Characterization of ID3 loss in BL. (A) The mutational landscape of ID3 mutations found in BL with all 3 subtypes manifesting similar mutational patterns. (B) Proteomics analysis of proteins bound to WT ID3 in BL cell lines. (C) Quantitative PCR (qPCR) data showing diminished ID3 expression in CRISPR knockout (KO) cell lines. (D) RNA-seq data revealing differentially expressed genes between WT and ID3 CRISPR-engineered cell lines. (E) GSEA-identified cell cycle genes as being upregulated in ID3 CRISPR-engineered cells lines. (F) ID3 silencing is associated with increased incorporation of BrdU, indicating increased proliferation. (G) qPCR data showing diminished TCF4 expression in CRISPR- engineered cell lines. (H) TCF4 silencing is associated with decreased incorporation of BrdU, indicating decreased proliferation. (I) Tumor development and overall survival in Eµ-Myc⁺; Id3^+/− (n = 10) mice compared with Eµ-Myc⁺; Id3^+/+ (n = 8) mice. (J) Flow cytometry analysis of B220/TCR and IgD/IgM of Id3^fl/+; AID-Cre⁺; Eµ-Myc^Tg/0 tumors. (K) Tumors from Id3^fl/+; AID-Cre^Tg/0; Eµ-Myc^Tg/0 conditional knockout crosses show a starry sky pattern. (L) Tumors from Id3^fl/+; AID-Cre^Tg/0; Eµ-Myc^Tg/0 conditional knockout crosses have high Ki-67 expression. H&E, hematoxylin and eosin. Error bars represent standard error of the mean. Microscopy images are at ×10 magnification.