) 0.5 μm; (b) 0.2 μm.

Mentions: Fig. 5 shows a typical macrophage pseudopodium. The most striking feature is the clear presence of a bundle of axially oriented filaments that splays out into single filaments towards the rear of the bacterium. Short, randomly oriented filaments are also present, but they are far less abundant than in the PtK2 pseudopodium. The tapered end of the tail shows exclusively parallel actin filaments, and there is no indication of multiple discontinuities within the filament bundles, as would be expected for assemblies of short, interconnected filaments. Fractures in the tail bundles, with the appearance of free filament ends, however, were observed in regions of sharp curvature (not shown). We presume that these fractures arose during the sedimentation of the tails onto the support film, or during the pipetting step. An additional example of a macrophage pseudopodium (Fig. 6) clearly shows a parallel array of long actin filaments as the dominating feature of the comet tail.


The isolated comet tail pseudopodium of Listeria monocytogenes: a tail of two actin filament populations, long and axial and short and random.

Sechi AS, Wehland J, Small JV - J. Cell Biol. (1997)

Isolated macrophage pseudopodium (a), at higher magnification in b, that shows a prominent axial array of long actin filaments. Bars: (a) 0.5 μm; (b) 0.2 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139863&req=5

Figure 6: Isolated macrophage pseudopodium (a), at higher magnification in b, that shows a prominent axial array of long actin filaments. Bars: (a) 0.5 μm; (b) 0.2 μm.
Mentions: Fig. 5 shows a typical macrophage pseudopodium. The most striking feature is the clear presence of a bundle of axially oriented filaments that splays out into single filaments towards the rear of the bacterium. Short, randomly oriented filaments are also present, but they are far less abundant than in the PtK2 pseudopodium. The tapered end of the tail shows exclusively parallel actin filaments, and there is no indication of multiple discontinuities within the filament bundles, as would be expected for assemblies of short, interconnected filaments. Fractures in the tail bundles, with the appearance of free filament ends, however, were observed in regions of sharp curvature (not shown). We presume that these fractures arose during the sedimentation of the tails onto the support film, or during the pipetting step. An additional example of a macrophage pseudopodium (Fig. 6) clearly shows a parallel array of long actin filaments as the dominating feature of the comet tail.

Bottom Line: The exit of a comet tail from bulk cytoplasm into a pseudopodium is associated with a reduction in total F-actin, as judged by phalloidin staining, the shedding of alpha-actinin, and the accumulation of ezrin.We propose that this transition reflects the loss of a major complement of short, random filaments from the comet, and that these filaments are mainly required to maintain the bundled form of the tail when its borders are not restrained by an enveloping pseudopodium membrane.A simple model is put forward to explain the origin of the axial and randomly oriented filaments in the comet tail.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular Biology, Austrian Academy of Sciences, Salzburg. ase@gbf-brauschweig.de

ABSTRACT
Listeria monocytogenes is driven through infected host cytoplasm by a comet tail of actin filaments that serves to project the bacterium out of the cell surface, in pseudopodia, to invade neighboring cells. The characteristics of pseudopodia differ according to the infected cell type. In PtK2 cells, they reach a maximum length of approximately 15 microm and can gyrate actively for several minutes before reentering the same or an adjacent cell. In contrast, the pseudopodia of the macrophage cell line DMBM5 can extend to >100 microm in length, with the bacteria at their tips moving at the same speed as when at the head of comet tails in bulk cytoplasm. We have now isolated the pseudopodia from PtK2 cells and macrophages and determined the organization of actin filaments within them. It is shown that they possess a major component of long actin filaments that are more or less splayed out in the region proximal to the bacterium and form a bundle along the remainder of the tail. This axial component of filaments is traversed by variable numbers of short, randomly arranged filaments whose number decays along the length of the pseudopodium. The tapering of the tail is attributed to a grading in length of the long, axial filaments. The exit of a comet tail from bulk cytoplasm into a pseudopodium is associated with a reduction in total F-actin, as judged by phalloidin staining, the shedding of alpha-actinin, and the accumulation of ezrin. We propose that this transition reflects the loss of a major complement of short, random filaments from the comet, and that these filaments are mainly required to maintain the bundled form of the tail when its borders are not restrained by an enveloping pseudopodium membrane. A simple model is put forward to explain the origin of the axial and randomly oriented filaments in the comet tail.

Show MeSH
Related in: MedlinePlus