Garner Lab Research Areas
Functional Assembly of CNS Synapses
Achieving a fundamental understanding of how cognition is encoded by the brain requires insights into the molecules that define synaptic junctions and their roles in regulating neurotransmission. Over the last two decades, we have devoted significant effort to identifying and characterizing proteins of vertebrate CNS synapses. Initial clues to the molecules that comprise synapses of different types came in the late eighties through a collaboration with Dr. Eckart Gundelfinger— currently a Professor at the Leibniz Institute for Neurobiology in Magdeburg, Germany. Our two groups first searched for proteins of the synaptic junction by screening cDNA expression libraries with polyclonal antibodies against rat brain synaptic junction. This led to the cloning of cDNAs of more than 80 novel synaptic proteins. Since that time, we have continued working together to evaluate the functional importance of many of these pre- and postsynaptic proteins, including Piccolo, Bassoon, SAP90, SAP97, SAP102, ProSAP, Jacob, and Brevican.
Using a combination of biochemical, cellular, molecular, electrophysiological and reverse genetic approaches, we have found that all of these proteins are scaffold proteins of primarily glutamatergic synapses. These proteins play fundamental roles in the nascent assembly and function of glutamatergic synapses. For example, members of the SAP90/SAP97 and SAP102 family of MAGUKs are involved in the transport, delivery, retention and activity of postsynaptic glutamate receptors. In contrast, the presynaptic active zone proteins Piccolo and Bassoon facilitate the assembly of the active zone and regulate the release of neurotransmitters.
More recently, it has become evident that members of the ProSAP/Shank families are linked to Autism Spectrum Disorders. Understanding how these molecules contribute to synaptic function will allow the development of rational research strategies to normalize function in individuals with autism.
Synaptic Protein Dynamics
As our studies of individual synaptic proteins progressed, we became increasingly interested in questions related to the dynamics of synapse formation. For example, how long does it take a nascent synapse to form? How are pre- and postsynaptic proteins delivered to nascent synapses? Once a synapse is formed, do the proteins that comprise the junction exchange and on what time scale (seconds, minutes, hours, days months or years)? How do these exchange kinetics relate to the life-time of individual synapses? What mechanisms regulate synapse stability and elimination?
To address these and related questions, we embarked on another collaboration with Dr. Noam Ziv of the Technion Institute in Haifa, Israel. Here we are using time-lapse confocal imaging of GFP-tagged synaptic proteins expressed in cultured hippocampal neurons to follow the time course of synapse formation and the exchange kinetics of proteins under different conditions. Our ongoing studies have shown that nascent synapses form in about an hour with the presynaptic active zone forming before the postsynaptic density (PSD) (Brelser et al., 2004). Furthermore, we have found that many of the pre- and postsynaptic proteins use vesicular intermediates for their delivery to nascent and mature synapses (Zhai et al., 2001; Shapira et al., 2003).
We have found that proteins within synapses are quite dynamic, exchanging on the order of 10s of minutes (Tsuriel et al., 2006). This is in stark contrast to the life of an individual synapse that can exist for many hours to days. Our future studies are designed to relate the dynamics of individual proteins to their proposed functions.
See also
The work described here was supported by grants from the National Institutes of Health, the Nancy Pritzker Foundation, the Hillblom Foundation, the Down syndrome research and treatment foundation (dsrtf.org), the Deutsche Forschungsgemeinschaft (DFG) and US-Israel Binational Science Foundation (BSF) .
