Developmental regulation of Ubc9 in the rat nervous system.

The SUMO-conjugating enzyme Ubc9 is an essential enzyme in the SUMO (small ubiquitin-related modifier) protein modification system. Although sumoylation, covalent modification of cellular proteins by SUMO, is considered to regulate various cellular processes, and many substrates for sumoylation have been identified recently, the regulation of Ubc9 expression has not been examined in detail. We analyzed the expression of Ubc9 during rat brain development at the mRNA and protein levels. Northern and Western blot analyses revealed that expression of Ubc9 and SUMO-1 was developmentally regulated, while that of the ubiquitin-conjugating enzyme UbcH7 did not change so dramatically. In situ hybridization analysis revealed that the expression of Ubc9 was high in neuronal stem cells and moderate in differentiated neurons at embryonic stages. In the adult brain, moderate expression was observed in subsets of neurons, such as the dentate granular neurons and pyramidal neurons in the hippocampal formation and the large pyramidal neurons in the cerebral cortex. These results suggest that the Ubc9-SUMO system might participate in the proliferation and differentiation of neuronal cells in the developing brain and in neuronal plasticity in the adult brain.