title: Remodeling of the notochord during development of vertebral fusions in Atlantic salmon (Salmo salar).
abstract: Histological characterization of spinal fusions in Atlantic salmon (Salmo salar) has demonstrated shape alterations of vertebral body endplates, a reduced intervertebral space, and replacement of intervertebral cells by ectopic bone. However, the significance of the notochord during the fusion process has not been addressed. We have therefore investigated structural and cellular events in the notochord during the development of vertebral fusions. In order to induce vertebral fusions, Atlantic salmon were exposed to elevated temperatures from fertilization until they attained a size of 15g. Based on results from radiography, intermediate and terminal stages of the fusion process were investigated by immunohistochemistry and real-time quantitative polymerase chain reaction. Examination of structural extracellular matrix proteins such as Perlecan, Aggrecan, Elastin, and Laminin revealed reduced activity and reorganization at early stages in the pathology. Staining for elastic fibers visualized a thinner elastic membrane surrounding the notochord of developing fusions, and immunohistochemistry for Perlecan showed that the notochordal sheath was stretched during fusion. These findings in the outer notochord correlated with the loss of Aggrecan- and Substance-P-positive signals and the further loss of vacuoles from the chordocytes in the central notochord. At more progressed stages of fusion, chordocytes condensed, and the expression of Aggrecan and Substance P reappeared. The hyperdense regions seem to be of importance for the formation of notochordal tissue into bone. Thus, the remodeling of notochord integrity by reduced elasticity, structural alterations, and cellular changes is probably involved in the development of vertebral fusions.
authors.affiliation: Nofima Marine AS, Fisheries and Aquaculture Research, Norwegian Institute of Food, P.O. Box 5010, Aas N-1432, Norway.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Ytteborg
authors.forename: Jacob Seilø
authors.initials: JS
authors.lastname: Torgersen
authors.forename: Mona E
authors.initials: ME
authors.lastname: Pedersen
authors.forename: Grete
authors.initials: G
authors.lastname: Baeverfjord
authors.forename: Kirsten O
authors.initials: KO
authors.lastname: Hannesson
authors.forename: Harald
authors.initials: H
authors.lastname: Takle
mesh_terms: D053674:Aggrecans / Q000096:biosynthesis / Q000235:genetics; D000818:Animals; D016723:Bone Remodeling / Q000502:physiology*; D004547:Elastic Tissue / Q000033:anatomy & histology; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D009672:Notochord / Q000033:anatomy & histology* / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D020317:Salmo salar / Q000033:anatomy & histology / Q000254:growth & development*; D013131:Spine / Q000254:growth & development* / Q000378:metabolism*; D013373:Substance P / Q000096:biosynthesis / Q000235:genetics
chemical_list: D053674:Aggrecans; D016326:Extracellular Matrix Proteins; D013373:Substance P