My laboratory is
interested in the molecular changes that occur at synapses in
response to experience. We have focused on proteins associated
(either directly or as downstream targets) with the NMDA subtype
of glutamate receptor, an important mediator of many forms of
synaptic plasticity and learning in mammals. We utilize a
combination of approaches ranging from molecular biology and
biochemistry to cell biology, imaging, and mouse genetics to
address the following aspects of synaptic modification.
spine size, motility, and morphology
Spines are small, actin-rich dendritic protrusions that form the
sites of excitatory synaptic input in the mammalian CNS. Spines
uniquely exhibit morphological rearrangement in response to
activity and therefore have been proposed to represent
structural correlates of long-term information storage. We have
identified a key actin regulatory protein, SPAR, which
associates with NMDA receptors and promotes dramatic enlargement
of dendritic spines. We are currently testing the hypothesis
that SPAR is required for activity-dependent growth of spines,
and that this augmentation is important for memory formation or
stabilization in vivo.
Regulation of synapse number
Because strength of synaptic transmission is intimately related
to the density of synapses on a neuron, synaptogenesis and
synapse loss are both expected to play important roles in
controlling activity levels. We are studying an
activity-inducible serine-threonine kinase of the polo family,
SNK, which triggers synapse elimination via the phosphorylation
and ubiquitin-mediated degradation of key postsynaptic proteins,
including SPAR. We are generating mutants in SNK to determine
the involvement of this kinase in various paradigms of synapse
turnover: during neurodevelopment (e.g. â€œpruningâ€?), learning
(information editing), and in neurodegenerative disorders that
are often characterized by excessive synapse loss.
targeting of signaling enzymes
is well established that protein kinases including protein
kinase C (PKC) and cAMP-dependent protein kinase (PKA) play
critical roles in NMDA receptor-dependent synaptic plasticity.
However, the organization of these signaling microdomains
remains unclear, particularly at glutamatergic synapses. Using
yeast two-hybrid and biochemical approaches we are undertaking
the identification of novel scaffolding and targeting
infrastuctures for PKC and cAMP metabolic/responsive enzymes
situated in molecular proximity to the NMDA receptor.
Activity-dependent changes in synaptic protein composition
long-term interest of the lab is to understand at the proteomic
level how synaptic stimulation alters synapse content.
Following chemical bath applications to mimic particular
patterns of synaptic activity, we are using combined biochemical
purification of postsynaptic densities and microarray analysis
to characterize two aspects of synaptic plasticity: the ensemble
of proteins that rapidly translocates into synapses and may
contribute to short-term plasticity, as well as the de novo gene
expression that occurs on a longer timecourse that contributes
to long-lasting synaptic modifications.