03-P022 Orbiting the eye: An analysis of scleral cartilage development

Orbital cartilage encircles the eye giving strength and support to the neural retina. It is derived from cranial neural crest cells (NCCs), cells that can generate a number of cell types including neurons, glia, and melanocytes. Uniquely in the head, NCCs also make skeletal derivatives that form the majority of the craniofacial skeleton. Differentiation of NCCs into cartilage requires inductive interactions between NCCs and the local environment. The nature of these interactions is largely unknown. We hypothesise that formation of the eye socket requires interactions between the eye and the NCCs during early development. This is supported by evidence in animals and humans where lack of eyes (anophthalmia) or formation of small eyes (microphthalmia) result in craniofacial abnormalities. Orbital cartilage is found in the majority of vertebrates but the ability to induce it has been lost to mammals. A comparison of chick and mouse should help us determine which tissues and molecules are necessary for this cartilage to form. We have examined the gene expression patterns of cartilage markers and the definitive cartilage stain Alcian Blue, to show the development of orbital cartilage in the chicken embryo, in addition to showing the initiation of cartilage formation in the mouse. We demonstrate cartilage formation is halted in chick following early eye removal and the neural ectoderm derived-retinal pigment epithelium can induce ectopic cartilage to form in cranial NCCs. Ligand and receptor gene expression patterns indicate a role for Fgfs in the development of this tissue. Funded by the Wellcome Trust.