Our group is interested in the mechanisms and molecules that direct the formation of the vertebrate head. This is a complex issue, as it involves multiple interactions between a number of disparate embryonic cell types, and our long term aim is to characterise these interactions and define how they are co-ordinated to produce the adult head - to ascertain how the nerves, muscles and skeletal components of the head are laid down and organised into a functioning apparatus. This is an important area of research, which has ramifications outside the immediate field of developmental biology. There are numerous inherited conditions that result in malformations of the head, and thus our work will help in understanding the basis of many birth defects. Our work also informs us of the how the vertebrates evolved. The real difference between the vertebrates and our nearest relatives lie in the organisation of the head, and these difference are thought to have their basis in alterations to the programme that underlies the development of the head. Consequently, our work also feeds into our understanding of the evolutionary origin of the vertebrates. The development of the vertebrate head differs in a number of significant ways from the trunk, and one of the most glaring examples that has often been offered lies in the deployment of the neural crest. In the head, it is the neural crest cells that are the source of bone and cartilage, and furthermore, the cranial neural crest are thought to pattern the head. Our recent results however suggest that these views should be tempered. Recently, we have shown that trunk crest cells possess skeleotgenic capabilities. Thus neural crest from all axial levels can generate the full repetoire of crest derivatives, but during normal development the skeletogenic ability of the trunk crest is suppressed. However, this potential is noteworthy as it was likely realised in early vertebrates, which had extensive post-cranial exoskeletal coverings. Furthermore, we have also shown the development of the pharyngeal apparatus is a lot more consensual than was previously believed, and besides the important role played by the neural crest, it now apparent that the pharyngeal endoderm also plays a prominent part. Again, this is of evolutionary significance, as it is known that segmented pharyngeal endoderm preceded the neural crest during evolution. Indeed, a clear example of the integrative nature of the development of this region of the body can be found in our studies of the epibranchial placodes, which provide the sensory neurons that inervate the mouth and throat. We have shown that these placodes are induced to form by the pharyngeal endoderm, and then that the neurons, and their axons, produced by these structure are guided inwards by the neural crest to establish the sensory ganglia and their innervation of the brain.

The role of neural crest and neurogenic placodes in vertebrate head development.