Development and cell fate in interspecific (Mus musculus/Mus caroli) orthotopic transplants of mouse molar tooth germs detected by in situ hybridization

Interpretation of results from previous tooth germ transplantation studies is limited by the inability to distinguish between donor and host cells unequivocally. Furthermore, ectopic transplantation sites have generally been used and the relevance of this to tooth development in situ is uncertain. The aim here was to determine cell fate in orthotopic tooth germ transplants using an interspecific mouse marker system. Mandibular first molar tooth germs were dissected from Mus musculus (CD1) and Mus caroli mice (age range 15–19 day embryo) and transplanted interspecifically into the alveolar crypt of extirpated first mandibular molars in neonatal M. musculus (CD1) and M. caroli hosts. Grafts were recovered at intervals up to 4 weeks postoperatively. Paraffin wax-embedded sections were examined using routine histological techniques and in situ hybridization with a biotinylated DNA probe (pmSat5) specific for M. musculus, to distinguish between donor and host cells. Development of M. musculus tooth germs in M. caroli mandibles and vice versa was similar and transplants progressed to incipient root formation. Vascularization of transplants was chimaeric, being donor-derived in the pulp and host-derived more peripherally. The investing soft tissues comprised a mixture of donor and host cells, predominantly donor. Donor cells were also found in the soft tissue of intertrabecular spaces in the surrounding bone, but alveolar osteocytes were almost entirely host-derived. Long-term survival of grafts was limited and few donor cells were present after 2 weeks. This study provides an unequivocal demonstration of the origin of all cells present in transplanted tooth germs.