Ezh2 Delays Activation of Differentiation Genes During Normal Cerebellar Granule Neuron Development and in Medulloblastoma

Reviewer #1 (Public review):

In this manuscript, Purzner and colleagues examine the role of Ezh2 in cerebellar development and tumorigenesis using animal models of SHH medulloblastoma (MB). While Ezh2 plays a relatively minor role in granule neuron development and SHH MB, the authors demonstrate that Ezh2 inhibition, when combined with enforced cell cycle exit, promotes MB cell differentiation and potentially reduces malignancy. Overall, this study is solid and provides valuable insights into Ezh2 regulation in cerebellar development and SHH-MB tumorigenesis.

Strengths:

The authors investigate the role of Ezh2 in granule neuronal differentiation during cerebellar development and medulloblastoma (MB) progression, integrating multi-omics for a comprehensive epigenetic analysis. The use of Ezh2 conditional knockout (cKO) mice and combination therapy with Ezh2 and CDK4/6 inhibitors shows a promising strategy to induce terminal differentiation in MB cells, with potential therapeutic implications. Additionally, analysis of human SHH-MB samples reveals that higher EZH2 expression correlates with worse survival, indicating the clinical relevance.

Weaknesses:

The study does not fully explore compensatory mechanisms of PRC2 given that the phenotype of Ezh2 conditional knockout (cKO) in GNP development and MB tumor formation is relatively mild.

Reviewer #2 (Public review):

Summary:

This study used an unbiased approach to evaluate epigenetic dynamics during the differentiation of granule neuron precursors, the cell of origin for Shh-MB. These profiling findings led to the focus on H3K27me3 dynamics, which correlate with the remodeling of epigenetic landscape associated with neuronal differentiation gene activation.

Strengths:

Depletion of EZH2, an enzymatic subunit of PRC2, resulted in premature neuronal differentiation in the developing cerebellum.

Weaknesses:

Little information is shown about the specific genetic programs disrupted by EZH2 depletion. This is a crucial weakness as existing PRC2 inhibitors do not effectively cross the blood-brain barrier. Further studies are necessary to identify downstream targets of PRC2 that could be targeted to induce neuronal differentiation in MB cells.