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 ganoine formation on the ganoid scales, scale regeneration has been studied to overcome the lack of a growth series of scale ontogeny. Seven stages of ganoid scale regeneration have been defined over a period of five months in the polypterid fish Calamoichthys calabaricus. 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 the basal plate owing to the presence there of odontoblasts closely applied to the dentin. When these cells move away, a close contact is then established between the stratified epidermis and the regenerating scale. Numerous alterations of the epidermal-dermal boundary occur until its disappearance and a thick layer of pre-ganoine is formed. This layer is progressively mineralized; and finally an organic intermediate layer differentiates between the ganoine, which is a hyper-mineralized tissue, and the overlying epidermis. This ultrastructural study demonstrates rather unequivocally the involvement of the inner epidermal layer (IEL) in the appearance and growth of the ganoine. It is suggested that these epidermal 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 can be identified as true enamel, although additional data are necessary to analyze the proteinaceous component or its organic matrix.

Endocranial preservation of a Carboniferous actinopterygian from Lancashire, UK, and the interrelationships of primitive actinopterygians

“…Gardiner & Schae¡er (1989) used this as synapomorphy for Pteronisculus plus higher actinopterygians, but Richter & Smith (1995) argue that`prismatic ganoine' (Òrvig 1978) or`pseudoprismatic ganoine' (Òrvig 1967) is not a well-de¢ned feature of enamel structure. Ganoine itself is a poorly de¢ned term which is used to describe actinopterygian enamel (Sire et al 1987;Sire 1994). In primitive actinopterygians, enamel is deposited incrementally leaving a series of growth lines, and the terms`prismatic' and`pseudoprismatic' refer to arrangements of the constituent crystallites.…”

“…Whether these associations represent an actual, singular, episode in ¢n evolution or an arti¢cial coalescence which may be teased apart with the introduction of new data (as is apparent with endoskeletal ¢n characters) remains to be tested. More complete specimens of Cheirolepis and Dialipina would be particularly informative about early patterns of actinopterygian ¢n evolution, while investigations of ¢n ontogeny in cladistians and chondrosteans comparable to those already completed on Danio rerio (Smith et al 1994;Sordino et al 1995;Geraudie et al 1994) would illuminate the likely developmental underpinning of such anatomical transformations.…”

A reappraisal of the origin and basal radiation of the Osteichthyes

“…Enamel is present in sarcopts (Ørvig, 1951;Meinke and Thomson, 1983;Meinke, 1984;Chang and Smith, 1992;Richter and Smith, 1995;Zhu et al, 2006), whereas regeneration (Erpetoichthys: Sire et al, 1987;Lepisosteus: Sire, 1994) and histological studies (Richter and Smith, 1995) demonstrate actinopt 'ganoine' is enamel. Histologically indistinguishable hard tissues are found in some 'acanthodians' (Richter and Smith, 1995;Richter et al, 1999).…”

Histology of the heterostracan dermal skeleton: Insight into the origin of the vertebrate mineralised skeleton

“…Giles et al (2013) demonstrated that this dermal architecture is also plesiomorphic with respect to placoderms, regardless of whether they are perceived as monophyletic or paraphyletic. Osteichthyans possess comparable dermal skeletal architecture, although their tubercles are capped with ganoine or enamel [ganoine is a hypermineralised tissue developmentally comparable to enamel (Sire et al, 1987;Sire, 1994;Sire et al, 2009)]. Chondrichthyans, the sister group to all other crown-gnathostomes, possess dermal denticles capped with enameloid, thus the phylogenetic distribution of dermal skeletal capping tissues suggests ganoine is apomorphic with respect to osteichthyans.…”