title: Mineralization of the vertebral bodies in Atlantic salmon (Salmo salar L.) is initiated segmentally in the form of hydroxyapatite crystal accretions in the notochord sheath.
abstract: We performed a sequential morphological and molecular biological study of the development of the vertebral bodies in Atlantic salmon (Salmo salar L.). Mineralization starts in separate bony elements which fuse to form complete segmental rings within the notochord sheath. The nucleation and growth of hydroxyapatite crystals in both the lamellar type II collagen matrix of the notochord sheath and the lamellar type I collagen matrix derived from the sclerotome, were highly similar. In both matrices the hydroxyapatite crystals nucleate and accrete on the surface of the collagen fibrils rather than inside the fibrils, a process that may be controlled by a template imposed by the collagen fibrils. Apatite crystal growth starts with the formation of small plate-like structures, about 5 nm thick, that gradually grow and aggregate to form extensive multi-branched crystal arborizations, resembling dendritic growth. The hydroxyapatite crystals are always oriented parallel to the long axis of the collagen fibrils, and the lamellar collagen matrices provide oriented support for crystal growth. We demonstrate here for the first time by means of synchroton radiation based on X-ray diffraction that the chordacentra contain hydroxyapatite. We employed quantitative real-time PCR to study the expression of key signalling molecule transcripts expressed in the cellular core of the notochord. The results indicate that the notochord not only produces and maintains the notochord sheath but also expresses factors known to regulate skeletogenesis: sonic hedgehog (shh), indian hedgehog homolog b (ihhb), parathyroid hormone 1 receptor (pth1r) and transforming growth factor beta 1 (tgfb1). In conclusion, our study provides evidence for the process of vertebral body development in teleost fishes, which is initially orchestrated by the notochord.
authors.affiliation: Department of Biology, University of Bergen, Bergen, Norway. Shou.Wang@bio.uib.no
authors.forename: Shou
authors.initials: S
authors.lastname: Wang
authors.forename: Harald
authors.initials: H
authors.lastname: Kryvi
authors.forename: Sindre
authors.initials: S
authors.lastname: Grotmol
authors.forename: Anna
authors.initials: A
authors.lastname: Wargelius
authors.forename: Christel
authors.initials: C
authors.lastname: Krossøy
authors.forename: Mattias
authors.initials: M
authors.lastname: Epple
authors.forename: Frank
authors.initials: F
authors.lastname: Neues
authors.forename: Tomasz
authors.initials: T
authors.lastname: Furmanek
authors.forename: Geir K
authors.initials: GK
authors.lastname: Totland
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000033:anatomy & histology; D015415:Biomarkers / Q000378:metabolism; D002113:Calcification, Physiologic / Q000502:physiology*; D003094:Collagen / Q000648:ultrastructure; D017886:Durapatite / Q000032:analysis*; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D009672:Notochord / Q000000981:diagnostic imaging / Q000502:physiology*; D020317:Salmo salar / Q000033:anatomy & histology / Q000502:physiology*; D013131:Spine / Q000033:anatomy & histology / Q000502:physiology*; D014463:Ultrasonography; D014961:X-Ray Diffraction
chemical_list: D015415:Biomarkers; D036341:Intercellular Signaling Peptides and Proteins; D003094:Collagen; D017886:Durapatite
keywords: collagen; hydroxyapatite; mineralization; notochord; salmon