Loss of MYB expression results in worse outcome in ALL. A Map of common insertion sites in the Myb gene; numbers refer to number of insertions at a specific site. B qRT-PCR for Myb normalized to Actin in progenitor B cells isolated from the bone marrow of C57Bl/6 (black, n=4) mice, and leukemic cells isolated from the lymph nodes of Pax5+/−xEbf1+/− (purple, n=6) and SB Pax5+/−xEbf1+/− mice. The samples from the SB Pax5+/−xEbf1+/− mice were split between those without (red, n=17) or with (blue, n=8) an insertion in the Myb locus. Significance was tested using an ordinary one-way ANOVA with Holm-Sidak’s multiple comparison test and the lines represent median. C Log2 transformed fragments per kilobase of exon model per million reads mapped (FPKM) values from C57Bl/6 (black filled, n=3), Ebf1+/−(green open, n=4), Pax5+/−(green filled, n=4), Pax5+/−xEbf1+/− pre-leukemic (purple open, n=4), Pax5+/−x Ebf1+/− leukemic (purple filled, n=7), and SB Pax5+/−xEbf1+/− leukemic samples without (red filled, n=21) or with (blue filled, n=10) a transposon insertion. Significance was tested using a Kruskal-Wallis test with Dunn’s multiple comparison test and the line represents median. D Western blot analysis showing decreased expression of MYB in SB leukemia samples harboring a transposon insertion. The + or − indicates the presence or absence of a SB transposon insertion in each representative sample. E Plotted ratio of MYB to actin from the western blot in panel d. Samples without a transposon insert are red (n=4) and those with a transposon insert are blue (n=8). Significance was determined using an unpaired student t-test and the line represents the median. F Linear regression analysis comparing date of death versus FPKM value for leukemic samples harboring a transposon insertion. The dashed lines represent 95% confidence bands.