Open Collections

Abstract

Medulloblastoma (MB) is the most common malignant pediatric brain tumor and comprises four major molecular subgroups: WNT, SHH, Group 3 (MBG3), and Group 4 (MBG4). Among these, MBG3 is the most aggressive, yet its developmental origin remains poorly defined. While WNT, SHH, and MBG4 tumors have been linked to distinct cerebellar progenitor lineages, the cell type giving rise to MBG3 remains uncertain. Recent single-cell transcriptomic studies suggest that MBG3 tumors arise from early rhombic lip–derived progenitors, but the specific lineage within this compartment has not been resolved. This thesis tests the hypothesis that MBG3 originates from cerebellar nuclear (CN) neurons, early-born excitatory projection neurons that share molecular features and developmental timing with MBG3 progenitor-like cells. To address this, I integrated multiple large-scale single-cell RNA sequencing (scRNA-seq) datasets from embryonic mouse cerebellum (E10.5–E18.5) to define CN-specific transcriptional programs and distinguish them from those of unipolar brush cells (UBCs), a closely related lineage and the proposed origin of MBG4. Using differential expression, lineage-specific marker analysis, and cross-dataset integration (SCTransform + Harmony), I identified a compact CN-specific marker panel (Lhx2, Lhx9, Evx1, Sst, Th) that reliably separates CN from UBC populations. These CN-specific signatures were then mapped to human MBG3 and MBG4 tumors using integrated scRNA-seq and pseudobulk DESeq2 analyses across multiple patient cohorts. CN-associated genes were significantly enriched among MBG3-upregulated transcripts, whereas UBC-like programs predominated in MBG4. The neuropeptide SST and transcription factor LMO1 emerged as the most strongly CN-aligned markers within MBG3, suggesting that subsets of CN developmental programs are selectively re-activated in this subgroup. Together, these results support a developmental continuum model in which MBG3 and MBG4 arise from related rhombic-lip lineages, with MBG3 reflecting CN-like progenitor states and MBG4 reflecting UBC-like differentiation trajectories. This work clarifies the developmental alignment of MB subgroups, refines CN-specific molecular definitions, and provides lineage-anchored biomarkers that may improve tumor classification and provides a framework that could inform future experimental work aimed at therapeutic targeting of Group 3 medulloblastoma.