The formation of myotendinous junctions (MTJs) is a fundamental component of a functional musculoskeletal system. Muscles interact with tendons at their attachment sites, causing a reorganization of the extracellular matrix (ECM) into connective tissue structures that can bear the large forces exerted by muscle contraction. The transcription factors Scleraxis (Scx) and Mohawk (Mkx), as well as the membrane glycoprotein Tenomodulin (Tnmd), specify early tendon progenitors and regulate ECM production, and we recently discovered an ECM protein and Integrin (Itg) ligand called Thrombospondin-4b (Tsp4b) in zebrafish that is regulated by Scx and required for muscle attachment. How tendon progenitors reach sites of muscle attachment and influence ECM assembly and muscle adhesion at the MTJ remains unclear. The current proposal addresses these issues using the advantages of the zebrafish for in vivo imaging and genetic manipulation. The long-term goal of the proposed research is to understand the spatial dynamics of ECM assembly and cell fate specification in tendons and ligaments. Two primary hypotheses guide the research: 1) Mkx and Tnmd interact with Scx to control tenocyte morphogenesis and ECM assembly at MTJs, and 2) Itg and Tgfb signaling in response to mechanical load regulates Scx, Mkx and Tnmd expression during the formation of MTJs.
Aim 1 is to visualize tendon progenitors in living wild-type, Mkx and Tnmd mutant embryos.
Aim 2 is to study roles for Itg and Tgfb signaling in regulation of Scx, Mkx and Tnmd expression.
Aim 3 is to study the roles of Itg and Tgfb signaling in response to mechanical load.
Each aim combines novel genetic manipulation, fluorescence dynamics imaging and quantitative methods for physiological stimulation of muscles to get at the mechanisms of ECM assembly at these specialized connective tissue structures.

Public Health Relevance

The proposed studies will provide one of the first models for how interactions between muscles and tendons influence assembly of the extracellular matrix to form a functional muscle attachment. Understanding formation and maintenance of myotendinous junctions will enhance our ability to develop pharmacological treatments for tendon injuries and produce stem/progenitor cells to repair damaged tendons and ligaments. Numerous human 'tendonopathies', are also associated with connective tissue defects.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR067797-05
Application #
9882216
Study Section
Skeletal Muscle and Exercise Physiology Study Section (SMEP)
Program Officer
Kirilusha, Anthony G
Project Start
2016-03-01
Project End
2021-02-28
Budget Start
2020-03-01
Budget End
2021-02-28
Support Year
5
Fiscal Year
2020
Total Cost
Indirect Cost
Name
University of California Irvine
Department
Anatomy/Cell Biology
Type
Schools of Arts and Sciences
DUNS #
046705849
City
Irvine
State
CA
Country
United States
Zip Code
92617
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