Signal transducer and activator of transcription 5 (STAT5), which is induced by interleukin-7 receptor (IL-7R), and the transcription factors early B cell factor 1 (EBF1), forkhead box protein O1 (FOXO1) and MYB are components of a mutually reinforcing regulatory network that promotes the survival of pro-B cells. This regulatory network programmes the expression of the pro-survival genes B cell lymphoma 2 (BCL2), B cell lymphoma-XL (BCLXL) and myeloid cell leukaemia sequence 1 (MCL1), which are not mutually redundant. The transcription factor MYC-interacting zinc finger protein 1 (MIZ1) stabilizes the network by repressing the suppressor of cytokine signalling 1 (SOCS1) gene, which encodes an inhibitor of Janus kinase (JAK) signalling and STAT5 activation.