Summary Ependymoma is a heterogeneous entity of central nervous system tumors with well-established molecular groups. Here, we apply single-cell RNA sequencing to analyze ependymomas across molecular groups and anatomic locations to investigate their intratumoral heterogeneity and developmental origins. Ependymomas are composed of a cellular hierarchy initiating from undifferentiated populations, which undergo impaired differentiation toward three lineages of neuronal-glial fate specification. While prognostically favorable groups of ependymoma predominantly harbor differentiated cells, aggressive groups are enriched for undifferentiated cell populations. The delineated transcriptomic signatures correlate with patient survival and define molecular dependencies for targeted treatment approaches. Taken together, our analyses reveal a developmental hierarchy underlying ependymomas relevant to biological and clinical behavior.

ETMRs are aggressive pediatric embryonal brain tumors with universally dismal outcome1. We collected 193 primary ETMRs and 23 matched relapses to investigate the genomic landscape of this distinct entity. We found that patients having tumors without C19MC amplification, the proposed driver [3][4][5] , frequently harbor DICER1 germline mutations or other miRNA-related aberrations including somatic miR-17-92 amplifications. Whole-genome sequencing revealed an overall low recurrence of SNVs, but prevalent R-loop-associated chromosomal instability, of which we show that this can be induced by loss of DICER1 function. Comparing primary tumors and matched relapses revealed a strong conservation of SVs but low conservation of SNVs. Moreover, many newly acquired SNVs are associated to a new cisplatin treatment related mutational signature. Finally, we show that targeting R-loops with topoisomerase and PARP inhibitors might be an effective treatment strategy for this deadly disease.Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use: