Research groups

Figure 1. Mutant PICK1 that cannot bind or inhibit Arp2/3-mediated actin polymerisation blocks NMDA-induced AMPAR internalisation. Cultured hippocampal neurons were transfected with WTPICK1-IRES-GFP or mutantPICK1-IRES-GFP and NMDA-induced internalisation was analysed by antibody-feeding immunocytochemistry. Internalised and surface GluR2 were visualised using different coloured secondary antibodies.

Learning and memory involves changes in the molecular machinery of synapses. AMPA receptors (AMPARs) mediate the majority of fast excitatory synaptic transmission in the brain, and plasticity at excitatory synapses involves alterations in the number of AMPARs localised at the synaptic plasma membrane, brought about by regulated receptor trafficking.

AMPAR expression at the synaptic plasma membrane is regulated by endocytosis, exocytosis, recycling and lateral diffusion events that contribute to reductions (Long Term Depression, LTD) or increases (Long Term Potentiation, LTP) in synaptic strength. A number of proteins interact with AMPAR subunits and tightly regulate these trafficking events.

The main focus of my lab is investigating how these interacting proteins influence basic cell biological processes to bring about changes in AMPAR trafficking and hence synaptic strength. In particular, we are studying a protein called PICK1, which binds GluR2/3 subunits of AMPARs, and is involved in AMPAR internalisation and LTD.

One of the current projects in the lab is investigating the functional interaction between PICK1 and the machinery that regulates actin polymerisation. We recently showed that PICK1 inhibits Arp2/3-mediated actin polymerisation, and that this is required for NMDA-stimulated AMPAR internalisation and LTD (Rocca et al., 2008; see figure 1). We are now studying the upstream signaling pathways that modulate this inhibition.

Figure 2. Cultured hippocampal neuron transfected with GFP-Actin, which is concentrated in dendritic spines. The zoomed section demonstrates how spines can be readily visualised using this technique.

In another project, we are studying AMPAR trafficking events that occur in an in vitro model of ischaemia (stroke). We believe that these trafficking events have certain features in common with LTD/LTP, and we have recently demonstrated that PICK1 regulates GluR2 trafficking during oxygen/glucose deprivation of hippocampal neurons (Dixon et al., 2009).

In addition to AMPAR number, synaptic strength correlates with the size of dendritic spines, which are the tiny protrusions on the dendrites of neurons that house the postsynaptic specialisation. They act to compartmentalise both the machinery and the biochemical signals that underlie synaptic transmission, providing a mechanism to ensure synapse-specificity for transmission and plasticity (see figure 2).

We are studying the molecular mechanisms that underlie changes in spine size during synaptic plasticity, and we are interested in how regulation of AMPAR trafficking may be linked to the regulation of spine morphology.