Patterning of the hyoid cartilage depends upon signals arising from the ventral foregut endoderm

Abstract

Hyoid bone is a part of the visceral skeleton which arises from both Hox-expressing (Hox؉) and Hox-nonexpressing (Hox-) cephalic neural crest cells. In a previous work, we have demonstrated that the Hox-neural crest domain behaves as a naïve entity to which the ventral foregut endoderm confers patterning cues to specify the shape and orientation of the nasal and mandibular skeleton. By using ablation and grafting approaches, we have extended our study to the formation of the hyoid bone and tested the patterning ability of more caudal levels of the lateroventral foregut endoderm in the chick embryo at the early neurula stage. In this study, endodermal stripes have first been delineated according to the projection of mid-and posterior rhombencephalic structures. The extirpation of endodermal transverse stripes along the anteroposterior axis selectively hampers the formation of the ceratobranchials and epibranchials. Thus defined, the patterning ability of the endodermal stripes was further explored in their medial and lateral parts. When homotopically engrafted on the migration pathway of cephalic neural crest cells, ventromedial zones of endoderm lead to the formation of supernumerary basihyal and basibranchial, while lateral zones generate additional cartilaginous pieces recognizable as ceratobranchial and epibranchial. Taken together, our data demonstrate that, early in development, the ventral foregut endoderm exerts a regionalized patterning activity on the cephalic neural crest to build up the primary facial and visceral skeleton in jaws and neck and enable a map of the endodermal skeletogenic areas to be drawn. This map reveals that a cryptic metamerization of the anterior foregut endoderm precedes the formation of the branchial arches. Developmental Dynamics 228: 239 -246, 2003.

Recent advances in craniofacial morphogenesis

“…During the development of the first branchial arch, pharyngeal endoderm is thought to prepattern the orofacial epithelium, which in turn will provide instructive signals to pattern the CNC-derived mesenchyme (Haworth et al, 2004). In zebrafish studies, fibroblast growth factor (FGF) signaling has been shown to be critical for the development of pharyngeal endoderm itself and for the mediation of the endoderm to regulate facial skeletal morphogenesis (Ruhin et al, 2003;Crump et al, 2004;Helms et al, 2005). On the other hand, a recent study has shown that pharyngeal endoderm is not critical for the normal development of the upper and lower face.…”

Spatio‐temporal dynamics of gene expression of the Edn1‐Dlx5/6 pathway during development of the lower jaw

“…Whereas CNCCs give rise to most chondrocranial and dermatocranial elements of the jaws (Clouthier et al, 1998;Couly et al, 2002;Depew and Simpson, 2006;Kontges and Lumsden, 1996;Ruhin et al, 2003), they do not possess, before migration, the topographic information needed to carry out the jaw morphogenesis (Couly et al, 1993). Surgical removal and grafting of small territories of the foregut endoderm at different developmental stages has shown that this epithelium provides to CNCCs part of the topographic information needed to form jaw structures (Couly et al, 1993;Kontges and Lumsden, 1996;Kurihara et al, 1994;Le Douarin and Dupin, 2003;Noden and Trainor, 2005;Trainor and Tam, 1995).…”

Retinoic acid is required for endodermal pouch morphogenesis and not for pharyngeal endoderm specification

“…It was believed that the pharyngeal arches obtain their identity from neural crest cells that migrate in segmental streams from the hindbrain into the arches . However, several recent studies have shown that the pharyngeal endoderm plays a much more important role in pharyngeal arch development than previously anticipated (Veitch et al, 1999;Piotrowski and Nusslein-Volhard, 2000) and patterns neural crest cells along the anteriorposterior (a/p) axis (Couly et al, 2002;Ruhin et al, 2003). Studies of zebrafish mutants, Xenopus, and knockout mice have significantly contributed to our understanding of how the endodermal germ layer is initially formed (Alexander and Stainier, 1999;Gritsman et al, 1999;Yasuo and Lemaire, 1999).…”