title: A role for hedgehog signaling in the differentiation of the insertion site of the patellar tendon in the mouse.
abstract: Tendons are typically composed of two histologically different regions: the midsubstance and insertion site. We previously showed that Gli1, a downstream effector of the hedgehog (Hh) signaling pathway, is expressed only in the insertion site of the mouse patellar tendon during its differentiation. To test for a functional role of Hh signaling, we targeted the Smoothened (Smo) gene in vivo using a Cre/Lox system. Constitutive activation of the Hh pathway in the mid-substance caused molecular markers of the insertion site, e.g. type II collagen, to be ectopically expressed or up-regulated in the midsubstance. This was confirmed using a novel organ culture method in vitro. Conversely, when Smo was excised in the scleraxis-positive cell population, the development of the fibrocartilaginous insertion site was affected. Whole transcriptome analysis revealed that the expression of genes involved in chondrogenesis and mineralization was down-regulated in the insertion site, and expression of insertion site markers was decreased. Biomechanical testing of murine adult patellar tendon, which developed in the absence of Hh signaling, showed impairment of tendon structural properties (lower linear stiffness and greater displacement) and material properties (greater strain), although the linear modulus of the mutant group was not significantly lower than controls. These studies provide new insights into the role of Hh signaling during tendon development.
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio, United States of America.
authors.forename: Chia-Feng
authors.initials: CF
authors.lastname: Liu
authors.forename: Andrew
authors.initials: A
authors.lastname: Breidenbach
authors.forename: Lindsey
authors.initials: L
authors.lastname: Aschbacher-Smith
authors.forename: David
authors.initials: D
authors.lastname: Butler
authors.forename: Christopher
authors.initials: C
authors.lastname: Wylie
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D015153:Blotting, Western; D002454:Cell Differentiation; D049109:Cell Proliferation; D003598:Cytoskeletal Proteins / Q000502:physiology*; D005260:Female; D051445:Fibrocartilage / Q000166:cytology* / Q000378:metabolism; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism*; D007124:Immunoenzyme Techniques; D019426:Integrases; D051741:Kruppel-Like Transcription Factors / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009124:Muscle Proteins / Q000502:physiology*; D020411:Oligonucleotide Array Sequence Analysis; D009924:Organ Culture Techniques; D017847:Patellar Ligament / Q000166:cytology* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D000071676:Zinc Finger Protein GLI1
chemical_list: D015415:Biomarkers; D003598:Cytoskeletal Proteins; C498520:Gli1 protein, mouse; D053823:Hedgehog Proteins; D051741:Kruppel-Like Transcription Factors; D009124:Muscle Proteins; D012333:RNA, Messenger; C491050:Smtn protein, mouse; D000071676:Zinc Finger Protein GLI1; C045073:Cre recombinase; D019426:Integrases