Depletion of H1 enhances hematopoietic tumor formation caused by hyperactive JAK but does not affect JAK/STAT transcriptional activity. (A) L3 larvae with a hopTum-l mutation (left) exhibit hematopoietic tumors (white arrows) when reared at 29°C. When H1 is simultaneously depleted in hopTum-l larvae, both the size and the number of tumors are significantly increased throughout the larval body (the three panels on the right demonstrate a spectrum of observed phenotypes). For quantitation, see Table 1. Scale bar represents 1 mm. (B) Homozygous flies that carry an eGFP transgene under control of a promoter with 10 upstream STAT92E binding sites (10xSTAT92E-GFP) were mated with appropriate counterparts, wild type; hopTum-l allele; H1 knockdown (KD) pINT1-H14M, Actin-GAL4 allele; or a combined H1 knockdown, hopTum-l allele, at 29°C, and eGFP expression was examined in the progeny by GFP autofluorescence. hopTum-l mutation but not H1 depletion strongly enhances the expression of eGFP. Scale bar represents 1 mm. (C) Semi-quantitative western analyses of eGFP reporter expression in whole larvae. Wild type; hopTum-l; pINT1-H14M, Actin-GAL4; and hopTum-l, pINT1-H14M, Actin-GAL4 flies were crossed with 10xSTAT92E92E-GFP reporter flies, and proteins in lysates of whole L3 larvae in the F1 progeny were analyzed by western blot. Anti-tubulin western was used as a loading control. H1 KD H1 knockdown. (D) For eGFP quantitation, the GFP staining intensity in western blots (C) was normalized to that of tubulin and plotted. In the hopTum-l background, the expression of eGFP reporter is approximately four times higher than that in the wild type background and is further stimulated (approximately 1.5-fold) by H1 knockdown, whereas H1 depletion alone does not appreciably affect eGFP expression. The quantitation is based on three independent experiments. Error bars represent standard deviation.