title: Replacing Shox2 with human SHOX leads to congenital disc degeneration of the temporomandibular joint in mice.
abstract: The temporomandibular joint (TMJ) consists in the glenoid fossa arising from the otic capsule through intramembranous ossification, the fibrocartilaginous disc and the condyle, which is derived from the secondary cartilage by endochondral ossification. We have reported previously that cranial neural-crest-specific inactivation of the homeobox gene Shox2, which is expressed in the mesenchymal cells of the maxilla-mandibular junction and later in the progenitor cells and perichondrium of the developing chondyle, leads to dysplasia and ankylosis of the TMJ and that replacement of the mouse Shox2 with the human SHOX gene rescues the dysplastic and ankylosis phenotypes but results in a prematurely worn out articular disc. In this study, we investigate the molecular and cellular bases for the prematurely worn out articular disc in the TMJ of mice carrying the human SHOX replacement allele in the Shox2 locus (termed Shox2 (SHOX-KI/KI)). We find that the developmental process and expression of several key genes in the TMJ of Shox2 (SHOX-KI/KI) mice are similar to that of controls. However, the disc of the Shox2 (SHOX-KI/KI) TMJ exhibits a reduced level of Collagen I and Aggrecan, accompanied by increased activities of matrix metalloproteinases and a down-regulation of Ihh expression. Dramatically increased cell apoptosis in the disc was also observed. These combinatory cellular and molecular defects appear to contribute to the observed disc phenotype, suggesting that, although human SHOX can exert similar functions to mouse Shox2 in regulating early TMJ development, it apparently has a distinct function in the regulation of those molecules that are involved in tissue homeostasis.
authors.affiliation: Academy of Integrative Medicine, Fujian University of Traditional Chinese Medicine, Fuzhou, Fujian, 350122, People's Republic of China.
authors.forename: Xihai
authors.initials: X
authors.lastname: Li
authors.forename: Hongbing
authors.initials: H
authors.lastname: Liu
authors.forename: Shuping
authors.initials: S
authors.lastname: Gu
authors.forename: Chao
authors.initials: C
authors.lastname: Liu
authors.forename: Cheng
authors.initials: C
authors.lastname: Sun
authors.forename: Yuqian
authors.initials: Y
authors.lastname: Zheng
authors.forename: Yiping
authors.initials: Y
authors.lastname: Chen
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D004204:Joint Dislocations / Q000151:congenital*; D020782:Matrix Metalloproteinases / Q000378:metabolism; D051379:Mice; D055758:SOX9 Transcription Factor / Q000378:metabolism; D000074122:Short Stature Homeobox Protein; D019224:Temporomandibular Joint Disc / Q000201:enzymology / Q000473:pathology*
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D016326:Extracellular Matrix Proteins; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; C493716:Runx2 protein, mouse; C106071:SHOX protein, human; D055758:SOX9 Transcription Factor; D000074122:Short Stature Homeobox Protein; C484663:Shox2 protein, mouse; C527933:Sox9 protein, mouse; C514061:ihh protein, mouse; D020782:Matrix Metalloproteinases