a-b, BCL6 mRNA (a) and protein (b) in heat-shocked human adult fibroblasts, murine BCL1 B-cells, dog Cf2Th thymocytes, iguana IgH-2 epithelial cells, chicken DT40 B-cells, zebrafish embryos and sea lamprey typhlosole tissue (n=3 biological replicates). c-d, Serial stress assays where cells were heat shocked once (tan) or serially heat shocked (red). Fold change of cell death in murine B220+ splenocytes from Bcl6+/+ and Bcl6−/− (n=3–5 mice per group) (c) or zebrafish embryos injected with control or bcl6 morpholino (mo) (n=3 biological replicates, 75–100 embryos per experiment) (d). See Supplementary Fig. 4d for immunoblots and QPCR of BCL6 knockdown. P values were calculated by two-sided T-test. Data presented as mean ± s.e.m.