On the origin of ganoine: Histological and ultrastructural data on the experimental regeneration of the scales of Calamolchthys calabaricus (osteichthyes, brachyopterygii, polypteridae)

Abstract

In order to understand the process of anoine formation on the ganoid scales, scale regener-ation has been studied to overcome the lack of a growth cries of scale ontogeny. Seven stages of ganoid scale regeneration have been defined over a period of five months in the polypterid fish Calamoichthys calabariits. The study has been carried out using transmission electron microscopic techniques. After wound healing and differentiation of the osseous basal plate, a layer of vascular dentin is deposited at the upper surface of he basal plate owing to the presence there of odonto-ilasts closely applied to the dentin. When these cells nove away, a close contact is then established between he stratified epidermis and the regenerating scale. Nu-nerous alterations of the epidermal-dermal boundary occur until its disappearance and a thick layer of pre-canoine is formed. This layer is progressively mineral-zed; and finally an organic intermediate layer differentiates between the ganoine, which is a hyper-nineralized tissue, and the overlying epidermis.

This ultrastructural study demonstrates rather un-quivocally the involvement of the inner epidermal layer (EL) in the appearance and growth of the ganoine. It suggested that these epidennal cells can be compared functionally to the inner dental epithelium (IDE) described during mammal tooth morphogenesis. Consequently, our results allow us to propose that ganoine an be identified as true enamel, although additional lata are necessary to analyze the proteinaceous com-ponent of its organic matrix.