Ameloblasts express type I collagen during amelogenesis.

Enamel and enameloid, the highly mineralized tooth-covering tissues in living vertebrates, are different in their matrix composition. Enamel, a unique product of ameloblasts, principally contains enamel matrix proteins (EMPs), while enameloid possesses collagen fibrils and probably receives contributions from both odontoblasts and ameloblasts. Here we focused on type I collagen (COL1A1) and amelogenin (AMEL) gene expression during enameloid and enamel formation throughout ontogeny in the caudate amphibian, Pleurodeles waltl. In this model, pre-metamorphic teeth possess enameloid and enamel, while post-metamorphic teeth possess enamel only. In first-generation teeth, qPCR and in situ hybridization (ISH) on sections revealed that ameloblasts weakly expressed AMEL during late-stage enameloid formation, while expression strongly increased during enamel deposition. Using ISH, we identified COL1A1 transcripts in ameloblasts and odontoblasts during enameloid formation. COL1A1 expression in ameloblasts gradually decreased and was no longer detected after metamorphosis. The transition from enameloid-rich to enamel-rich teeth could be related to a switch in ameloblast activity from COL1A1 to AMEL synthesis. P. waltl therefore appears to be an appropriate animal model for the study of the processes involved during enameloid-to-enamel transition, especially because similar events probably occurred in various lineages during vertebrate evolution.

Inductest and spermatest in genetic toxicology testing.

Bacterial strains have been especially devised to measure the ability of chemicals to induce phage development. This type of test named Inductest, responds in general to DNA damaging agents. Metabolic activation can be used and good sensitivities are achieved. Variations of the Inductest exist: some have short time responses (1 h or less) or allow to look at phage mutagenesis as well. Some compounds elicit a response in Inductest and not in the bacterial mutagenesis assay (Mutatest). The reverse is also true and may be more frequent. The sperm abnormality assay (Spermatest) consists in examining by visual scoring of sperm shape if an agent is able to damage in vivo mammalian germ cells. Such agents are in general able to interfere with the normal differenciation of sperm cells so that genetic damage is probably not the only end point of the assay. The spermatest yields false negative but few false positive for carcinogenicity. It can be used directly to monitor human populations. Both tests, have probably not yet reached their full development.

Adaptation of the salmonella/mammalian microsome test to the determination of the mutagenic properties of mineral oils.

Two techniques allowing the determination of the mutagenicity of lipophilic compounds such as mineral oils with the Ames test have been developed by using benzo[a]pyrene (BP) dissolved in white oil as a synthetic reference oil. The first technique involves prior extraction of polynuclear aromatic hydrocarbons (PAH) with dimethyl sulfoxide. In the second method, which proved simpler and of more general use, the compounds to be tested are directly dispersed in aqueous medium with Tween 80. The use of these techniques made possible the study of mutagenicity of various kinds of mineral oil. Mutagenic activity was found in used crankcase oils, and also in petroleum distillates but much less in solvent-refined oils. A good correlation was observed between mutagenic activity and PAH content but not BP content of oils. Because of their peculiar response to the test, petroleum distillates were studied in more detail. When added in low amounts to pure PAH compounds such as BP, they enhanced its mutagenic activity (enhancement). When added in higher amounts, on the contrary, these oils completely inhibited BP mutagenic activity (inhibition effect). Both effects correlated well with the PAH content and the mutagenic activity of the petroleum distillates tested. These results explain the abnormal dose-response curves curves obtained with these petroleum distillates and the negative results regarding their mutagenic activity reported in earlier studies. A likely explanation is discussed for the enhancement and inhibition effects.