-Actin is required for cytoskeletal maintenance but not development

Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders/National Institutes of Health, Rockville, MD 20850, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 07/2009; 106(24):9703-8. DOI: 10.1073/pnas.0900221106
Source: PubMed


Beta(cyto)-actin and gamma(cyto)-actin are ubiquitous proteins thought to be essential building blocks of the cytoskeleton in all non-muscle cells. Despite this widely held supposition, we show that gamma(cyto)-actin null mice (Actg1(-/-)) are viable. However, they suffer increased mortality and show progressive hearing loss during adulthood despite compensatory up-regulation of beta(cyto)-actin. The surprising viability and normal hearing of young Actg1(-/-) mice means that beta(cyto)-actin can likely build all essential non-muscle actin-based cytoskeletal structures including mechanosensory stereocilia of hair cells that are necessary for hearing. Although gamma(cyto)-actin-deficient stereocilia form normally, we found that they cannot maintain the integrity of the stereocilia actin core. In the wild-type, gamma(cyto)-actin localizes along the length of stereocilia but re-distributes to sites of F-actin core disruptions resulting from animal exposure to damaging noise. In Actg1(-/-) stereocilia similar disruptions are observed even without noise exposure. We conclude that gamma(cyto)-actin is required for reinforcement and long-term stability of F-actin-based structures but is not an essential building block of the developing cytoskeleton.

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Available from: Edward J Walsh, Oct 16, 2014
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    • "In animal models, Actg KO mice exhibit hearing loss at very early stages of development, which suggest critical and specific functions for g-actin in HCs [Belyantseva et al., 2009]. Perrin and co-workers (2010) demonstrated that Actg1-flox Atoh1-cre mice have nearly normal hearing as young adults, but later develop progressive hearing loss at all frequencies tested. "
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    ABSTRACT: Cytoplasmic actin isoforms beta (β-) and gamma (γ-) perform crucial physiological roles in inner ear hair cells (HC). The stereocilium, which is structured by parallel actin filaments composed of both isoforms, is the responsive organelle to mechanical stimuli such as sound, gravity and head movements. Modifications in isoform proportions affect the function of the stereocilia as previously shown in genetic studies of mutant mice. Here, immunogold labeling TEM studies in mice showed that both β- and γ-actin isoforms colocalize throughout stereocilia actin filaments, adherens junctions and cuticular plates as early as embryonic stage 16.5. Gold-particle quantification indicated that there was 40% more γ- actin than β-actin at E16.5. In contrast, β- and γ-actin were equally concentrated in adult stereocilia of cochlear and vestibular HC. Interestingly, all actin-based structures presented almost five-fold more β-actin than γ-actin in 22 month- old mice, suggesting that γ-actin is probably under-expressed during the aging process. These data provide evidence of dynamic modifications of the actin isoforms in stereocilia, cuticular plates and cell junctions during the whole HC life. This article is protected by copyright. All rights reserved. © 2015 Wiley Periodicals, Inc.
    Full-text · Article · May 2015 · Cytoskeleton
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    • "There are studies describing both actin isoforms’ silencing and overexpression (Peckham et al. 2001; Schevzov et al. 1992; Shmerling et al. 2005; Belyantseva et al. 2009; Bunnell and Ervasti 2010), but they did not give a clear answer to the question of their functional diversification. In cited publications, either only one isoform was knocked down (Belyantseva et al. 2009; Bunnell and Ervasti 2010) or overexpressed (Peckham et al. 2001), or the studies focused on normal cells (Dugina et al. 2009; Schevzov et al. 1992). Because of that we decided to trigger overexpression of the β- or γ-actin isoform in the human colon cancer cell line BE, representing the mesenchymal mode of motility, and to observe its effects on cell migration and invasion capacities. "
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    ABSTRACT: Actins are eukaryotic proteins, which are involved in diverse cellular functions including muscle contraction, cell motility, adhesion and maintenance of cell shape. Cytoplasmic actin isoforms β and γ are ubiquitously expressed and essential for cell functioning. However, their unique contributions are not very well understood. The aim of this study was to determine the effect of β- and γ-actin overexpression on the migration capacity and actin cytoskeleton organization of human colon adenocarcinoma BE cells. In cells overexpressing β- or γ-actin, distinct cytoskeletal actin rearrangements were observed under the laser scanning confocal microscope. Overexpressed actins localized at the submembranous region of the cell body, especially near to the leading edge and on the tips of pseudopodia. The cells transfected with plasmids containing cDNA for β- or γ-actin were characterized by increased migration and invasion capacities. However, the migration velocity was statistically significantly higher only in the case of γ-actin overexpressing cells. In conclusion, the increased level of β- or γ-actin leads to actin cytoskeletal remodeling followed by an increase in migration and invasion capacities of human colon BE cells. These data suggest that expression of both actin isoforms has an impact on cancer cell motility, with the subtle predominance of γ-actin, and may influence invasiveness of human colon cancer.
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    • "Among the upregulated orthologous genes to rat and/or human are those encoding to milk proteins, carbohydrate and lipid metabolism, transcriptional factors [17, 34], transduction of hormones [16], glutathione metabolism [18], and cell differentiation [19, 20]. Others are associated with stromal-epithelial communication [24], cell adhesion [25], lactogenesis [26], and general transcription and translation machinery factors [30] as well as structural [32] and basal metabolic genes [33–35]. "
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