Neural Crest Contributions to Dental Pulp Stem/Progenitor Cells and Craniofacial Structures: Alveolar Processes, Tongue and Temporomandibular Joint

Background: The cranial neural crest, a transient embryonic structure in vertebrates, is crucial to craniofacial and dental development. Populations of multipotent stem cells have been identified in various dental tissues including dental pulp. Hence, identification of multipotent cells of neural crest lineage within dental pulp and delineation of neural crest contributions to various craniofacial tissues may be a step towards utilizing the potential of neural crest progenitor cells for therapeutic applications. Objective: The overall purpose of the study was to identify a population of dental pulp stem/progenitor cells of neural crest lineage and demonstrate their neural differential potential and to evaluate neural crest contributions to alveolar bone, temporomandibular joint, and tongue using a transgenic gene knockout mouse model. Method: Transgenic mice were generated using Cre/lox system, which produced Cre-mediated recombination resulting in ß-galactosidase (X-gal) staining specifically in neural crest derived tissues, and sections from various craniofacial tissues were analyzed. Cells from dental pulp of these transgenic mice were cultured in a neurogenic medium to assay neurosphere formation and X-gal staining was performed. Wild type mice were also subjected to the same procedures to serve as controls. Results: Dental pulp cells were cultured for several months. Our analysis demonstrated that neural crest derived cells, as well as cells with mesodermal origin, were present in the cultures and demonstrated positive X-gal staining. Condensation of neural crest derived tissue was seen in the mesenchyme underlying tongue epithelium, dental follicle, dental papilla, nerve ganglia in the tongue cross section, trigeminal ganglion, connective tissue in the palate, alveolar bone, Meckel’s cartilage, hyoid bone, hyaline cartilage and the area of TMJ demonstrated the highly positive staining. Conclusions: This study suggests that: (1) neural crest-derived stem/progenitor cells are present in the dental pulp of embryonic and postnatal transgenic mice, (2) dental pulp cells form neurospheres when cultured under neurosphere forming conditions (Neurobasal A, B-27, EGF, bFGF), (3) neural crest derived cells as well as cells with mesodermal origin are present in the cultures, and (4) neural crest cells contribute in the formation of alveolar processes, tongue and the area of temporomandibular joint in embryonic as well as postnatal mice