Abstract

Synaptic assembly is a critical step in the formation of functional neuronal circuits. Several signalling molecules have been identified as key players that modulate synapse formation. Extensive work has been done in elucidating how secreted signals act on their receptors to promote synaptogenesis. However, the mechanisms controlling the trafficking and location of surface receptors and their ability to signal to downstream targets remain poorly characterised. Our lab has been studying the role of Wnt signalling in synaptic connectivity in the vertebrate nervous system. We found that Wnt7a promotes the formation of synapses in the hippocampus. Presynaptically, Wnt7a requires Frizzled-5 (Fz5), a seven transmembrane receptor, to promote synapse formation. Importantly, loss of function of Fz5 blocks the response of neurons to Wnt7a to induce synapse formation. Moreover, we found that Wnts are required for activity-mediated trafficking of Fz5 to the cell surface. Importantly, we discovered a novel post-translational modification in Fz5 receptor that control its surface expression, its ability to activate the Wnt signalling cascade and to promote synapse formation. In this project, we will examine how this novel post-translational modification regulates Fz5 trafficking to the cell surface and its ability to activate the Wnt pathway. We will take a multidisciplinary approach that combines biochemical analyses, time-lapse imaging of fluorescently labeled receptors to visualize their trafficking, super-resolution microscopy to evaluate interactions with components of the Wnt signalosome, and in vivo analyses of receptor function during synapse formation. Our studies will shed new light into novel molecular mechanisms that control surface receptor levels and their ability to modulate downstream signalling. Our work will also have a impact in the field of embryonic development, cell biology and neuronal connectivity where the Wnt signalling pathway plays a key role.