Ultrastructural localization of microfibrillar fibulin-1 and fibulin-2 during heart development indicates a switch in molecular associations |
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Authors: | N Miosge T Sasaki M-L Chu R Herken R Timpl |
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Institution: | Zentrum Anatomie, Abteilung Histologie, Universit?t G?ttingen, Kreuzbergring 36, D-37075 G?ttingen (Germany), Fax +49 551 397067, e-mail: nmiosge@gwdg.de, DE Max-Planck-Institut für Biochemie, D-82152 Martinsried (Germany), DE Department of Dermatology and Cutaneous Biology, Thomas Jefferson University, Philadelphia (Pennsylvania 1907-5541, USA), US
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Abstract: | The microfibrillar proteins fibulin-1 and fibulin-2 were previously identified as prominent components of the endocardial
cushion tissue (ECT) during heart development and shown to persist in adult valves and septa. Immunogold staining has now
been used to compare their localization in embryonic (days 9–11) and adult mouse heart with that of fibronectin and the chondroitin
sulphate proteoglycan versican. All four proteins were deposited in the ECT, which consists of a hyaluronan-rich, mainly unstructured
matrix, but were barely detectable in myocardial basement membranes or within endocardial cells. Digestion with hyaluronate
lyase selectively released the fibulins and versican but not fibronectin from the ECT. Yet neither of the two fibulins bound
to hyluronan in solid-phase assays, in contrast to versican. In the adult heart valve, all four proteins could be detected
close to cross-striated collagen fibrils or microfibrils, but only versican was lost upon exposure to hyaluronate lyase. The
data indicate that fibulins are associated with the hyaluronan-matrix of ECT through a bridge of versican, but that this association
changes upon valve development to another supramolecular, presumably microfibrillar organization based on fibronectin and/or
fibrillins.
Received 3 April 1998; accepted 8 April 1998 |
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Keywords: | , Heart development, extracellular matrix, heart valves, hyaluronan, immunogold staining, microfibrils, |
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