BIOL-11. THE ROLE OF ABERRANT EXPRESSION OF PRDM6 IN THE DEVELOPING CEREBELLUM AND IN GROUP 4 MEDULLOBLASTOMA

Group 4 medulloblastoma is the most common medulloblastoma subgroup with an intermediate prognosis and a high incidence of metastasis and late-onset relapse cases. Despite several comprehensive genomic studies in medulloblastoma, Group 4 medulloblastomas lack a unifying oncogenic driver and treatment targets. This subgroup is characterized by recurrent genetic alterations in chromatin modifiers, amplification of stemness genes, and enhancer hijacking events. 17% of Group 4 medulloblastoma cases are characterized by enhancer hijacking through tandem duplication of SNCAIP, resulting in high expression of PRDM6, a putative transcriptional repressor and histone methyltransferase. PRDM6 amplified medulloblastoma cases show additional mutations in other chromatin regulators, such as KDM6A, KMT2C and KMT2D, ZMYM3, and high MYCN expression. In this project, we investigate the impact and oncogenic potential of sustained PRDM6 expression in early neural stem cell populations and the developing mouse cerebellum. We drive expression of PRDM6 in human iPSC-derived neuroepithelial stem cells (NESCs) with and without high MYCN expression to study its implications in tumorigenesis. To test for tumor growth in vivo and changes in tumor progression as a function of PRDM6 activity, NESCs are injected into the cerebellum of adult mice. In order to elucidate impact of PRDM6 activity during embryonic cerebellar development, we also introduce PRDM6 expression into mouse embryonic stem cells (ESCs) for analysis via a new, in vivo cerebellar blastocyst complementation model. The latter approach is designed to ablate and repopulate early granule neural precursor cells in the embryonal cerebellum with progenitors derived from injected PRDM6-ESCs and thus to recapitulate pre- and postnatal cerebellar development in vivo. Together, our studies aim to understand the role of PRDM6 during normal cerebellar development and tumorigenesis and advance the understanding of the genetic drivers for Group 4 medulloblastoma.