Spatial organization of collagen in annelid cuticle: order and defects

Abstract

The epidermis of Paralvinella grasslei (Polychaete, Annelida) is covered by an extracellular matrix, the cuticle, mainly composed as in other annelids of superimposed layers of non-striated collagen fibrils. The collagen fibrils of annelid cuticle are shown to be composed of parallel and sinuous microfibrils (thin sections and freeze-fracture replicas). The 3-dimensional organization of collagen is characterized by 2 different types of geometrical order: (a) Fibrils form a quasiorthogonal network, whose structure is comparable to that of a "plywood"; (b) Fibrils are helical, and goniometric studies show that microfibrils present a definite order within each fibril, which is termed "cylindrical twist". These 2 characteristics are those which have recently been evidenced in "blue phases", i.e., liquid crystals which are closely related to cholesteric liquid crystalline phases. Non-fluid analogues of cholesteric liquids are widespread among invertebrate cuticles and the presence of blue phase analogues suggests that a self-assembly mechanisms is involved in cuticle morpho-genesis, which is derived from that governing blue phase growth. The cuticular network presents local rearrangements of fibrils called "defects", despite the fact that they are elaborate structures which trigonal and pentagonal singularities. Branched fibrils are regularly observed. We discuss the involvement of these pattern disruptions in the cuticle growth process.

Blue-phase drops on a glass interface and their decoration at the cholesteric transition

“…Oblique sections of such structures reproduce the patterns observed in blue-phase drops, at the cholesteric transition. Studies of collagen distribution in the skin of certain worms [23,24] show other examples of structures very close to the model due to Meiboom et al [9], but there are some differences with respect to that model: a. Vertical fibrils are absent, or strongly reduced, or even replaced by a thin cytoplasmic extensions (Fig. 7d).…”

Comparative study of the cuticle in some aquatic oligochaetes (Annelida: Clitellata)

“…Its fibers display, however, an undulating pattern and are not like earlier descriptions of enchytraeids and lumbricids. Regularly undulating cuticular fibers are also observed in the polychaetes Paralvinella grasslei and Alvinella pompejana, both living in ecosystems associated with deep-sea hydrothermal vents (Gaill and Bouligand, 1987;Lepescheux, 1988).…”

Ordre quasicristallin dans les matrices extracellulaires

“…L'examen d6taill6 des figures obtenues sur des coupes fines de ces structures et analys6e au microscope 61ectronique ~ transmission a permis de reconstituer l'architecture fondamentale qui est celle d'un contreplaqu6 r6guli~rement torsad6 ( fig. De telles analogies on 6t6 6tendues ~t plusieurs types de mat6riels biologiques 6tudi6s in vivo ou in vitro, tel que I'ADN (Livolant, 1986), le collag~ne (Giraud-Guille, 1989), la cellulose (Roland et al, 1989) et l'6tude de ces mat6riels a illustr6e la richesse de ces analogies en r6v61ant la vari6t6 et la diversit6 des formes d'organisations biologiques (Giraud et al, 1978;Livolant et al, 1989;Lepescheux, 1988;Gaill & Bouligand, 1987ab) pr6sentant des ordres ~t longue distance. Cette structure est constitu6e de strates fibrillaires parall~les, l'orientation fibrillaire de chaque state varie d'un angle constant et tr~s petit dans le sch6ma mais en fair la structure est continue et le d6coupage en plan successifs n'a lieu que pour les besoins de la repr6sentation.…”