Helene Cousin

During development, extensive cell movements change the shape the embryo from a sphere with a radial symmetry to an elongated, multilayered and asymmetric organism. The first morphogenetic movement occurs at gastrulation, when the mesoderm (that gives rise to the muscles, heart and blood vessels) and the endoderm (that gives rise to the gut, liver, pancreas etc…) are internalized. During neurulation, the neural tissue “rolls up” into a tube and the somitic mesoderm (future muscles) undergoes segmentation and rotation. After neurulation is complete, the dorsal most cells called neural crest cells undergo extensive migrations in the embryos and give rise to the melanocytes, and ganglia in the trunk and to most of the facial structures in the head. The Cranial Neural Crest (CNC) originate from the dorsal tube of the brain and migrate along define pathways (mandibular, hoid and branchial) and will coordinate the entire development of the face. They will eventually differentiate into many structures including the majority of the craniofacial bones, cranial nerves, glial cells and teeth. The CNC is one of the most plastic cell populations in the animal kingdom, capable of differentiating into structures of variable shape depending on the species, allowing them to adapt themselves to their feeding habits. For example, the jaw and nasal region of birds forms the beak capable of breaking hardest seeds (Toucan and parrots) or capable of reaching down the long nectar tubes of flowers (humming birds), while in elephants, it forms an elongated and flexible trunk. The plasticity of the CNC is also evident in the variety of birth defects associated with it, which result from improper migration, survival or differentiation of the CNC (Cleft palate, Treacher Collins syndrome, CHARGE syndrome etc…). What drives this plasticity? Can we manipulate it so prevent or correct craniofacial defects?