Louise Zylberberg

Type I collagen in tetrapods is usually a heterotrimeric molecule composed of two α1 and one α2 chains. In some teleosts, a third α chain ha

The structure of the bony tubercles of the turbot, Scophthalmus maximus (L., 1758), was examined using ground sections, microradiography, SEM, and TEM. The tubercles are small, isolated, mineralized conical plates randomly distributed in the eyed side of the body. They are composed of three layers: the outer limiting layer, the external layer, and the basal plate, which make up the thin and flat elasmoid scales of Teleostei. The main difference between regular elasmoid scales and bony tubercles lies in the organization and the growth of the basal plate. Indeed, the conical shape of the tubercle is the result of a prominent thickening of the central part of the basal plate where the collagen matrix is organized in a complicated three‐dimensional network. Densely packed thick collagen fibrils form superimposed plies organized in a plywood‐like structure that resembles that of the elasmoid scales but it is criss‐crossed by numerous vertical sheets of thin collagen fibrils. The tubercles originate from thin and flat plates located in the skin of larvae and juveniles, whose structure is that of regular‐developing elasmoid scales. Thus, the tubercles of Scophthalmus maximus could be considered as modified elasmoid scales rather than bony structures. They might be the result of specific arrangements related to the general trend of reduction of the dermal skeleton in the teleostean lineage. J. Morphol. 258:84–96, 2003.

Background The account of the present study is to test our previous hypothesis that ganoine, a highly mineralized layer found at the scale surface of primitive actinopterygian fish, could be homologous with the enamel covering the crown of vertebrate teeth. Methods: Immunocytochemical techniques have been carried out on regenerating scales of a primitive polypterid, Calamoichthys calabaricus,with three antibodies to mammalian amelogenins. Results: The present study provides the first evidence that ganoine contains molecules which cross‐react with mammalian amelogenin proteins. Conclusions: This result is consistent with our previous findings that ganoine and enamel can be considered as homologous tissues. Moreover, the presence in ganoine of a primitive actinopterygian of amelogenin‐like proteins, which share epitopes with amelogenins of mammalian enamel, indicates that the gene(s) coding for these proteins appeared earlier than previously suggested and supports the hypothesis that amelogenins show a highly conserved structure through vertebrate evolution. Anat. Rec. 249:86–95, 1997.