GEOapplication/xmlftp://ftp.ncbi.nlm.nih.gov/geo/series/GSE343nnn/GSE343852/primaryOK200TranscriptomicsMus musculus Genome binding/occupancy profiling by high throughput sequencingExpression profiling by high throughput sequencinghttps://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE343852GEOGSEfalseEzh2-Y641F mutations are distinct from EZH2 overexpression and impact germinal center B cells in a timing-dependent mannerGerminal center (GC) B cell-derived Non-Hodgkin Lymphomas (NHL) frequently exhibit gain-of-function alterations in the H3K27 methyltransferase EZH2, including a heterozygous, somatic hotspot mutation at position Y646 (Y641 in mice) or overexpression of wild-type protein (EZH2OE). To determine whether Ezh2Y646 mutations and EZH2OE are functionally equivalent or distinct gain-of-function events in GC B cells, we directly compared EZH2Y641F/+ and EZH2OE using conditional mouse models that activate these events either throughout the B lineage or specifically within GC B cells. Across transplant and non-transplant settings, we found that EZH2OE yields surprisingly weak phenotypes, while EZH2Y641F/+ causes strong but timing-dependent effects in GC cells. We observed that GC-specific EZH2Y641F/+ causes GC expansion and promotes lymphoma phenotypes, whereas early B lineage activation reduced GC fitness. Furthermore, transcriptional analysis and H3K27me3 profiling revealed that EZH2OE and EZH2Y641F/+ are non-equivalent molecular events. EZH2OE minimally impacted gene expression and H3K27me3 profiles compared to controls, while EZH2Y641F/+ caused widespread differential gene expression and broad redistribution of H3K27me3. The extent and localization of the redistribution depend on when the mutation is activated in the B lineage, potentially explaining why early vs. GC-restricted EZH2Y641F produce disparate GC phenotypes. Ultimately, we determined that EZH2Y641F/+ and EZH2OE are functionally distinct events, with only GC-restricted EZH2Y641F/+ contributing to GC B cell transformation phenotypes. Our evidence supports the conclusion that EZH2Y641F/+ is a neomorph of EZH2WT rather than a pure gain-of-function event and reveals the context-dependent nature of its role in B-NHL.2026/09/10GSE343852GSM10043094GSM10043095GSM10043096GSM10043097GSM10043090GSM10043091GSM10043092GSM10043093GSM9963661GSM9963660GSM10043087GSM9963663GSM9963662GSM10043088GSM9963665GSM10043089GSM9963664GSM9963667GSM9963666GSM9963669GSM9963668GSM10043083GSM10043084GSM10043085GSM10043086GSM10043080GSM10043081GSM10043082GSM9963650GSM9963652GSM10043076GSM10043110GSM9963651GSM10043077GSM10043078GSM9963654GSM10043111GSM9963653GSM10043079GSM9963656GSM9963655GSM9963658GSM9963657GSM9963659GSM10043102GSM9963681GSM9963680GSM10043103GSM10043104GSM9963683GSM9963682GSM10043105GSM9963641GSM9963640GSM9963643GSM10043100GSM9963642GSM10043101GSM9963645GSM9963644GSM9963647GSM9963646GSM10043106GSM9963649GSM10043107GSM9963648GSM10043108GSM10043109GSM9963670GSM9963672GSM9963671GSM10043098GSM9963674GSM9963673GSM10043099GSM9963676GSM9963675GSM9963678GSM9963677GSM9963636GSM9963679GSM9963638GSM9963637GSM996363934290343852Mus musculus