Localization of ornithine decarboxylase in mouse teeth. An in vitro and in vivo study

Ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis, and thus in tissue growth and development, has been localized in mouse dental tissues, in vivo as well as in vitro by light and electron microscopic autoradiography with radiolabeled alpha-difluoromethylornithine ([3H]DFMO). Mandibular first molar germs from day-18 fetuses were incubated in vitro in the presence of [3H]DFMO and processed for autoradiography. For ODC localization in vivo, 3-day old puppies received [3H]DFMO by injection. As controls, puppies were injected either with unlabeled DFMO, or with cycloheximide before administration of isotope. Kidneys and mandibles were excised and processed for autoradiography. In vitro, labeling was found in all cell types of the tooth germ, but with a more intense labeling in ameloblasts and odontoblasts. In both these, radioactivity decreased from the tip of the cusps to the cervical loop. In vivo the binding of [3H]DFMO in cells of the ameloblast and odontoblast lineages, respectively, showed a gradual increase form the posterior end of the incisor to its anterior end. The distribution of radioactivity in the kidney was in accordance with findings by others. Both the kidney and tooth cell labeling decreased strongly after cycloheximide treatment. The results show that ODC is expressed in tooth-forming cells, and that ODC is not only present in differentiating cells but occurs at higher amounts in mature, secreting cells. The findings suggest that polyamines have a central role in tooth development.