Spatial relations between avian craniofacial neural crest and paraxial mesoderm cells

Abstract

Fate maps based on quail-chick grafting of avian cephalic neural crest precursors and paraxial mesoderm cells have identified the majority of derivatives from each population but have not unequivocally resolved the precise locations of and population dynamics at the interface between them. The relation between these two mesenchymal tissues is especially critical for the development of skeletal muscles, because crest cells play an essential role in their differentiation and subsequent spatial organization. It is not known whether myogenic mesoderm and skeletogenic neural crest cells establish permanent relations while en route to their final destinations, or later at the sites where musculoskeletal morphogenesis is completed. We applied ␤-galactosidase-encoding, replication-incompetent retroviruses to paraxial mesoderm, to crest progenitors, or at the interface between mesodermal and overlying neural crest as both were en route to branchial or periocular regions in chick embryos. With respect to skeletal structures, the results identify the avian neural crest:mesoderm boundary at the junction of the supraorbital and calvarial regions of the frontal bone, lateral to the hypophyseal foramen, and rostral to laryngeal cartilages.

The differentiation and morphogenesis of craniofacial muscles

“…6, 7; see also Fig. 10;Wahl et al, 1994;Evans and Noden, 2006). These studies identified progenitors for endothelial cells, smooth muscles, and a wide range of connective tissues in addition to skeletal muscles within paraxial mesoderm.…”

“…However, other researchers have been unable to visualize somitomeres (Wachtler and Jacob, 1986) and, thus far, no molecular evidence of a segmental organization within this mesoderm has been found (Freund et al, 1996). Moreover, the initial sites of specific muscle, cartilage, and bone determination do not correspond to individual somitomeres (Noden, 1983b;Couly et al, 1992;Evans and Noden, 2006). Comparative analyses show that the position of specific somitomeres relative to other axial structures, specifically mid-and hindbrain segments, is not constant among embryos of the different vertebrate classes thus far examined.…”

“…5) and eliminates any observable spatial distinction between them. Transplantation and retroviral mapping (Evans and Noden, 2006) studies show that these cells contribute to the formation of the dorsal, ventral, and medial rectus and ventral oblique muscles, all of which are innervated by the oculomotor (IIIrd) nerve. Whether prechordal cells are the exclusive source of myoblasts for these EOMs or share this fate with paraxial mesodermal populations is unresolved.…”

“…With the availability of progenitor cell-labeling methods, especially in avian (Noden, 1983b;Couly et al, 1992Couly et al, , 1993Evans and Noden, 2006) and murine embryos (Trainor and Tam, 1995;Gage et al, 2005), it was discovered that all head myoblasts arise in paraxial mesoderm, often far removed from the locations at which overt condensation and terminal differentiation will occur (Fig. 7).…”

Tbx1 regulation of myogenic differentiation in the limb and cranial mesoderm

“…This analysis revealed that Tbx1 transcripts are clearly apparent in the mesoderm adjacent to the caudal hindbrain from stage 7, encompassing the region that will give rise to the first and second arch muscles and the lateral rectus muscle (Fig. 3A, black arrow and data not shown; Evans and Noden, 2006; reviewed by Noden and Francis-West, 2006). In contrast, capsulin expression was undetectable in the cranial mesoderm ( Fig.…”