06-P011 A reevaluation of X-Irradiation induced phocomelia and proximodistal limb patterning

ro is the acquisition of protective barrier function in the skin a process involving differentiation of keratinocytes to form a stratum corneum of unique lipid composition and structure. Harlequin Ichthyosis (HI) is a severe hyperkeratotic skin disease caused by mutations in the ABCA12 transport protein and which results in profound barrier defects. In keratinocytes ABCA12 is thought to regulate the transfer of lipids into intracellular trafficking vesicles known as lamellar bodies although the exact role of the protein remains unclear. As part of an innovative mouse mutagenesis screen we have characterised an animal model of HI and showed that it displays many of the hallmarks of the disease. We have used this model to follow developmental disease progression and demonstrate that loss of Abca12 leads to premature differentiation of basal keratinocytes. Comprehensive analysis of mutant embryonic epidermis demonstrated profound defects in lipid homeostasis, illustrating the extent to which Abca12 plays pivotal roles in the developing skin. To further investigate the scope of Abca12’s activity, we utilised cells from the mutant mouse to ascribe direct transport functions to the protein and demonstrate activities independent of its role in lamellar body function. Furthermore, we identify Abca12 as a mediator of Abca1 regulated cellular cholesterol efflux, a finding which may have significant implications for other diseases of lipid metabolism and homeostasis, including atherosclerosis. Using grafts of embryonic epidermis we have begun to unravel the molecular changes which result from loss of Abca12 function.