Oligodendrocytes (OLs) are vital for nervous system function by myelinating axons in the central nervous system (CNS) to increase conduction velocity and provide metabolic support. The majority of OLs are generated by ventral pMN progenitors defined by the expression of the basic helix loop helix (bhlh) transcription factor Oligodendrocyte Transcription Factor 2 (Olig2), which give rise to motor neurons and OLs sequentially. OLs are initially specified as oligodendrocyte precursor cells (OPCs), which migrate through the spinal cord and then differentiate. However, not all OPCs become myelinating OLs. Instead, many remain as fate restricted proliferative progenitors through adulthood. Though 5-8% of the cells in the adult CNS are OPCs, the mechanisms that preserve this population are not well understood. As OPCs undergo differentiation, genes that promote cell cycle progression and progenitor identity are downregulated, while genes required for myelination and oligodendrocyte differentiation are upregulated. These changes in gene expression are orchestrated by stage-specific transcriptional activity of core oligodendrocyte lineage transcription factors such as Olig2. Olig2 can be a transcriptional repressor or activator depending on interactions with different co-factors. For example, Olig2 forms a complex with SWI/SNF Related, Matrix Associated, Actin Dependent (SMARCA4/ Brg1) to directly activate expression of myelin genes. Though Olig2 is expressed in all OL lineage cells, it is not well understood what regulates the transcriptional activity of Olig2 in OPCs. RNA-Seq data collected in the Appel lab found that PR/SET domain 8 (prdm8), a gene that encodes a transcriptional repressor, is expressed by OPCs but not oligodendrocytes. In the CNS, Prdm8 acts as a repressive co-factor with a close relative of Olig2, Basic Helix-Loop-Helix Domain Containing, Class B, 5 (Bhlhb5). Loss of function prdm8 zebrafish larvae have more oligodendrocytes and fewer OPCs, suggesting that Prdm8 inhibits oligodendrocyte differentiation. Using a combination of genetic manipulations, microscopy and biochemical methods in vivo, this proposal will address the possibility that Prdm8 forms a complex with Olig2 to maintain OPCs by repressing genes required for oligodendrocyte differentiation.
Aim 1 will test the sufficiency of Prdm8 to the inhibit oligodendrocyte fate and myelination.
Aim 2 addresses genetic targets of Prdm8 in the oligodendrocyte lineage.
Aim 3 will evaluate Prdm8 and Olig2 interactions. These investigations will advance the field of oligodendrocyte biology by providing a deeper understanding of transcriptional regulation that preserves OPCs.
Aberrant oligodendrocyte development and myelination is observed in many neurological disorders ranging from Multiple Sclerosis to Autism that result in motor and cognitive dysfunction. A deeper comprehension of the molecular mechanisms that regulate oligodendrocyte development are required to understand the etiology of these disorders and to develop therapeutics that promote myelin repair. The proposed research will uncover transcriptional mechanisms that inhibit oligodendrocyte differentiation and myelination.
