BACKGROUND: Small Ubiquitin-like MOdifier protein (SUMO) is a key regulator of 
nuclear functions but little is known regarding the role of the 
post-translational modification sumoylation outside of the nucleus, particularly 
in the Central Nervous System (CNS).
METHODOLOGY/PRINCIPAL FINDINGS: Here, we report that the expression levels of 
SUMO-modified substrates as well as the components of the sumoylation machinery 
are temporally and spatially regulated in the developing rat brain. 
Interestingly, while the overall sumoylation is decreasing during brain 
development, there are progressively more SUMO substrates localized at synapses. 
This increase is correlated with a differential redistribution of the 
sumoylation machinery into dendritic spines during neuronal maturation.
CONCLUSIONS/SIGNIFICANCE: Overall, our data clearly demonstrate that the 
sumoylation process is developmentally regulated in the brain with high levels 
of nuclear sumoylation early in the development suggesting a role for this 
post-translational modification during the synaptogenesis period and a 
redistribution of the SUMO system towards dendritic spines at a later 
developmental stage to modulate synaptic protein function.