Teeth and ganoid scales in Polypterus and Lepisosteus, the basic actinopterygian fish: An approach to understand the origin of the tooth enamel

Recent findings regarding the structure and development of jaw teeth and ganoid scales in the basic actinopterygians Polypterus and Lepisosteus have been summarized in the present review. The relationship between cap enameloid, collar enamel in teeth, and ganoine in scales has been studied to understand the evolution of hard tissues in lower vertebrates. Enameloid is a well-mineralized tissue that is formed by both odontoblasts and dental epithelial cells and is found within the outermost layer of dentin. The inner dental epithelial cells surrounding the enameloid maintain the ability to produce amelogenin-like proteins; however, this may be a rudimentary function. The collar enamel of Polypterus and Lepisosteus exhibits marked immunoreactivity to anti-mammalian amelogenin antibodies, suggesting that it accommodates amelogenin-like proteins. It is likely that the collar enamel in basic actinopterygians corresponds to the enamel in sarcopterygians and amphibians. The recent fine structural and developmental studies have shown that the ganoine of ganoid scales in Polypterus and Lepisosteus is an enamel-like tissue. Positive immunoreactivity to the anti-mammalian amelogenin antibodies by the preganoine of both Polypteridae and Lepisosteidae supports that ganoine is a homolog of tooth enamel.