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Alpha Actin

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Robert J Schwartz – 1st expert on this subject based on the ideXlab platform

  • whole animal knockout of smooth muscle Alpha Actin does not alter excisional wound healing or the fibroblast to myofibroblast transition
    Wound Repair and Regeneration, 2013
    Co-Authors: James J Tomasek, Robert J Schwartz, Carol J Haaksma, Eric W Howard

    Abstract:

    The contractile phenotype and function of myofibroblasts have been proposed to play a critical role in wound closure. It has been hypothesized smooth muscle AlphaActin expressed in myofibroblasts is critical for their formation and function. We have used smooth muscle α-Actin-null mice to test this hypothesis. Full-thickness excisional wounds closed at a similar rate in smooth muscle α-Actin -null and wild type mice. In addition, fibroblasts in smooth muscle α-Actin-null granulation tissue when immunostained with a monoclonal antibody that recognizes all muscle Actin isoforms exhibited a myofibroblast-like distribution and a stress fiber-like pattern, demonstrating that these cells acquired the myofibroblast phenotype. Dermal fibroblasts from smooth muscle α-Actin-null and wild type mice formed stress fibers and supermature focal adhesions, and generated similar amounts of contractile force in response to transforming growth factor-β1. Smooth muscle γ-Actin and skeletal muscle AlphaActin were expressed in smooth muscle α-Actin-null myofibroblasts, as demonstrated by immunostaining, real-time PCR, and mass spectrometry. These results demonstrate that smooth muscle α-Actin is not necessary for myofibroblast formation and function and for wound closure, and that smooth muscle γ-Actin and skeletal muscle α-Actin may be able to functionally compensate for the lack of smooth muscle α-Actin in myofibroblasts.

  • myoepithelial cell contraction and milk ejection are impaired in mammary glands of mice lacking smooth muscle Alpha Actin
    Biology of Reproduction, 2011
    Co-Authors: Carol J Haaksma, Robert J Schwartz, James J Tomasek

    Abstract:

    Mammary myoepithelial cells are specialized smooth musclelike epithelial cells that express the smooth muscle Actin isoform: smooth muscle AlphaActin (ACTA2). These cells contract in response to oxytocin to generate the contractile force required for milk ejection during lactation. It is believed that ACTA2 contributes to myoepithelial contractile force generation; however, this hypothesis has not been directly tested. To evaluate the contribution of ACTA2 to mammary myoepithelial cell contraction, Acta2 null mice were utilized and milk ejection and myoepithelial cell contractile force generation were evaluated. Pups suckling on Acta2 null dams had a significant reduction in weight gain starting immediately postbirth. Cross-fostering demonstrated the lactation defect is with the Acta2 null dams. Carmine alum whole mounts and conventional histology revealed no underlying structural defects in Acta2 null mammary glands that could account for the lactation defect. In addition, myoepithelial cell formation and organization appeared normal in Acta2 null lactating mammary glands as evaluated using an Acta2 promoter-GFP transgene or phalloidin staining to visualize myoepithelial cells. However, mammary myoepithelial cell contraction in response to oxytocin was significantly reduced in isolated Acta2 null lactating mammary glands and in in vivo studies using Acta2 null lactating dams. These results demonstrate that lack of ACTA2 expression impairs mammary myoepithelial cell contraction and milk ejection and suggests that ACTA2 expression in mammary myoepithelial cells has the functional consequence of enhancing contractile force generation required for milk ejection.

  • recruitment of the tinman homolog nkx 2 5 by serum response factor activates cardiac Alpha Actin gene transcription
    Molecular and Cellular Biology, 1996
    Co-Authors: Chingyi Chen, Robert J Schwartz

    Abstract:

    We recently showed that the cardiogenic homeodomain factor Nkx-2.5 served as a positive Acting accessory factor for serum response factor (SRF) and that together they provided strong transcriptional activation of the cardiac AlphaActin promoter, depending upon intact serum response elements (SREs) (C. Y. Chen, J. Croissant, M. Majesky, S. Topouz, T. McQuinn, M. J. Frankovsky, and R. J. Schwartz, Dev. Genet. 19:119-130, 1996). As shown here, Nkx-2.5 and SRF collaborated to activate the endogenous murine cardiac AlphaActin gene in 10T1/2 fibroblasts by a mechanism in which SRF recruited Nkx-2.5 to the AlphaActin promoter. Activation of a truncated promoter consisting of the proximal AlphaActin SRE1 occurred even when Nkx-2.5 DNA-binding activity was blocked by a point mutation in the third helix of its homeodomain. Investigation of protein-protein interactions showed that Nkx-2.5 was bound to SRF in the absence of DNA in soluble protein complexes retrieved from cardiac myocyte nuclei but could also be detected in coassociated binding complexes on the proximal SRE1. Recruitment of Nkx-2.5 to an SRE depended upon SRF DNA-binding activity and was blocked by the dominant negative SRFpm1 mutant, which allowed for dimerization of SRF monomers but prevented DNA binding. Interactive regions shared by Nkx-2.5 and SRF were mapped to N-terminal/helix I and helix II/helix III regions of the Nkx-2.5 homeodomain and to the N-terminal extension of the MADS box. Our study suggests that physical association between Nkx-2.5 and SRF is one way that cardiac specified genes are activated in cardiac cell lineages.

James A Carson – 2nd expert on this subject based on the ideXlab platform

  • SRF and TEF-1 control of chicken skeletal AlphaActin gene during slow-muscle hypertrophy.
    The American journal of physiology, 1996
    Co-Authors: James A Carson, R J Schwartz, F W Booth

    Abstract:

    The purpose of this study was to delineate the AlphaActin regulatory elements and transcription factors that are responsible for conferring stretch-overload responsiveness during hypertrophy of the anterior latissimus dorsi (ALD) muscle of young chickens by weighting one wing. Minimal promoter constructs were evaluated by direct injection into the ALD, which demonstrated that both serum response element 1 (SRE1) and the transcriptional enhancer factor 1 (TEF-1) elements were sufficient for increased expression during stretch overload. A mutated SRE1 prevented expression in both basal and stretched ALD muscles, whereas a mutated TEF-1 element reduced Actin promoter function in both control and stretched muscles. The serum response factor (SRF)-SRE1 binding complex demonstrated faster migration in mobility shift assays from day 3-and day 6-stretched ALD nuclear extracts relative to their control. TEF-1 binding was qualitatively increased in stretched extracts at day 3 but not day 6 of stretch overload. Skeletal AlphaActin mRNA accumulated from day 3 to day 6 of stretch overload. These data demonstrate that SRE1 is necessary and sufficient for stretch-overload responsiveness from the skeletal AlphaActin promoter and that the SRF-SRE1 binding complex migrates faster in stretched nuclear extracts of hypertrophied relative to control extracts from intact ALD muscles of chickens.

  • srf and tef 1 control of chicken skeletal Alpha Actin gene during slow muscle hypertrophy
    American Journal of Physiology-cell Physiology, 1996
    Co-Authors: James A Carson, R J Schwartz, Frank W Booth

    Abstract:

    The purpose of this study was to delineate the AlphaActin regulatory elements and transcription factors that are responsible for conferring stretch-overload responsiveness during hypertrophy of th…

  • regulation of skeletal Alpha Actin promoter in young chickens during hypertrophy caused by stretch overload
    American Journal of Physiology-cell Physiology, 1995
    Co-Authors: James A Carson, Robert J Schwartz, Frank W Booth, M E Coleman, Craig S Stump

    Abstract:

    Anterior latissimus dorsi (ALD) muscles of 3-wk-old male chickens were injected with plasmids containing various lengths of the chicken skeletal AlphaActin promoter (ranging from -2,090 to -77 rel…

Frank W Booth – 3rd expert on this subject based on the ideXlab platform

  • srf and tef 1 control of chicken skeletal Alpha Actin gene during slow muscle hypertrophy
    American Journal of Physiology-cell Physiology, 1996
    Co-Authors: James A Carson, R J Schwartz, Frank W Booth

    Abstract:

    The purpose of this study was to delineate the AlphaActin regulatory elements and transcription factors that are responsible for conferring stretch-overload responsiveness during hypertrophy of th…

  • regulation of skeletal Alpha Actin promoter in young chickens during hypertrophy caused by stretch overload
    American Journal of Physiology-cell Physiology, 1995
    Co-Authors: James A Carson, Robert J Schwartz, Frank W Booth, M E Coleman, Craig S Stump

    Abstract:

    Anterior latissimus dorsi (ALD) muscles of 3-wk-old male chickens were injected with plasmids containing various lengths of the chicken skeletal AlphaActin promoter (ranging from -2,090 to -77 rel…