“…As these ectodermally derived cells migrate, they contribute extensively to the formation of mesenchymal structures in the head and neck. Cell labeling studies have demonstrated that neural crest cells arising from rhombomeres 1-3 (r1-3) of anterior hindbrain migrate into the first branchial arch and, thereafter, reside within the maxillary and mandibular prominences (Osumi-Yamashita et al, 1990;Serbedzija et al, 1992;Bronner-Fraser, 1993;Selleck et al, 1993;Lumsden and Krumlauf, 1996). The migration of these rhombencephalic crest cells is regulated by growth factor signaling pathways and their downstream transcription factors before the CNC cells become committed to several different tissue types such as bone, cartilage, tooth, and cranial nerve ganglia (Noden, 1983(Noden, , 1991Lumsden, 1988;Graham and Lumsden, 1993;Le Douarin et al, 1993;Echelard et al, 1994;Imai et al, 1996;Trainor and Krumlauf, 2000).…”