Systematic discovery of Olig2 upstream regulators for central nervous system myelination

Project Summary Myelination of the central nervous system (CNS) by oligodendrocytes (OLs) is essential for the function of the CNS. Genetic studies have shown that Olig2, a basic helix-loop-helix transcription factor, is a master regulator of OL lineage cells, playing an indispensable role in their specification from neural progenitors and their differentiation into myelin-forming OLs. Despite these central roles, little is known about how Olig2 expression is regulated in the OL lineage, representing a major gap in our understanding of CNS myelination. Simply put, the expression of a gene is regulated by upstream regulators acting on its enhancers (cis-regulatory DNA elements). To understand Olig2 expression, thus, one needs to identify its enhancers and transcription factors acting on them. Logically, enhancer identification would come first because, without the knowledge of enhancers, it would not be feasible to identify transcription factors acting on them. OL enhancers that govern Olig2 remained elusive in spite of a decade-long search. To make a breakthrough, we developed an innovative method that links enhancers to target genes in a principled manner. Using this method, we have identified a long-sought OL enhancer for Olig2, which was termed Olig2-E1. The discovery of Olig2-E1 opens the door to the systematic discovery of Olig2 upstream regulators. Since they likely exert their regulatory effects through Olig2-E1, one can find them by looking for transcription factors that alter the enhancer activity of Olig2-E1. Capitalizing on this powerful framework, we have identified Mef2d as a novel positive regulator of Olig2. Aim I will determine the role of Mef2d in Olig2 expression in vivo and OL myelination. Aim II will expand the search for novel Olig2 upstream regulators.