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Recoil after severing reveals stress fiber contraction mechanisms.

ABSTRACT: Stress fibers are cellular contractile actomyosin machines central to wound healing, shear stress response, and other processes. Contraction mechanisms have been difficult to establish because stress fibers in cultured cells typically exert isometric tension and present little kinetic activity. In a recent study, living cell stress fibers were severed with laser nanoscissors and recoiled several mum over approximately 5 s. We developed a quantitative model of stress fibers based on known components and available structural information suggesting periodic sarcomeric organization similar to striated muscle. The model was applied to the severing assay and compared to the observed recoil. We conclude that the sarcomere force-length relation is similar to that of muscle with two distinct regions on the ascending limb and that substantial external drag forces act on the recoiling fiber corresponding to effective cytosolic viscosity approximately 10(4) times that of water. This may originate from both nonspecific and specific interactions. The model predicts highly nonuniform contraction with caps of collapsed sarcomeres growing at the severed ends. A directly measurable signature of external drag is that cap length and recoil distance increase at intermediate times as t(1/2). The severing data is consistent with this prediction.

SUBMITTER: Stachowiak MR

PROVIDER: S-EPMC2711311 | biostudies-literature | 2009 Jul

REPOSITORIES: biostudies-literature

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Recoil after severing reveals stress fiber contraction mechanisms.

Stachowiak Matthew R MR O'Shaughnessy Ben B

Biophysical journal 20090701 2

Stress fibers are cellular contractile actomyosin machines central to wound healing, shear stress response, and other processes. Contraction mechanisms have been difficult to establish because stress fibers in cultured cells typically exert isometric tension and present little kinetic activity. In a recent study, living cell stress fibers were severed with laser nanoscissors and recoiled several mum over approximately 5 s. We developed a quantitative model of stress fibers based on known compone ...[more]

PMID: 19619460

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Project description:BackgroundImproving the yield and fiber quality of upland cotton is a goal of plant breeders. However, increasing the yield and quality of cotton fibers is becoming more urgent. While the growing human population needs more cotton fiber, climate change is reducing the amount of land on which cotton can be planted, or making it difficult to ensure that water and other resources will be available in optimal quantities. The most logical means of improving yield and quality is understanding and manipulating the genes involved. Here, we used comparative transcriptomics to explore differences in gene expression between long- and short-fiber cotton lines to identify candidate genes useful for cotton improvement.ResultsLight and electron microscopy revealed that the initial fiber density was significantly greater in our short-fiber group (SFG) than in our long-fiber group (LFG). Compared with the SFG fibers, the LFG fibers were longer at all developmental stages. Comparison of the LFG and SFG transcriptomes revealed a total of 3538 differentially expressed genes (DEGs). Notably, at all three developmental stages examined, two expression patterns, consistently downregulated (profile 0) and consistently upregulated (profile 7), were identified, and both were significantly enriched in the SFG and LFG. Twenty-two DEGs known to be involved in fiber initiation were detected in profile 0, while 31 DEGs involved in fiber elongation were detected in profile 7. Functional annotation suggested that these DEGs, which included ERF1, TUA2, TUB1, and PER64, affect fiber elongation by participating in the ethylene response, microtubule synthesis, and/or the peroxidase (POD) catalytic pathway. qRT-PCR was used to confirm the RNA sequencing results for select genes.ConclusionsA comparison of SFG and LFG transcription profiles revealed modest but important differences in gene expression between the groups. Notably, our results confirm those of previous studies suggesting that genes involved in ethylene, tubulin, and POD pathways play important roles in fiber development. The 22 consistently downregulated DEGs involved in fiber initiation and the 31 consistently upregulated genes involved in fiber elongation are seemingly good candidate genes for improving fiber initiation and elongation in cotton.

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Recoil after severing reveals stress fiber contraction mechanisms.

Publications

Recoil after severing reveals stress fiber contraction mechanisms.

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