Tubule formation and elemental detection in developing opossum enamel

Abstract

Most marsupials and some placental mammals possess enamel characterized by the presence of tubules, and the cellular origin of these structures has been the subject of a number of previous studies (See, for example, Lester, 1970; Azevedo and Goldberg, 1987). In the present report, tooth germs of the American opossum were examined to determine the structure and composition of enamel tubules during development and to analyze the enamel matrix relative to that of placental mammals with atubular enamel. For this purpose, tissues prepared by aqueous (decalcified and undecalcified) and anhydrous (undecalcified) methods were investigated by conventional transmission (TEM) and high voltage electron microscopy (HVEM), as well as by electron probe x-ray microanalysis (EPMA), selected-area electron diffraction (SAED), and electron spectroscopic imaging (ESI). Results indicate that most enamel tubules in the opossum begin as cytoplasmic remnants of Tomes' processes of ameloblasts. During development of the matrix, some of the tubules do not appear to be continuous throughout the prismatic layer. Sulfur is detectable around the lumen of the tubule in decalcified sections by EPMA and in and around the tubule by ESI. Calcium/phosphorus (Ca/P) molar ratios of the mineralizing matrix are generally higher than those found in enamel of other mammals and appear to decrease rather than increase with enamel maturation. The summary of data indicates the presence of sulfated glycoproteins or proteoglycans in this tissue, specifically around enamel tubules. Calcium and phosphorus are also present within the tubules, with the sulfated groups possibly binding calcium to prevent mineralization of the enamel tubules themselves.

Proteolytic activity of opossum tooth extracts

“…IC, D) . This pattern is identical to th at reported for the North Ameri ca n opos um , Didelphis virginiana (6). Marsupi al enamel is organized into pri ms, 2-5 mm in di ameter, that are penetrated by tubules less th an 0.1 -0.S,Ltm indiameter that contain membranou structures (7).…”

“…Opossum enamel crystals have been examined by electron probe microanalysi and by electron diffracti on, and co mprise hydroxya pati te crystals with a/ P molar rati o imilar to those ob erved in eutheri an mammals ( 6 ). The principal protei n in the opossum developing enamel matrix is amelo-Ryu et a/.…”

Biological Calcification

“…10.2 and shown in Fig. described them in the developing enamel of the shark Carcharhinus menisorrah, and Stern et al (1992) in that of the opossum. Even if named differently, structures morphologically identifiable as crystal ghosts have been reported in enamel since 1962. , using a PEDS-like method (the EDTA decalcification of sections followed by staining with a saturated uranyl acetate solution at pH 7.0), described crystal-like, long, fairly broad septa that were assumed to represent the enamel stroma on whose surfaces crystallites were formed, so that the septa eventually became embedded in the crystallites.…”

Plastic casts and confocal laser scanning microscopy applied to the observation of enamel tubules in the red Kangaroo (Macropus rufus)

“…At the late or final stage of matrix formation, ameloblasts show morphological transformations and their Tomes’ processes start to shorten (Reith, 1970; Inage, 1987; Suzuki et al ., 1999). As extended Tomes’ processes and small processes from these seem to participate in the tubule formation (Lester, 1970; Gilkeson and Lester, 1989; Stern et al ., 1992), the differences in terminal shapes might be due to the morphological changes in ameloblasts and Tomes’ processes at the later stage of matrix formation.…”

“…According to Stern et al . (1992), opossum enamel tubules, containing processes from ameloblasts, are sometimes broken and begin again during the development of enamel.…”