Fine structure and development of the collar enamel in gars, Lepisosteus oculatus, Actinopterygii

Abstract

The fine structure of collar enamel and the cells constituting the enamel organ during amelogenesis in Lepisosteus oculatus was observed by light, scanning electron and transmission electron microscopy. In the enamel, slender crystals were arranged perpendicular to the surface and the stripes that were parallel to the surface were observed, suggesting that the enamel in Lepisosteus shares common morphological features with that in sarcopterygian fish and amphibians. Ameloblasts containing developed Golgi apparatus, rough endoplasmic reticulum (rER) and secretory granules were found in the secretory stage. In the maturation stage, a ruffled border was not seen at the distal end of the ameloblasts, while many mitochondria and lysosome-like granules were obvious in the distal cytoplasm. The enamel organ consisted of the outer dental epithelial cells, stratum reticulum cells and ameloblasts, but there was no stratum intermedium. It is likely that the ameloblasts have less absorptive function in comparison with the inner dental epithelial cells facing cap enameloid.

Fine structural and immunohistochemical detection of collar enamel in the teeth of Polypterus senegalus, an actinopterygian fish

“…The morphological features of the collar enamel in Polypterus closely resemble those of the collar enamel in Lepisosteus (Sasagawa et al 2008) and of the non-prismatic enamel in lungfish, coelacanths and amphibians (Schmidt and Keil 1971;Smith and Miles 1971;Shellis and Poole 1978;Smith 1978;Sasagawa et al 1984;Satchell et al 2000). However, the collar enamel layer in Polypterus (500 nm to 1 μm) is thin in comparison with those found in Lepisosteus (5 μm; Sasagawa et al 2008) and in lungfish, coelacanths and amphibians (6-8 μm; Smith and Miles 1971;Sasagawa et al 1984;Satchell et al 2000). In addition, the collar enamel in Polypterus is probably only produced in a limited area of the tooth shaft near to the cap enameloid.…”

“…In extant actinopterygians, collar enamel has only been described in Lepisosteus (gars), once by electron microscopy (Prostak et al 1989) and twice by immunohistochemistry (Ishiyama et al 1999). In Lepisosteus, morphological data suggest that collar enamel shares common features with those of the enamel found in sarcopterygians and amphibians (Sasagawa et al 2008). Immunohistochemical observations have indicated that the enamel matrix in Lepisosteus contains domains that closely resemble those occurring in mammalian amelogenins, whereas immunoblot studies have demonstrated that the amelogenins of mammals are not present in the enamel proteins of Lepisosteus (I.…”

Tooth enamel and enameloid in actinopterygian fish

“…In the enamel layer, slender crystallites are arranged perpendicular to the surface, but do not make marked bundles (aprismatic enamel). Several stripes that lie almost parallel to the surface are usually observed in the section, implying that the stripes are incremental lines and indicating centrifugal growth [32,33,[37][38][39]44,45] (Fig. 6).…”

“…Collar enamel was initially noted in fossilized actinopterygians [32,33] and has also been reported in some living species, including Lepisosteus and Polypterus [34][35][36][37] (Figs. 5 and 6).…”

“…During the maturation stage, ameloblasts do not have a ruffled border at their distal end, although many mitochondria and lysosomal granules are obvious in their distal cytoplasm. This suggests that ameloblasts in fish have lower absorptive abilities in comparison with those present during the maturation stage in mammals [37,43] (Figs. 8 and 9).…”