Ultrastructural Observations on the Intraodontoblastic Collagen Fibrils of the Mouse Tooth Germs

Collagens of most connective tissues are subject to continuous remodelling and turnover, a phenomenon which occurs under both physiological and pathological conditions. Degradation of these proteins involves participation of a variety of proteolytic enzymes including members of the following proteinase classes: matrix metalloproteinases (e.g. collagenase, gelatinase and stromelysin), cysteine proteinases (e.g. cathepsin B and L) and serine proteinases (e.g. plasmin and plasminogen activator). Convincing evidence is available indicating a pivotal role for matrix metalloproteinases, in particular collagenase, in the degradation of collagen under conditions of rapid remodelling, e.g. inflammation and involution of the uterus. Under steady state conditions, such as during turnover of soft connective tissues, involvement of collagenase has yet to be demonstrated. Under these circumstances collagen degradation is likely to take place particularly within the lysosomal apparatus after phagocytosis of the fibrils. We propose that this process involves the following steps: (i) recognition of the fibril by membrane-bound receptors (integrins?), (ii) segregation of the fibril, (iii) partial digestion of the fibril and/or its surrounding non-collagenous proteins by matrix metalloproteinases (possibly gelatinase), and finally (iv) lysosomal digestion by cysteine proteinases, such as cathepsin B and/or L. Modulation of this pathway is carried out under the influence of growth factors and cytokines, including transforming growth factor beta and interleukin 1 alpha.

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Changes in macromolecular organization in collagen assemblies during secretion in the nidamental gland and formation of the egg capsule wall in the dogfish Scyliorhinus canicula

1993

Phil. Trans. R. Soc. Lond. B

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The thickest layer (L 2 ) of the egg capsule wall of the dogfish, Scyliorhinus Canicula , is constructed largely from highly ordered collagen fibrils (Knight & Hunt 1976). This collagen is stored and secreted by the nidamental gland and passes through an extraordinary series of ordered phases, m any of which have well defined liquid crystalline structure. We have examined the changes in macromolecular packing of the collagen as it moves from the cisternae of the endoplasmic reticulum to secretory granules, is secreted and then formed into the egg capsule wall. Within the endoplasmic reticulum cisternae the collagen appears anisotropic but becomes assembled into a smectic A or lamellar phase in the Golgi cisternae. This phase persists in early secretory granules, where it is found in conjunction with a micellar phase. As these granules mature, the collagen passes through a cholesteric mesophase before adopting a columnar hexagonal arrangement. On merocrine secretion the granules’ contents revert rapidly to the smectic A-lamellar and micellar phases. As it passes along the nidamental gland tubules, the collagen is first converted into a second distinct micellar phase before assembling into the final fibrils that constitute the egg capsule. These phase transitions give powerful insights into the way in which the macromolecular arrangement of collagen molecules can be modulated and are discussed in the context of a range of other related structural transitions in collagens.

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Ultrastructural Observations on the Intraodontoblastic Collagen Fibrils of the Mouse Tooth Germs

Cited by 3 publications

References 12 publications

Role of the odontoblast process

Role of the odontoblast process

Phagocytosis and intracellular digestion of collagen, its role in turnover and remodelling

Changes in macromolecular organization in collagen assemblies during secretion in the nidamental gland and formation of the egg capsule wall in the dogfish Scyliorhinus canicula

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