Tubule formation and elemental detection in developing opossum enamel

Area of Science:

• Developmental Biology
• Paleontology
• Biomineralization

Background:

• Marsupial and some placental mammal enamel features tubules, with their cellular origin previously studied.
• The American opossum (Didelphis virginiana) serves as a model for understanding enamel tubule development.

Purpose of the Study:

• To investigate the structure and composition of enamel tubules in the American opossum during development.
• To compare the opossum's enamel matrix with that of placental mammals lacking enamel tubules.

Main Methods:

• Utilized conventional transmission electron microscopy (TEM) and high voltage electron microscopy (HVEM).
• Employed electron probe x-ray microanalysis (EPMA), selected-area electron diffraction (SAED), and electron spectroscopic imaging (ESI).
• Examined tissues prepared by aqueous (decalcified/undecalcified) and anhydrous (undecalcified) methods.

Main Results:

• Opossum enamel tubules originate from cytoplasmic remnants of Tomes' processes of ameloblasts.
• Sulfur is detected around and within tubules, suggesting sulfated glycoproteins or proteoglycans.
• Calcium/phosphorus (Ca/P) ratios in the mineralizing matrix are high and decrease with maturation.
• Calcium and phosphorus are present within tubules, potentially inhibited from mineralization by sulfated groups.

Conclusions:

• Opossum enamel tubules are formed by ameloblast remnants and contain sulfur-rich molecules.
• These molecules may play a role in regulating mineralization within the enamel tubules.
• The findings offer insights into the evolution and structure of mammalian enamel.