RNA-seq of V-SZV derived aNS cells with siRNA mediated depletion of Pbx1, Tcf3 and Tcf4

Developmental transcription factors act in networks, but how these networks achieve cell- and tissue specificity is still poorly understood. Here we explored pre-B cell leukemia homeobox 1 (PBX1) in adult neurogenesis combining genomic, transcriptomic, and proteomic approaches. ChIP-Seq analysis uncovered PBX1 binding to a wide range of different sites. Integration of PBX1 ChIP-seq with ATAC-seq data predicted interaction partners, which were subsequently validated by mass spectrometry. Spatial transcriptomics revealed distinct temporal expression dynamics of Pbx1 and interacting factors. Among these were class I bHLH proteins TCF3, TCF4 and TCF12. RNA-seq upon Pbx1, Tcf3 and Tcf4 knockdown identified proliferation- and differentiation associated genes as shared targets. Neuronal differentiation was reduced upon depletion of either factor, suggesting functional cooperation between PBX1 and TCF3/4. Notably, while physiological PBX1-TCF interactions have not yet been described, chromosomal translocation resulting in genomic TCF3::PBX1 fusion characterizes a subtype of acute lymphoblastic leukemia. Introducing Pbx1 into Nalm6 cells, a pre-B cell line expressing TCF3 but lacking PBX1, upregulated leukemogenic genes including BLK and NOTCH3, arguing that functional PBX1-TCF cooperation likely extends to hematopoietic contexts. Our study hence uncovers a PBX1-TCF module orchestrating the balance between progenitor cell proliferation and differentiation in adult neurogenesis with implications for leukemia etiology.