Distribution patterns of DNA template activity in the embryonic tooth organ: an acridine orange ultracytochemical study.

The ultracytochemical acridine orange (AO) method has been employed to demonstrate DNA template activity within embryonic incisor tooth organs excised from New Zealand White rabbits during the 25th day of gestation. Survey ultrastructural examination revealed characteristic distribution patterns of AO positive cell populations in the inner and outer enamel epithelium and the adjacent ectomesenchyme of the cervical loop region and in populations of fibroblast-like cells connecting as a band the outer AO positive cell groups. With increasing differentiation of ameloblasts and odontoblasts the number of AO positive cells as well as the number of AO chromatin interaction products per single cell nucleus decreased. Treatment with RNase prior to incubation with AO did not result in a noticeable loss of AO chromatin interaction products suggesting that RNA is negligible as a target for AO. The present results and comparison with other biological system indicated that interaction of AO with DNA sites coding for RNA appears to be restricted to specific templates in particular physiological conditions, e.g., stimulation of cells prior to differentiation by extracellular factors.