Parabolic pattern of a peculiar striated body in the tunic of the ascidian Halocynthia papillosa (Tunicate, Ascidiacea)
Van Daele, Y.; Gaill, F.; Goffinet, G. (1991). Parabolic pattern of a peculiar striated body in the tunic of the ascidian Halocynthia papillosa (Tunicate, Ascidiacea). J. Struct. Biol. 106(2): 115-124. https://dx.doi.org/10.1016/1047-8477(91)90081-7
In: Journal of structural biology. ACADEMIC PRESS INC ELSEVIER SCIENCE: San Diego, Calif.. ISSN 1047-8477; e-ISSN 1095-8657, more
Numerous extracellular striated bodies (SBs) are found in the basal region of the tunic of the ascidian Halocyrethia papillosa SBs appear as flattened ellipsoid globules (0.8 × 1.3 μm), the long axes of which run parallel to the cellulose fiber bundles of the tunic. SBs are made of a twisted arrangement of cylindrical fibrils that exhibit an electron-lucent core 6.5 nm in diameter, limited by an electron-dense sheath 1.5 nm in thickness. Unlike helicoidal systems described in other extracellular matrices, SBs are discrete and discontinuous plywoods. They are unique structures owing to the 390-nm periodical succession of isotropic and anisotropic layers and to the π/3 twist angle of the fibrils. The chemical composition of SBs is unknown. However, histochemical, immunostaining, contrasting, and goldlabeling methods suggest that they are at least partially composed of proteins and made of a composite material different from collagen, cellulose and glycosaminoglycans. The origin of SBs may be interpreted as a phase segregation between their own constitutive materials and tunical cellulose. Their distribution pattern correlates closely with the degree of disorganization of the helicoidal cellulose system.
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