Final Activity Report Summary - PCP MAMMALS (Functional charaterization of Vangl2 interactions) The general aim of our research is to investigate the molecular basis of planar polarity in mammals. The planar cell polarity (PCP) signalling pathway was first identified in the fruit fly Drosophila, where it controls the uniform orientation of hairs and bristles on the body. More recently, complementary studies in mice and other animal models have demonstrated how this signalling pathway may be directly relevant to human biology and pathologies. Mutations in PCP genes have been linked, directly or indirectly, to pathologies in the central nervous system (neural tube defect, mental retardation), the sensory systems (hearing, balance, vision) the tissue homeostasis (polycystic kidney disease), or even cardiac malformation, and probably more are to be identified. In this project, we focus on Van Gogh like-2 (Vangl2) that we believe is a core molecule controlling many aspects of planar polarity cascades in mammals. More specifically we wanted: 1-To identify some molecular networks associated to Vangl2. 2-To identify new interacting partners for Vangl2 in mammals. The first part of that project was focussed on rac1, a small GTPase, that has the ability to modify dramatically the actin cytoskeleton, and seemed like a good candidate to translate some of the information from Vangl2 to the cytoskeleton. Our data show a specific pattern of expression of rac1 in the cochlear epithelium of mammals, and that the disruption of rac1 cascade leads to dramatic impact on the hair bundle integrity. Our data also show a link between the levels of activated rac1 and vangl2 normal expression. A similar link was found for JNK, a kinase that is believed to act downstream of rac1. These data suggest the existence of a Vangl2/rac1/JNK cascade in mammalian ear: that could participate in the establishment of planar polarity in hair cells, but probably in a more general control of polarity and maturation. We are in the process of making mutants for rac1: that will greatly help us understand the exact impact of rac1 on hair bundle PCP and morphology. The second part of the project was to identify new interactors for Vangl2. Using yeast-2-hybrid techniques, we were able to isolated hundreds of potential partners that we are still in the process of identifying. We did pick of them, a molecule called GIPC1, for further analysis. Our data confirmed the specific interaction of Vangl2 and GIPC1, and suggest that GIPC1 participate in Vangl2 trafficking within the cell, and in hair bundle morphology. We hypothesized that GIPC1 could participate in the maintenance or establishment of Vangl2 asymmetry within hair cells. We still have many potential partners to study, and we also started another approach to find partners for Vangl2, in collaboration with a group in Marseille (Andre le Bivic), through mass spectrometry. The outcome of this project is a better understanding of the mechanisms involved in planar polarity in mammals, which has a strong potential to lead to the development of novel therapeutic targets for numerous neuronal and sensory diseases.