Knock-down of the Golli Myelin Basic Protein in M3 Enhancer Knock-out Mice Causes the Dysregulation of Embryonic Stem Cell Differentiation

During development, in the central nervous system (CNS), oligodendrocyte progenitor cells (OPCs) migrate to axons and eventually become mature oligodendrocytes. Mature oligodendrocytes wrap around axons and produce myelin sheaths, which insulate the axons. Growth factors, specifically platelet derived growth factor (PDGF) and fibroblast growth factor (FGF), are released in the development of OPCs to promote congruent gene expression. PDGF is released to induce the proliferation of OPCs, and to promote their migration to axons. FGF induces OPC maturation into oligodendrocytes, and initiates axon myelination. OPCs act in a similar fashion following a spinal cord injury. PDGF and FGF are released as new OPCs develop, migrate to the injury site, and mature into oligodendrocytes in an attempt to repair damaged axons. We observed the same processes occurring in vitro with embryonic stem cells (ESCs) from our wild-type mouse model. Growth factors FGF and PDGF were added to the media to promote OPC morphology in mature ESCs by the activation of their respective growth factor receptors leading to the phospholipase C-gamma (PLCγ) pathway which results in the Ca 2+ efflux from the endoplasmic reticulum (ER). In 1993, the Campagnoni lab discovered that the myelin basic protein (mbp) gene was part of a larger transcription complex called golli-mbp, whose products regulate store operated calcium channels on the ER membrane. We were able to better study the effects of golli-MBP through our M3 enhancer knockout (M3KO) mouse model where golli-MBP products were downregulated at the OPC stage of development. Deletion of the M3 enhancer resulted in the down regulation of both golli and MBP specific proteins in vivo. We generated WT and M3KO ES cell lines to investigate the potential influence of Golli-MBP in progenitor cell maturation. We found that the M3KO ES cells did not respond to FGF or PDGF to allow for proper cell adhesion and the differentiation into OPCs. These results suggest that deletion of the M3 enhancer reduces the expression of golli-MBP, which leads to the dysregulation of the signaling pathways necessary for the differentiation of ES cells into OPCs.