![]() Indeed, NCCs from different rhombomeres remain spatially segregated through to late developmental stages, and contribute to skeletal elements of multi-rhombomeric origin forming cryptic intraskeletal interfaces ( Köntges and Lumsden, 1996). Maintaining the spatial segregation of such streams has an important impact on craniofacial pattern. ![]() 1A) ( Birgbauer et al., 1995 Kulesa and Fraser, 2000 Lumsden et al., 1991 Sechrist et al., 1993 Serbedzija et al., 1992 Shigetani et al., 1995 Trainor et al., 2002b). The NCC subpopulations that target individual PAs migrate in stereotypical streams ( Fig. NCCs that originate from the diencephalon and anterior mesencephalon (see Glossary, Box 1) migrate into the frontonasal process (FNP) (see Glossary, Box 1), whereas at a more caudal level, NCCs from the posterior mesencephalon and hindbrain, which is transiently subdivided into neuroepithelial segments called rhombomeres (r), colonize the PAs, another series of metameric structures ( Couly et al., 1996 Couly et al., 1993 Johnston, 1966 Köntges and Lumsden, 1996 Le Lievre, 1978 Le Lievre, 1974 Noden, 1983 Osumi-Yamashita et al., 1994) ( Fig. A full understanding of the underlying molecular mechanisms involved is central to advancing our understanding of craniofacial biology and evolution.Ĭranial NCCs follow stereotypical migratory pathways that are conserved among vertebrate species. Although the initial patterns of NCC segmentation and migration are mainly conserved between species, the wide diversity of vertebrate craniofacial morphologies indicates that cranial NCC subpopulations are able to generate distinctive, species-specific skeletal structures. Rostral cranial NCCs extensively contribute to the frontonasal skeleton and the membranous bones of the skull, whereas more posterior cranial NCCs fill the pharyngeal arches (PAs) (see Glossary, Box 1), where they form the jaw, middle ear, hyoid and thyroid cartilages ( Couly et al., 1993 Köntges and Lumsden, 1996 Noden, 1983) (for reviews, see Gross and Hanken, 2008 McBratney-Owen et al., 2008 Santagati and Rijli, 2003). Moreover, in the cranial region, NCCs contribute to most of the cartilage and bone of the skull, facial and pharyngeal skeletons. Following induction, NCCs delaminate and migrate to different regions of the embryo, where they differentiate into a broad range of cell types, including peripheral and enteric neurons, glia, melanocytes and smooth muscle ( Gammill and Bronner-Fraser, 2003 Le Douarin and Kalcheim, 1999 Morales et al., 2005 Steventon et al., 2005). The neural crest cells (NCCs) (see Glossary, Box 1) are a migratory cell population specific to vertebrates that originates from the dorsal part of the developing neural tube. ![]()
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