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Actin pushes in bizarre places.

Powell K - J. Cell Biol. (2005)

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Affiliation: kendallpowell@comcast.net

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Then something else attracts my attention and I move on—it's a lack of commitment on my part. ” So it's no surprise that one of Tilney's major contributions—proposing actin polymerization as a method of force generation within the cell—came through two landmark papers characterizing unorthodox systems: the acrosomal reaction in both starfish and sea cucumber sperm, and the cell-to-cell motility of the Listeria monocytogenes bacterium... Since 80% of the actin was a monomer before the reaction and appeared amorphous in the images, Tilney reasoned that the only way to generate the process so quickly would be actin polymerization. “It was pretty obvious it had to be assembled, but I got a lot of heat for this,” he says. “The key question was, how can you push and polymerize at the same time?” The same puzzle would come up again, 16 years later when Tilney teamed up with Daniel Portnoy... It moved with the comet to the cell surface and into a cell extension that is eventually engulfed by a neighboring cell (Tilney and Portnoy, 1989)... Tilney wrote, “thus, this insidious beast has managed to multiply and spread cell-to-cell without leaving the cytoplasm of its host. ” (Portnoy had objected to the original wording, which included a description of the beast's “Machiavellian deviousness. ”) The work led others to discover actin nucleation proteins such as the bacterial ActA protein (Domann et al., 1992; Kocks et al., 1992) and the Arp2/3 complex (Welch et al., 1997)... The system could be reconstituted in vitro (Theriot et al., 1994; Loisel et al., 1999), and without myosin, so it clinched the idea that polymerization was generating the motility of the bugs... The force-by-elongation mystery would eventually be answered by a mathematical demonstration that Brownian motion could account for actin elongation pushing a membrane forward (Mogilner and Oster, 1996)... Matt Welch, who purified the actin nucleation complex, says the 1989 Listeria paper, “was really the culmination of this whole field of actin polymerization as a mode of motility... You didn't need myosin to move these bacteria around and people made extremely good use of that system to show that what Tilney was saying in the 1973 [acrosomal process] paper was really true. ” Mark Mooseker, a coauthor on that first acrosome paper, says Tilney, still using a 45-yr-old Philips 200 scope, remains one of the best electron microscopists in the field. “He is an absolute hero of mine and his impact is just huge. ” Most recently, says Tilney, his studies have “drifted again” to look at a parasitic nematode: “a very curious beast with a sophisticated external gut—it's both entertaining and disgusting. ” We would expect no less.

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Actin drives the acrosomal reaction (left to right).TILNEY
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uro2: Actin drives the acrosomal reaction (left to right).TILNEY


Actin pushes in bizarre places.

Powell K - J. Cell Biol. (2005)

Actin drives the acrosomal reaction (left to right).TILNEY
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2254856&req=5

uro2: Actin drives the acrosomal reaction (left to right).TILNEY

View Article: PubMed Central - PubMed

Affiliation: kendallpowell@comcast.net

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

Then something else attracts my attention and I move on—it's a lack of commitment on my part. ” So it's no surprise that one of Tilney's major contributions—proposing actin polymerization as a method of force generation within the cell—came through two landmark papers characterizing unorthodox systems: the acrosomal reaction in both starfish and sea cucumber sperm, and the cell-to-cell motility of the Listeria monocytogenes bacterium... Since 80% of the actin was a monomer before the reaction and appeared amorphous in the images, Tilney reasoned that the only way to generate the process so quickly would be actin polymerization. “It was pretty obvious it had to be assembled, but I got a lot of heat for this,” he says. “The key question was, how can you push and polymerize at the same time?” The same puzzle would come up again, 16 years later when Tilney teamed up with Daniel Portnoy... It moved with the comet to the cell surface and into a cell extension that is eventually engulfed by a neighboring cell (Tilney and Portnoy, 1989)... Tilney wrote, “thus, this insidious beast has managed to multiply and spread cell-to-cell without leaving the cytoplasm of its host. ” (Portnoy had objected to the original wording, which included a description of the beast's “Machiavellian deviousness. ”) The work led others to discover actin nucleation proteins such as the bacterial ActA protein (Domann et al., 1992; Kocks et al., 1992) and the Arp2/3 complex (Welch et al., 1997)... The system could be reconstituted in vitro (Theriot et al., 1994; Loisel et al., 1999), and without myosin, so it clinched the idea that polymerization was generating the motility of the bugs... The force-by-elongation mystery would eventually be answered by a mathematical demonstration that Brownian motion could account for actin elongation pushing a membrane forward (Mogilner and Oster, 1996)... Matt Welch, who purified the actin nucleation complex, says the 1989 Listeria paper, “was really the culmination of this whole field of actin polymerization as a mode of motility... You didn't need myosin to move these bacteria around and people made extremely good use of that system to show that what Tilney was saying in the 1973 [acrosomal process] paper was really true. ” Mark Mooseker, a coauthor on that first acrosome paper, says Tilney, still using a 45-yr-old Philips 200 scope, remains one of the best electron microscopists in the field. “He is an absolute hero of mine and his impact is just huge. ” Most recently, says Tilney, his studies have “drifted again” to look at a parasitic nematode: “a very curious beast with a sophisticated external gut—it's both entertaining and disgusting. ” We would expect no less.

Show MeSH