Molecular characterization of human impacted third molars: diversification of compartments.

To gain more insight into the development of human teeth, we characterized different compartments of impacted third molars at two developmental stages by assessing expression levels of a set of genes. We considered genes known to be essential for the development of teeth and ectomesenchyme as well as genes covering characteristic features of stemness. Molars were divided into the operculum, periodontal ligament, developing pulp and, using a new approach, the pad-like tissue beneath the developing pulp. Markers for ectomesenchyme and tooth development known from rodents were assayed by semiquantitative PCR and every compartment was assigned its own signature of gene expression. The expression of markers characteristic of stem cells pointed to multipotent features. The expression patterns found shift in the course of development underscoring the relevance of these genes involved in human tooth development. The results suggest an inherent asymmetry between the developing pulp and pad-like tissue established early in tooth development. A microarray analysis of cells derived from pad-like tissue and pulp proper was performed to obtain cues regarding the consequences of tissue diversification. Both sets of data support the validity of our new approach to the subdivision of the developing tooth, by indicating a compartment-dependent commitment of isolated cells probably due to the postulated asymmetry within the developing tooth germ.