Polarity complexes in cellular differentiation

My NSERC Discovery program has focused on identifying protein-protein complexes that regulate cell polarity. In particular we have been focusing on the role of these complexes play in the development of the synapse, one of the more polarized structures in the CNS. Synapses are sites of cell-cell contact specialized for the transmission of chemical and electrical signals between neurons. The specialized function of the synapse results from the asymmetric distribution of proteins forming the presynaptic and postsynaptic compartments, and involves the coordinated regulation of actin dynamics. Not surprisingly then, signalling pathways that regulate the activity of the small Rho GTPases, Rac, Rho and cdc42, have been shown to play an important role in the development and maintenance of the synapse and synaptic morphology.

Work from our group has shown that a known polarity protein, Scribble, associates with the adaptor protein nitric oxide synthase adaptor protein (NOS1AP) through a unique protein-protein interaction. This interaction controls synaptic morphology by affecting the activated state of the small RhoGTPase protein, Rac1. To further characterize the role of NOS1AP in the synapse, we conducted a mass spectrometry screen and identified an interaction with N-Cadherin and other proteins implicated in endocytosis. In addition to NOS1AP, we identified that the scaffolding protein, Angiomotin (AMOT), associates with known polarity proteins. We have characterized a role for AMOT and the Lats1 kinase in regulating synaptic morphology. We continue to build on our NSERC program studying the role for known polarity proteins in the synapse. In this granting period we propose to:

i)Characterize a role for NOS1AP in N-cadherin stability in synaptic membranes. In an attempt to further define a role for NOS1AP in the synapse, we conducted a proteomic screen and have now linked NOS1AP with N-cadherin and proteins implicated in the endocytosis of receptor complexes. We will characterize the molecular nature of this NOS1AP complex and determine how this complex regulates the endocytosis of N-Cadherin to affect dendritic spine morphology.

ii) Characterize a role for Hippo dependent kinase in synaptic morphology. Our previous work has revealed the importance of AMOT in stabilizing actin in dendritic spines, and the importance of the core Hippo kinase Lats1 in this process. We will extend this work to examine the effects of other core Hippo kinases in this process, and whether neuronal activity affects the activity of these core Hippo kinases to then affect dendritic spine morphology.

Together, this program will contribute to our understanding of how known polarity proteins and polarity complexes regulate synaptic morphology and development, and further our understanding of the importance of the evolutionary conserved Hippo pathway in regulating synaptic morphology.