Document Detail


Stepwise enforcement of the notochord and its intersection with the myoseptum: an evolutionary path leading to development of the vertebra?
MedLine Citation:
PMID:  16928203     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The notochord constitutes the main axial support during the embryonic and larval stages, and the arrangement of collagen fibrils within the notochord sheath is assumed to play a decisive role in determining its functional properties as a fibre-wound hydrostatic skeleton. We have found that during early ontogeny in Atlantic salmon stepwise changes occur in the configuration of the collagen fibre-winding of the notochord sheath. The sheath consists of a basal lamina, a layer of type II collagen, and an elastica externa that delimits the notochord; and these constituents are secreted in a specific order. Initially, the collagen fibrils are circumferentially arranged perpendicular to the longitudinal axis, and this specific spatial fibril configuration is maintained until hatching when the collagen becomes reorganized into distinct layers or lamellae. Within each lamella, fibrils are parallel to each other, forming helices around the longitudinal axis of the notochord, with a tangent angle of 75-80 degrees to the cranio-caudal axis. The helical geometry shifts between adjacent lamellae, forming enantiomorphous left- and right-handed coils, respectively, thus enforcing the sheath. The observed changes in the fibre-winding configuration may reflect adaptation of the notochord to functional demands related to stage in ontogeny. When the vertebral bodies initially form as chordacentra, the collagen lamellae of the sheath in the vertebral region are fixed by the deposition of minerals; in the intervertebral region, however, they represent a pre-adaptation providing torsional stability to the intervertebral joint. Hence, these modifications of the sheath transform the notochord per se into a functional vertebral column. The elastica externa, encasing the notochord, has serrated surfaces, connected inward to the type II collagen of the sheath, and outward to type I collagen of the mesenchymal connective tissue surrounding the notochord. In a similar manner, the collagen matrix of the neural and haemal arch cartilages is tightly anchored to the outward surface of the elastic membrane. Hence, the elastic membrane may serve as an interface between the notochord and the adjacent structures, with an essential function related to transmission of tensile forces from the musculature. The interconnection between the notochord and the myosepta is discussed in relation to function and to evolution of the arches and the vertebra. Contrary to current understanding, this study also shows that notochord vacuolization does not result in an increased elongation of the embryo, which agrees with the circular arrangement of type II collagen that probably only enables a restricted increase in girth upon vacuolization, not aiding elongation. As the vacuolization occurs during the egg stage, this type of collagen disposition, in combination with an elastica externa, also probably facilitates flexibility and curling of the embryo.
Authors:
Sindre Grotmol; Harald Kryvi; Roger Keynes; Christel Krossøy; Kari Nordvik; Geir K Totland
Related Documents :
15745233 - The histological aspects of fillers complications.
12653633 - Glucosaminyl n-deacetylase/n-sulphotransferases in heparan sulphate biosynthesis and bi...
11964183 - Stopped-flow kinetic analysis of long-chain fatty acid dissociation from bovine serum a...
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of anatomy     Volume:  209     ISSN:  0021-8782     ISO Abbreviation:  J. Anat.     Publication Date:  2006 Sep 
Date Detail:
Created Date:  2006-08-24     Completed Date:  2007-01-18     Revised Date:  2013-06-07    
Medline Journal Info:
Nlm Unique ID:  0137162     Medline TA:  J Anat     Country:  England    
Other Details:
Languages:  eng     Pagination:  339-57     Citation Subset:  IM    
Affiliation:
Department of Biology, University of Bergen, Norway. Grotmol@uib.no
Export Citation:
APA/MLA Format     Download EndNote     Download BibTex
MeSH Terms
Descriptor/Qualifier:
Animals
Collagen / metabolism
Embryo, Nonmammalian / metabolism,  physiology*
Microscopy, Electron, Scanning
Microscopy, Electron, Transmission
Morphogenesis / physiology
Movement
Notochord / growth & development*,  metabolism
Salmo salar / embryology*,  metabolism
Chemical
Reg. No./Substance:
9007-34-5/Collagen
Comments/Corrections

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


Previous Document:  Evidence of solitary chemosensory cells in a large mammal: the diffuse chemosensory system in Bos ta...
Next Document:  Regional variations in the density and arrangement of elastic fibres in the anulus fibrosus of the h...