CONTRIBUTION OF EARLY-EMIGRATING MIDBRAIN CREST CELLS TO THE DENTAL MESENCHYME OF MANDIBULAR MOLAR TEETH IN RAT EMBRYOS

Teeth are formed by reciprocal interactions between the epithelium and mesenchyme in the first pharyngeal arch. Although the contribution of midbrain and hindbrain crest cells to the first pharyngeal arch has b een previously examined in rodent embryos, no direct evidence exists t hat these cells are actually involved in the dental mesenchyme. In ord er to elucidate the contribution of the cranial neural crest cells in tooth formation, we first identified the emigration sites and stages p roviding the crest cells that migrate to the presumed tooth-forming re gion of the mandibular prominence. focal labeling with DiI was perform ed at the midbrain and anterior hindbrain crests in rat embryos, and t he labeled embryos were cultured for 30 or 60 hr. The resultant migrat ion patterns indicated that posterior midbrain crest cells emigrating by the end of the 4-somite stage predominantly migrated to the region where tooth buds normally develop. Second, we established a new type o f long-term culture system in which whole embryo culture is followed b y a mandibular organ culture. Using this system, rat embryos were main tained from the early-somite stage and the molars in the explants were able to reach the bud stage within 8 days. Finally, to ascertain if p osterior midbrain crest cells emigrating by the end of the 4-somite st age were involved in the dental mesenchyme, these cells were labeled w ith DiI and processed for the long-term culture. Labeled crest cells w ere clearly detectable in the dental mesenchyme. These findings indica te that the early-emigrating posterior midbrain crest cells contribute to mandibular molar tooth development in rat embryos. (C) 1996 Academ ic Press, Inc.