RAG1 and lymphoma: MCL-1 is critical for the survival of rapidly proliferating hematopoietic progenitors36 and non-transformed pro-B/pre-B cells,12 the cells thought to be the origin of Eμ-Myc lymphoma.37, 38 Therefore, we examined the role of MCL-1 in pre-B/B cell lymphoma development in Eμ-Myc transgenic mice by incorporating CD19-Cre or Rag1-Cre alleles to impose Mcl-1 gene deletion exclusively in the B-lymphoid compartment.