Methods: Mice from normal and mutant group were sacrified 7,10,14 days after birth, then tibia and maxilla including the first molar were excised. Samples were examined histologically and ultrastructurally.
Results: In both tibia and maxilla, the number of osteoclast in mi mice decreased and size of cell was smaller than those of normal mice. Although mutant osteoclast showed generally mononuclear and less activity for TRAP staining, some osteoclasts at the alveolar bone were multinuclear and heavy intencity for TRAP activity.
Ultrastructurally, osteoclasts at the alveolar bone in mi mice were multinuclear, including cytoplasmic vacuolization, but these osteoclasts attached tightly at the bone surfaces and had poorly developed ruffled borders and clear zone compared to those of normal mice.
Conclusion: These data demonstrate that the initial osteoclast differentiation including cell-fusion and TRAP activity is induced at alveolar bone surface during tooth eruption in mi mice, but these osteoclasts show impaired bone resorption due to poorly developed ruffled borders. It suggests that MITF is essential for full development of osteoclast.