Identification of numerous genes differentially expressed in rat brain during postnatal development by suppression subtractive hybridization and expression analysis of the novel rat gene rMMS2

During postnatal development the potential for axonal growth and regeneration in the central nervous system (CNS) becomes very restricted. This decline of axon growth and regeneration might be due to developmental alterations in the expression level of genes which are strongly expressed in differentiating neurons during formation of axons, but which are downregulated later in development. In order to identify genes which are downregulated in rat brain with the completion of neuronal differentiation, we performed suppression subtractive hybridization (SSH) with rat cerebellum at two developmental stages. Several differentially expressed genes were identified. We present the detailed expression analysis of one of these, rMMS2, which is the rat homologue of mouse ubiquitin-conjugating enzyme-like protein MMS2 and belongs to a family of ubiquitin-conjugating enzyme variants (UEVs) that are highly similar to ubiquitin-conjugating enzymes E2 (Ubcs) but lack the essential amino acid residue in the active site. UEVs play a role in DNA repair and are possibly involved in ubiquitination, which may be important for the assembly and function of neuronal circuits. In the present study, we examined the temporal and spatial expression of rMMS2 transcript and show a strong developmental downregulation in rat brain by Northern blot analysis and in situ hybridization. The mRNA of rMMS2 is widely distributed in rat brain at late embryonic development but is differentially regulated during postnatal development; its expression is strongly reduced during maturation of the CNS. Our results show that SSH is a suitable method for identifying genes which are regulated during postnatal development and suggest that the newly identified rat UEV rMMS2 may play a role in neuronal development and differentiation.