Sponge Gemmule Coats: Germanium(Ge) Modification of a Collagenous Structure
A few marine sponges and many freshwater species asexually develop small, dormant, reproductive, seed-like structures called gemmules which are bordered by a complex collagenous capsule, the gemmule coat (1). The morphogenesis of the coat includes a highly regular set of processes which provide an exceptional but rarely appreciated, model for investigating collagen secretion (2). Gemmule coats can act as barriers for the prevention of water loss from the internal cells and their differential permeability may provide the primary basis for dormancy regulation (3,4). Gemmule coats contain oriented silica structures embedded within them and thus morphologically suggest a possible relationship of silicon (Si) to collagen formation. Such has been demonstrated among vertebrates in which soluble forms of Si appear essential for normal collagen elaboration (5). Investigations which exclude Si from the experimental system are notoriously difficult to conduct and thus a related element, germanium (Ge), which can act either as a Si analogue (at low concentration) or as a competitive inhibitor of Si (at higher concentration), has been introduced as a tool for studying Si interactions and essentiality (6).
KeywordsCollagen Fibril Marine Sponge Coat Layer Freshwater Sponge Coat Formation
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