Patterns of tenascin expression during tail regeneration of the amphibian urodele Pleurodeles waltl

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Abstract
We have determined the patterns of expression of tenascin, an extracellular matrix (ECM) glycoprotein, by indirect immunohistofluorescence and immunoblots during the post-traumatic regeneration of the tail distal part of the amphibian urodele Pleurodeles waltl. In normal tails of adult Pleurodeles, tenascin expression is mostly restricted to few connective tissues including the periosteum, the ligaments of vertebral articulation, myotendinous structures, the perimysium and the pia mater; the extracellular matrix is virtually negative. In certain areas of the adult skin the molecule is expressed around cells of the inner epidermal layer, apparently associated with the cell surface. In the first 4-6 days following tail amputation, tenascin expression increases in the stump region in areas surrounding dedifferentiating tendons; the early blastemic epithelium does not express the molecule. The local increase of tenascin in areas where cells dedifferentiate and start to migrate, precedes the increase in fibronectin that occurs later in the mesenchyme of the blastema. From the 8th day of regeneration, there is a sharp increase of the level of expression of the molecule in the extracellular matrix of the loose mesenchyme underlying the epithelium of the blastema which remains negative. The maximal expression in the matrix is reached in 4-to 6-week-old regenerates and then gradually decreased. High levels of tenascin are present in sites of muscle condensation as fibrils oriented parallel to the direction of alignment of myogenic cells and in sites of chondrogenesis particularly in regions of precartilage formation. After the second week of regeneration, tenascin is strongly expressed in the basal lamina of the regenerated skin and, after the fourth week, also at the level of epidermaldermal junctional areas. Like in normal tail ends, in regenerates older than 8 – 9 weeks, tenascin expression is nearly restricted to the muscle connective tissue and myotendinous structures. These results are discussed in view of the possible multiple morphogenetic roles of tenascin in tissue regeneration and repair.