Oligodendrocytes are myelinating glial cells found in all regions of the central nervous system. The major function of oligodendrocytes is to form myelin sheaths around axons to ensure the rapid and faithful transmission of electrical signals. During development, oligodendrocytes precursor cells (OPCs) have to go through a series of morphological and molecular changes before they become fully differentiated into mature myelinating oligodendrocytes. The differentiation and myelination processes of oligodendrocytes are tightly controlled by transcription factors. Recent studies have demonstrated that Sox10 transcription factor directly stimulates OPC differentiation and myelin gene expression. However, OPC differentiation is tightly regulated by other transcription factors (TFs) including Nkx2.2, Olig1, Hes5 and Id4, all of which are expressed in undifferentiated OPC cells in the developing central nervous system. While Nkx2.2 and Olig1 function to promote OPC differentiation, Hes5 and Id4 act as inhibitors of OPC maturation. The functional relationship of these four regulatory TFs in the control of OL differentiation has not been determined. In this application, we hypothesize that Nkx2.2 enhances OPC maturation indirectly by suppressing the expression or function of Hes5 and Id4, but functions synergistically with Olig1 in promoting OPC differentiation. These hypotheses will be tested in the first two aims of the proposal. Recent data showed that Nkx2.2 is rapidly down-regulated in differentiated OLs and over-expression of Nkx2.2 in oligodendrocyte cell line inhibits MBP gene expression, raising the possibility that Nkx2.2 switches its role to become a repressor of myelin gene expression in mature OLs to prevent excessive myelin production. This possibility will be examined in the third aim of the proposal. Finally, we will test the hypothesis that persistent expression of Sox10 in mature OLs functions to maintain myelin gene expression and myelin sheath stability. The interplay of Sox10 and Nkx2.2 in myelinating OL cells may be responsible for the delicate balance of myelin production and structural maintenance. This line of study could help us understand molecular pathways that control axonal myelination process and provide insights into the development of molecular approaches to stimulate oligodendrocyte regeneration and remyelination in demyelinating diseases.
The proposed studies will provide important information on the function and regulations of transcription factors that control oligodendrocyte differentiation and myelin gene expression in the developing central nervous system. Knowledge obtained from this study can help us understand the molecular pathways that govern the differentiation and myelination of oligodendrocytes, and provide cues for promoting oligodendrocyte regeneration and axonal remyelination in neurological patients and spinal cord injury patients.
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