A network of genes is recruited in developing oligodendrocytes to coordinate the production of myelin, a deficiency of which can drastically impair neuronal function in the central nervous system. Mechanisms operative in regulating myelin gene expression can be revealed by defining the set of transcription factors and signaling pathways that are selectively and temporally activated in developing oligodendrocytes. To examine the changing pattern of transcription factors and other genes selectively expressed by developing oligodendrocytes, we established a reliable microarray system combined with purification of oligodendrocytes by flow cytometry at different stages of differentiation (Nielsen et al., 2006). Such an approach has enabled the isolation and profiling of a novel, non-myelinating population of oligodendrocytes. The function and regulation of several genes expressed by this population of non-myelinating oligodendrocytes is being further examined in transgenic models to identify the molecular basis for the switch from a non-myelinating to a myelinating phenotype. In addition to profiling messenger RNAs (mRNAs) with microarray technology, we examined microRNAs (miRNAs), a class of small non-coding RNAs with a roles in post-transcriptional regulation. We are defining those miRNA candidates that may regulate oligodendrocyte specification, proliferation and differentiation by conferring an additional level of selectivity to the gene expression program (Lau et al., in press). Of the genes that are dynamically regulated during oligodendrocyte development, we selected several novel proteins for functional characterization (Nielsen et al., 2006). Together with this discovery-driven approach to identifying genes relevant for oligodendrocyte development, we continued our long-term study on the mechanism by which the zinc finger transcription factor Myt1 regulates neural gene transcription. Myt1 was found to interact with a transcriptional co-repressor, Sin3, that may locally modify chromatin structure to regulate myelin gene transcription (Romm et al., 2005). Finally, combining transcriptomics with in vivo demyelinating paradigms, we evaluated the expression profile following myelin loss (Lovas et al., submitted). These studies form the basis for devising strategies to promote remyelination in diseases such as multiple sclerosis, Pelizaeus-Merzbacher disease and spinal cord injury by stimulating endogenous oligodendrocyte progenitors to proliferate, migrate and myelinate.