Figure 4. EB-derived upd2 is essential for tumour growth and ISC maintenance.

(a) AMG of 10-day-old Sox21a flies stained for 10xSTAT-GFP^D(green) shows increased JAK/STAT activity in the tumour (indicated by a star). (b) AMG containing GFP-labelled Sox21a mutant clone stained for dpERK (red) at 16 days ACI. dpERK staining is observed around the Sox21a clone. (c) Tumour burden of flies with the indicated genotypes kept at 25 °C (mutant analysis) or 29 °C (overexpression analysis) for 21 days. Enh::Sox21a is a rescue construct with Sox21a under the control of its own enhancer sequence. ‘EB>' refers to the EB driver GBE^TS, and ‘EC>' refers to the enterocyte driver Myo1A^TS. Numbers of flies scored for each genotype are indicated. (d,e) Expressing GFP (d, control) or upd2-RNAi (e) in EBs of Sox21a flies placed for 21 days at 29 °C. Gut was stained with Armadillo (Arm; red, plasma membrane for progenitors) and Prospero (Pros, red, nuclear, for enteroendocrine cells). EBs are marked by GBE>GFP (green). (f-g) AMG of flies depleted for Notch (N) alone (f) or in combination with upd2 (g) for 4 days at 29 °C. The expression of upd2-IR in progenitors reduced tumour formation. (h,i) AMG of flies expressing GFP (control, h) or upd2-RNAi (i) in the progenitor cells using the esg^TS driver for 14 days at 29 °C shows that upd2 is required for basal stem cell maintenance. Progenitors are shown by esg>GFP in green (f–i) and by Arm immunostaining (h,i). P values in c (repeated three times) from χ²-test (*P<0.05; **P<0.01; ***P<0.001). Each other individual image shown in a,b and (d–i) represents 20 flies tested in one experiment repeated three times.