RAG1 and acute lymphoblastic leukemia: Interestingly, although RAG1 is expressed by mammalian B-lymphoblasts and T-lymphoblasts, we find that only D. rerio T-lymphoblasts express rag1 highly, with levels >70- and >155-fold greater in normal T or T-ALL cells than in B or pre-B ALL cells, respectively (Fig. 3A(e), S2A(e), 5, 6C,E).