Neural crest cells provide species-specific patterning information in the developing branchial skeleton

The skeletal elements of the branchial region are made by neural crest cells, following tissue interactions with the pharyngeal endoderm. Previous transplantation experiments have claimed that the cranial neural crest is morphogenetically prespecified in respect of its branchial skeletal derivatives, that is, that information for the number, size, shape, and position of its individual elements is already determined in these cells when they are still in the neural folds. This positional information would somehow be preserved during delamination from the neural tube and migration into the branchial arches, before being read out as a spatial pattern of chondrogenesis and osteogenesis. However, it now appears that signals from the endoderm are able to specify not only the histogenic differentiation state of neural crest cells but also the identity and orientation of the branchial skeletal elements. It is therefore important to ask whether fine details of branchial skeletal pattern such as those that exist between different species are also governed by extrinsic factors, such as the endoderm, or by the neural crest itself. We have grafted neural crest between duck and quail embryos and show that the shape and size of the resulting skeletal elements is donor derived. The ability to form species-specific patterns of craniofacial skeletal tissue thus appears to be an inherent property of the neural crest, expressed as species-specific responses to endodermal signals.