Early morphogenesis of lower cheek teeth in mice with gene defects.

Tooth number is reduced in humans and mice when compared to the presumed basic tooth formula in mammals. In the regions, where teeth had been suppressed during evolution, a supernumerary tooth can appear as a result of abnormal development. However development of a supernumerary tooth, as well as origin of other anomalies, cannot be directly investigated in human embryos. That is the development of a supernumerary tooth was studied in a mouse model of this anomaly. The aims of the thesis were focused to verifying the hypothesis: Development of the supernumerary tooth in mutant mice is based on the revitalization of the rudimentary primordia of the teeth suppressed during evolution. We compared the morphological and quantitative aspects of the developing epithelium of the largest rudimentary (premolar) tooth primordia, called MS and R2, in the mandibles of WT, Spry2-/- , Spry4-/- , Spry2-/- ;Spry4-/- and Tabby mutant mice. Similarly, the upper incisor in WT mice was analysed and compared to the development of the duplicated incisor in Spry2+/- ;Spry4-/- mutant mice. In comparison to controls, decreased cell apoptosis and increased cell proliferation together with an enlarged volume of the dental epithelium were found during rudimentary tooth development in Spry mutant mice. These changes showed the..