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.

Histology and histochemistry of the gekkotan notochord and their bearing on the development of notochordal cartilage

“…We conclude that chondroid cells are derived directly from preexisting notochordal cells, most likely chordocytes (although notochordal epithelial cells cannot be excluded at this time). This is similar to the pattern observed in some teleosts, where notochordal cells appear to be precursors to chondrocytes under pathological conditions (Witten et al,2005; Ytteborg,2010) and during caudal regeneration (Kirschbaum and Meunier,1981).…”

Soft Texture of Atlantic Salmon Fillets Is Associated with Glycogen Accumulation

“…Permeabilization was carried out using 1% Triton in PBST for 20 min, before blocking in 2% dried milk diluted in PBST. Salmon specific Col I (Biologo, Germany), Perlecan (Chemicon, Germany) [19] and Aggrecan (Santa Cruz Biotechnology, USA) [19] primary antibodies were diluted in PBST and subjected to 3 min intermittent microwave incubation at 195 W [20]. The sections were washed thoroughly in PBST before incubation with Alexa conjugated secondary antibodies (Life Technologies Ltd, UK) as described above.…”

Four stages characterizing vertebral fusions in Atlantic salmon

“…However, cellular and molecular events during pathological bone development in salmon have been little described and only a few studies have been published (e.g. Wargelius et al., 2010a,b; Ytteborg et al., 2010a,b,c). Our group recently finished a comprehensive study on temperature induced vertebral fusions in Atlantic salmon, where we described various stages of pathological development using molecular tools.…”