TBIO-09. IN SILICO ANALYSIS IDENTIFIES A PUTATIVE CELL-OF-ORIGIN FOR BRAF FUSION-POSITIVE CEREBELLAR PILOCYTIC ASTROCYTOMA

Childhood cancers are increasingly recognized as disorders of cellular development. This study sought to identify the cellular and developmental origins of cerebellar pilocytic astrocytoma, the most common brain tumor of childhood. By leveraging publicly available gene expression data from such tumors and controlling for driver mutations, a set of eight known neuro-developmental genes were identified as being upregulated in cerebellar pilocytic astrocytoma. Mapping those genes onto mouse neuro-developmental atlases identified significant overlap in their expression within the ventricular zone of the cerebellar anlage. Further analysis with a single cell RNA-sequencing atlas of the developing mouse cerebellum defined this overlap as occurring in ventricular zone progenitor cells at the division point between GABA-ergic neuronal and glial lineages, a developmental trajectory which closely mirrors that previously described to occur within pilocytic astrocytoma cells. Furthermore, ventricular zone progenitor cells and their progeny exhibited evidence of MAPK pathway activation, the paradigmatic oncogenic cascade known to be active in cerebellar pilocytic astrocytoma. Gene expression from developing human brain atlases recapitulated the same anatomic localizations and developmental trajectories as those found in mice. Taken together, these data suggest this population of ventricular zone progenitor cells as the cell-of-origin for BRAF fusion-positive cerebellar pilocytic astrocytoma.