Thesis #418

Activity-dependent plasticity in neurons involves changes in synaptic
transmission and connectivity. These changes lead to altered neuronal circuit
properties and are thought to underlie learning and memory. Transcription and
protein synthesis are indispensable in order to maintain changes in neural
circuitry over periods of several hours or longer. Therefore signaling from the
synapse to the nucleus is required to control activity-dependent expression of
RNA and proteins which have to be transported back to the activated synaptic
sites.
The small actin-binding protein profilin has been shown to accumulate in
postsynaptic dendritic spines of pyramidal neurons as a necessary element in
activity-dependent stabilization of synaptic morphology, a putative anatomical
correlate of changes in transmission strength. In this work I show that profilin also
enters the nucleus in an NMDA receptor and Ca2+ dependent manner. However,
in contrast to spine targeting, nuclear enrichment is reversible within minutes
after removal of the stimulus. Nuclear accumulation of profilin is likely coupled to
activity-dependent actin polymerization at the cell cortex which also takes place
in response to NMDA receptor stimulation.
Nuclear profilin has been implicated in different steps of gene expression
including transcription and pre-mRNA splicing. Activity-dependent nuclear and
synaptic accumulation suggests profilin to be involved in different aspects of
neuronal plasticity. To this end, I introduce approaches to elucidate profilin
function in experience-dependent plasticity and gene expression.