STEM-05. THE CONSERVED TUMOR SUPPRESSOR LGL1 REGULATES ADULT OLIGODENDROCYTE PROGENITOR CELL DIVISION MODE AND PREVENTS PREMALIGNANT PHENOTYPES

Mammalian oligodendrocyte progenitor cells (OPC) divide asymmetrically by dispatching pro-mitotic NG2, EGFR and PDGFRalpha, from here on called the NG2 complex, unequally between daughter cells to establish a cell fate bias and to restrict proliferation. Studies in genetically engineered mouse models have shown that OPC are a putative cellular origin of glioma and have furthermore suggested that asymmetric divisions are tumor suppressive and can be exploited therapeutically. The objective of this project is to test directly if disruption of asymmetric divisions causes premalignant phenotypes and even neoplastic transformation. To reach this objective, we study the hypothesisthat a mammalian gene called Lethal giant Larvae, Lgl1 regulates asymmetric OPC divisions. Lgl1 is frequently inactivated and its expression is lost in glioma. We propose that genetically enforced deletion of Lgl1 will disrupt asymmetric divisions and lead to premalignant changes and perhaps neoplastic transformation. We use a novel FACS based approach to determine if Lethal giant larvae1 (Lgl1) is expressed in OPC. We genetically enforce deletion of Lgl1 in OPC either conventionally with NG2-Cre or conditionally by injecting tamoxifen into triple transgenic mice obtained by breeding Lgl1fl/fl NG2CreERT2 and fluorescence reporter mice. Cre-conditional deleted Lgl1 OPC were analyzed in situ for changes in cell division mode, proliferation rate and differentiation. Whole genome expression analyses were conducted on ex vivo isolated Lgl1 knockout OPC. Lgl1 deletion in embryos leads to tumor formation albeit at low frequency and with long latency. Cre-conditional Lgl1 knockout in adult OPC increases symmetric division and proliferative rate at the expense of asymmetric divisions and differentiation. Whole transcriptome analyses reveal that Lgl1 regulates receptor-mediated endocytosis. Lgl1 loss fails to route NG2 complex to the lysosome for degradation, thereby rapidly increasing NG2 complex levels at the cell membrane and leading to symmetric OPC divisions and immediate premalignant changes such as hyperproliferation.