Thrombospondin-4 controls matrix assembly during development and Repair of Myotendinous Junctions

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Abstract

Tendons are extracellular matrix (ECM)-rich structures that mediate muscle attachments with the skeleton, but surprisingly little is known about molecular mechanisms of attachment. Individual myofibers and tenocytes in Drosophila interact through integrin (Itg) ligands such as Thrombospondin (Tsp), while vertebrate muscles attach to complex ECM fibrils embedded with tenocytes . We show for the first time that a vertebrate thrombospondin, Tsp4b, is essential for muscle attachment and ECM assembly at myotendinous junctions (MTJs). Tsp4b depletion in zebrafish causes muscle detachment upon contraction due to defects in laminin localization and reduced Itg signaling at MTJs. Mutation of its oligomerization domain renders Tsp4b unable to rescue these defects, demonstrating that pentamerization is required for ECM assembly. Furthermore, injected human TSP4 localizes to zebrafish MTJs and rescues muscle detachment and ECM assembly in Tsp4b-deficient embryos. Thus Tsp4 functions as an ECM scaffold at MTJs, with potential therapeutic uses in tendon strengthening and repair.

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Arul Subramanian

University of California, Irvine, Irvine, United States

Competing interests
No competing interests declared.
Thomas F Schilling

University of California, Irvine, Irvine, United States

For correspondence
tschilli@uci.edu

Competing interests
Thomas F Schilling, TFS has filed a provisional patent Thrombospondin proteins and methods of using for treating tendons and ligaments" with US application serial no. 61/835.

Ethics

Animal experimentation: This study was performed in accordance with rules and protocols approved by University of California, Irvine- Institutional Animal Care and Use Committee (UCI-IACUC)(Protocol # 2000-2149-4). Juveniles and adult fish were euthanized with Ethyl 3-aminobenzoate methanesulfonate (Tricaine). Embryos were anesthetized with Tricaine before stimulation assays.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.