Follicular Apoptosis in a c-fos Knock-out Murine Model during Tooth Eruption

Tooth eruption is a complex and multifactorial process that is precisely timed during normal development. Previous studies have shown that apoptosis occurs in the follicular cells during normal tooth eruption and appears to be a critical step of that process. The proto-oncogen c-fos has been suggested to play a "third-messenger" role in the initiation of apoptosis in other systems and the availability of a c-fos knock out mouse model allows to test this hypothesis. The purpose of this study was to stage the development of the mandibular first molar and to compare the distribution of apoptotic changes in the dental follicle of first mandibular molars in homozygous and heterozygous animals. Mandibles were obtained from 2, 5, 9, 11 days old heterozygous and homozygous animals and fixed in 4% paraformaldehyde. Specimens 9 days and older were decalcified in 0.5M aqueous EDTA. Specimens were then dehydrated and embedded in paraffin and 7u sections were obtained. Apoptotic cells were stained using a digoxigenin-based in situ technique (Gavrieli et al, 1992). The ApoTag in situ apoptosis detection kit from Intergen was used in this study. Positive controls were provided by in situ staining of female rodent mammary gland. The results from our study showed that apoptosis was not observed in the coronal aspect of the dental follicle of 2 days old homozygous animals. Some cells showed signs of apoptosis on the lateral aspect of the dental follicle of 2 days old heterozygous animals. Samples obtained from 9 and 11 days old homozygous and heterozygous animals showed the presence of apoptotic cells in the coronal and lateral aspects of the dental follicle with a higher concentration in heterozygous animals.