Differential regulation of tropomyosin isoform organization and gene expression in response to altered actin gene expression.

Schevzov, Galina; Lloyd, Catriona; Hailstones, Deborah; Gunning, Peter W.

doi:10.1083/jcb.121.4.811

Cited by 41 publications

(24 citation statements)

References 51 publications

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“…This is entirely consistent with previous studies that have shown that Tm isoforms differ in their ability to restore cell shape to transformed cells (Gimona et al, 1996) and in their impact on neuroepithelial cells (Bryce et al, 2003; Figure 6). In addition, the original demonstration that ␤ and ␥-actin carry different structural information (Schevzov et al, 1992) may be accounted for by their differential impact on Tm isoform levels and organization (Schevzov et al, 1993). In all cases, the alterations in cell shape are consistent with changes in the organization of actin filaments.…”

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confidence: 68%

“…Alterations in the expression of actin and tropomyosin by in vitro transfection studies in different cell types have previously been shown to change the expression of other members of these gene families (Schevzov et al, 1993;Bryce et al, 2003). Consequently, we hypothesized that the observed increase in growth cone size seen in Tm5NM1 neurons could be due to changes in the expression and/or subcellular localization of other cytoskeletal proteins.…”

Section: Recruitment Of Tm5a and Myosin Iib By Tm5nm1 To The Growth Conementioning

confidence: 96%

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Specific Features of Neuronal Size and Shape Are Regulated by Tropomyosin Isoforms

Schevzov

Bryce

Almonte-Baldonado

et al. 2005

MBoC

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Spatially distinct populations of microfilaments, characterized by different tropomyosin (Tm) isoforms, are present within a neuron. To investigate the impact of altered tropomyosin isoform expression on neuronal morphogenesis, embryonic cortical neurons from transgenic mice expressing the isoforms Tm3 and Tm5NM1, under the control of the ␤-actin promoter, were cultured in vitro. Exogenously expressed Tm isoforms sorted to different subcellular compartments with Tm5NM1 enriched in filopodia and growth cones, whereas the Tm3 was more broadly localized. The Tm5NM1 neurons displayed significantly enlarged growth cones accompanied by an increase in the number of dendrites and axonal branching. In contrast, Tm3 neurons displayed inhibition of neurite outgrowth. Recruitment of Tm5a and myosin IIB was observed in the peripheral region of a significant number of Tm5NM1 growth cones. We propose that enrichment of myosin IIB increases filament stability, leading to the enlarged growth cones. Our observations support a role for different tropomyosin isoforms in regulating interactions with myosin and thereby regulating morphology in specific intracellular compartments. INTRODUCTIONThe actin cytoskeleton plays an essential role in the structural changes that initially establish neuronal shape and subsequently contribute to the morphological differentiation of neurons. Actin filaments have been implicated in the initial sprouting of neurites, whereas microtubules strengthen and support the new extensions (Smith, 1988(Smith, , 1994.Tropomyosin (Tm) isoforms, integral components of actin microfilaments, form coiled-coil head-to-tail dimers that bind along the major groove of actin polymers (Phillips et al., 1979). Tms are derived from four highly conserved genes known as the ␣Tm fast , ␤Tm, ␥Tm (Tm5NM), and ␦Tm genes that, via alternative splicing, give rise to Ͼ40 isoforms (LeesMiller and Helfman, 1991;Dufour et al., 1998;Cooley and Bergtrom, 2001). Despite the well understood function of Tms in muscle where, together with the troponin complex, they regulate contraction in a calcium-dependent manner, little is known about their role in nonmuscle cells. In vitro studies have implicated Tms in the stabilization of the actin cytoskeleton by protecting actin filaments from the severing action of gelsolin (Ishikawa et al., 1989) and the depolymerizing action of ADF/cofilin (Bernstein and Bamburg, 1982). Gene transfection studies have demonstrated that tropomyosin isoforms can regulate the organization of actin filaments in transformed cells (Prasad et al., 1993;Boyd et al., 1995;Gimona et al., 1996) and the neuroepithelial cell line B35 (Bryce et al., 2003).In neurons, a strict repertoire of Tm isoforms is known to be expressed. These include TmBr3, Tm5a and Tm5b from the ␣Tm fast gene; multiple products from the ␥Tm gene; and Tm4 from the ␦Tm gene. Most interestingly, Tm isoforms have been previously shown to be spatially and temporally regulated, identifying distinct subcellular compartments. The Tm5a and Tm5b isoforms are enric...

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mentioning

confidence: 68%

Section: Recruitment Of Tm5a and Myosin Iib By Tm5nm1 To The Growth Conementioning

confidence: 96%

Specific Features of Neuronal Size and Shape Are Regulated by Tropomyosin Isoforms

Schevzov

Bryce

Almonte-Baldonado

et al. 2005

MBoC

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“…Furthermore, TGF␤ enhances contractile activity of SCFs without changing SMMHC or NMMHC expression. Further studies are needed to determine whether enhanced ␣-SMA expression influences other structural proteins that are involved in cell contraction in an isoform-specific manner, such as tropomyosin (Schevzov et al, 1993), caldesmon (Bretscher and Lynch, 1985), calponin (Gimona et al, 1992), SM22 (Gimona et al, 1992), and gelsolin (Arora et al, 1999a) or whether it affects regulatory events, including myosin light-chain phosphorylation, small GTPase activation, and calcium signaling (Parizi et al, 2000). The 3ЈUTRs of ␣-cardiac and ␤-cytoplasmic actin have been suggested to facilitate actin isoform sorting in the cytoplasm by localizing to different subcellular compartments (Kislauskis et al, 1993) and the 3ЈUTR of ␣-tropomyosin has been shown to exert functional tumor suppressor activity (Rastinejad et al, 1993).…”

Section: Discussionmentioning

confidence: 99%

Alpha-Smooth Muscle Actin Expression Upregulates Fibroblast Contractile Activity

Hinz

Celetta

Tomasek³

et al. 2001

MBoC

1,114

947

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To evaluate whether ␣-smooth muscle actin (␣-SMA) plays a role in fibroblast contractility, we first compared the contractile activity of rat subcutaneous fibroblasts (SCFs), expressing low levels of ␣-SMA, with that of lung fibroblasts (LFs), expressing high levels of ␣-SMA, with the use of silicone substrates of different stiffness degrees. On medium stiffness substrates the percentage of cells producing wrinkles was similar to that of ␣-SMA-positive cells in each fibroblast population. On high stiffness substrates, wrinkle production was limited to a subpopulation of LFs very positive for ␣-SMA. In a second approach, we measured the isotonic contraction of SCF-and LF-populated attached collagen lattices. SCFs exhibited 41% diameter reduction compared with 63% by LFs. TGF␤1 increased ␣-SMA expression and lattice contraction by SCFs to the levels of LFs; TGF␤-antagonizing agents reduced ␣-SMA expression and lattice contraction by LFs to the level of SCFs. Finally, 3T3 fibroblasts transiently or permanently transfected with ␣-SMA cDNA exhibited a significantly higher lattice contraction compared with wild-type 3T3 fibroblasts or to fibroblasts transfected with ␣-cardiac and ␤-or ␥-cytoplasmic actin. This took place in the absence of any change in smooth muscle or nonmuscle myosin heavy-chain expression. Our results indicate that an increased ␣-SMA expression is sufficient to enhance fibroblast contractile activity. INTRODUCTIONEarly during healing of an open wound, resident dermal fibroblasts proliferate from the wound margin and migrate into the provisional matrix composed of a fibrin clot. About 1 week after wounding, the provisional matrix is replaced by neo-formed connective tissue, known as granulation tissue, essentially composed of small vessels, extracellular matrix, and fibroblastic cells that become activated and modulate into myofibroblasts. The main feature of myofibroblasts is represented by an important contractile apparatus similar to that of smooth muscle (Gabbiani et al., 1971), and in particular by the neo-expression of ␣-smooth muscle actin (␣-SMA), the actin isoform typical of vascular smooth muscle cells (Skalli et al., 1986). Myofibroblasts are recognized to play a central role in closing the wound tissue, through their capacity to produce a strong contractile force (for review see Grinnell, 1994;Rønnov-Jessen et al., 1996;Powell et al., 1999;Serini and Gabbiani, 1999), possibly generated within stress fibers, similar to those present in cultured fibroblasts (Skalli et al., 1986;Serini and Gabbiani, 1999). Because wound contraction takes place when de novo expressed ␣-SMA is incorporated in stress fibers (Darby et al., 1990), it has been suggested that this actin isoform plays an important role in granulation tissue contraction (for review see Serini and Gabbiani, 1999). Although stress fibers have been proposed to function as contractile organelles (Burridge, 1981;Katoh et al., 1998) and their presence has been correlated with the production of isometric tension (Harris et al., 1981), at p...

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“…In zebra fish, a mutation of the TnT2 gene (silent heart, sih) has been found to severely reduce not only TnT expression but also TnI3 and Tm-α (Sehnert et al, 2002), and, in a myoblast cell culture system, a β-actin gene mutation causes reduced protein and mRNA levels of Tm2 and Tm3 (Schevzov et al, 1993). Furthermore, relative mRNA output between contractile gene families in humans has been found at different stages of development, and independently of isoform switching, which suggests the existence of some form of communication between these genes (Wade et al, 1990).…”

Section: Discussionmentioning

confidence: 99%

Troponin I is required for myofibrillogenesis and sarcomere formation inDrosophilaflight muscle

Nongthomba

Clark

Cummins

et al. 2004

Journal of Cell Science

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Myofibrillar proteins assemble to form the highly ordered repetitive contractile structural unit known as a sarcomere. Studies of myogenesis in vertebrate cell culture and embryonic developmental systems have identified some of the processes involved during sarcomere formation. However, isoform changes during vertebrate muscle development and a lack of mutants have made it difficult to determine how these proteins assemble to form sarcomeres. The indirect flight muscles (IFMs) of Drosophila provide a unique genetic system with which to study myofibrillogenesis in vivo. We show in this paper that neither sarcomeric myosin nor actin are required for myoblast fusion or the subsequent morphogenesis of muscle fibres, i.e. fibre morphogenesis does not depend on myofibrillogenesis. However, fibre formation and myofibrillogenesis are very sensitive to the interactions between the sarcomeric proteins. A troponin I (TnI) mutation, hdp3, leads to an absence of TnI in the IFMs and tergal depressor of trochanter (TDT) muscles due to a transcript-splicing defect. Sarcomeres do not form and the muscles degenerate. TnI is part of the thin filament troponin complex which regulates muscle contraction. The effects of the hdp3 mutation are probably caused by unregulated acto-myosin interactions between the thin and thick filaments as they assemble. We have tested this proposal by using a transgenic myosin construct to remove the force-producing myosin heads. The defects in sarcomeric organisation and fibre degeneration in hdp3 IFMs are suppressed, although not completely, indicating the need for inhibition of muscle contraction during muscle development. We show that mRNA and translated protein products of all the major thin filament proteins are reduced in hdp3 muscles and discuss how this and previous studies of thin filament protein mutants indicate a common co-ordinated control mechanism that may be the primary cause of the muscle defects.

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Differential regulation of tropomyosin isoform organization and gene expression in response to altered actin gene expression.

Cited by 41 publications

References 51 publications

Specific Features of Neuronal Size and Shape Are Regulated by Tropomyosin Isoforms

Specific Features of Neuronal Size and Shape Are Regulated by Tropomyosin Isoforms

Alpha-Smooth Muscle Actin Expression Upregulates Fibroblast Contractile Activity

Troponin I is required for myofibrillogenesis and sarcomere formation inDrosophilaflight muscle

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