03-P024 Dual splice variants of autotaxin control chicken diencephalon–mesencephalon development downstream of Pax6

Abstract

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.Gsk-3b is a constitutively active protein kinase which has regionalized expression in the developing face and skull.Phosphorylation of b-catenin by GSK-3b leads to proteasomal degradation and dampening of Wnt signaling. GSK-3b also regulates hedgehog (Hh) signaling, by converting GliA to GliR forms. GSK-3b null animals have a cleft palate and delayed skull osteogenesis. The craniofacial phenotypes in the GSK-3b null animals may be attributed to distinct roles in Wnt and Hh signaling. We hypothesize that changes in Wnt signaling are responsible for the skull ossification defects while the palatal defects may be Hh derived. We are using genetic approaches to test these hypotheses. We are utilizing the Axin2 mutation to manipulate the Wnt/ b-catenin pathway in GSK-3b-null animals. Our preliminary data suggests that GSK-3b and Axin2 synergize during ossification of the skull. In addition, we are exploring genetic interactions between GSK-3b and the Hh pathway members, Patched1, and Gli3. Here, we will present genetic evidence for GSK-3b regulation of both Hh and Wnt signaling in the development of the skull.Autotaxin (ATX) is a secreted, phospholipid-generating enzyme originally identified as a motility-promoting factor in a human melanoma cell line. We previously reported that chicken ATX is expressed in the developing diencephalon; however, its role has not been elucidated. To determine the role of ATX in chicken brain dev...