Browsing by Author "Larraín, J"

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    Antisense inhibition of decorin expression in myoblasts decreases cell responsiveness to transforming growth factor β and accelerates skeletal muscle differentiation
    (2001) Riquelme, C; Larraín, J; Schönherr, E; Henriquez, JP; Kresse, H; Brandan, E
    Decorin is a member of the family of the small leucine-rich proteoglycans. In addition to its function as an extracellular matrix organizer, it has the ability to activate the epidermal growth factor receptor, and it forms complexes with various isoforms of transforming growth factor beta (TGF-beta), Decorin is expressed during skeletal muscle differentiation and is up-regulated in dystrophic muscle. In this study we investigated the role of decorin in TGF-beta -dependent inhibition of myogenesis, To probe the function of decorin during myogenesis, C2C12 myoblasts were stably transfected with a plasmid expressing antisense decorin mRNA. The re; suiting inhibition of decorin expression led to the expression of myogenin, a master transcription factor for muscle differentiation, under growth conditions and accelerated skeletal muscle differentiation as determined by the expression of creatine kinase, In contrast myogenin expression was inhibited by adenovirally induced decorin expression or by adding exogenous decorin, Reduced synthesis of decorin resulted in a 7-fold decreased sensitivity to TGF-beta -mediated inhibition of myogenin expression. In contrast, adenovirally induced decorin expression in wild type cells resulted in a 5-fold increased sensitivity to TGF-beta -mediated inhibition of myogenin expression. Transfection studies with the TGF-beta -dependent promoter of the plasminogen activator inhibitor-1 coupled with luciferase revealed that the transducing receptors for TGF-beta1 and TGF-beta2 were involved in the different responses of wild type and anti-sense decorin myoblasts, These results demonstrate that a reduction of decorin expression or of decorin availability results in a decreased responsiveness to TGF-beta. These findings strongly suggest a new role for decorin during skeletal muscle terminal differentiation by activating TGF-beta -dependent signaling pathways.
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    Syndecan-4 regulates non-canonical Wnt signalling and is essential for convergent and extension movements in Xenopus embryos
    (2006) Muñoz, R; Moreno, M; Oliva, C; Orbenes, C; Larraín, J
    Early shaping of Xenopus laevis embryos occurs through convergent and extension movements, a process that is driven by intercalation of polarized dorsal mesodermal cells and regulated by non-canonical Wnt signalling(1-3). Here, we have identified Xenopus syndecan-4 (xSyn4), a cell-surface transmembrane heparan sulphate proteoglycan. At the gastrula stage, xSyn4 is expressed in the involuting dorsal mesoderm and the anterior neuroectoderm. Later, it is found in the pronephros, branchial arches, brain and tailbud. Both gain- and loss-of-function of xSyn4 impaired convergent extension movements in Xenopus embryos and in activin-treated ectodermal explants. xSyn4 interacts functionally and biochemically with the Wnt receptor Frizzled7 (xFz7) and its signal transducer Dishevelled (xDsh). Furthermore, xSyn4 is necessary and sufficient for translocation of xDsh to the plasma membrane - a landmark in the activation of non-canonical Wnt signalling(1-3). Our results suggest that the ability of xSyn4 to translocate xDsh is regulated by fibronectin, a component of the extracellular matrix required for proper convergent extension movements(4-6). We propose a model where xSyn4 and fibronectin cooperate with xFz7 and Wnt in the specific activation of the non-canonical Wnt pathway.