Analyzing Time of Chromosomal Rearrangment in Glioblastoma

Glioblastoma is the most common and aggressive type of malignant brain tumor. Due to the tumor cell’s ability to disperse through- out the brain, their resistance to traditional chemotherapy and high rate of tumor relapse, current research is focusing on determining and designing therapies against the tumor cell-of-origin. In order to determine the cell of origin in these tumors, labeled mutant cells were generated through the use of mosaic analysis with double markers (MADM) allowing our lab to track the entire tumorigenic process in vivo and determine which cell types were giving rise to tumors. It was found that oligodendrocyte precursor cells (OPCs) were the primary cell type to show overexpansion and eventually give rise to a malignant tumor. It was hypothesized that by ablating the OPC cell population, using a genetic tool, one could prevent tumor formation or slow tumor growth. OPC specific thymidine kinase (TK) in conjunction with the drug Ganciclovir (GCV) was used in the hopes of causing OPC death. However, when end stage tumors were analyzed it was found that TK expression had been lost within the tumor cells, but not mutant OPCs outside of the tumor region. DNA analysis showed that the loss of the TK transgene had occurred on a genomic level, suggesting that a region of genomic DNA had been lost. The goal of this study is to characterize when the loss of TK occurs. Analysis of small tumors will reveal if TK loss is necessary for tumor growth or if it is lost as a function of tumor growth.