(a) Optical cross-section of a WT stage 7 follicle stained with FasIII (polar cell marker, white) and F-actin (red). (b) Expression of the 10xStatGFP reporter showing the progressive formation of a STAT gradient at each pole. Early elongation is affected by (c) knocking down upd in polar cells or (d) the expression of Stat92E in the anterior and posterior follicular cells. Early elongation is also affected by (e) clonal ectopic expression of upd (GFP-positive cells) and by (f) expression of a Hop gain of function mutant in all follicular cells. (g) Quantification of the elongation coefficient in WT and the different JAK-STAT loss- and gain-of-function genotypes — corresponding to Upd:GAL4 and Upd-RNAi, Fru:GAL4 and STAT92E-RNAi, and Tj:GAL4 and UAS:Hoptum — during early and intermediate stages of elongation (D, Driver; U, UAS line). (For each point n > 30; p *<0.05, **<0.01, ***<0.001.) (h) Quantification of the Stat activity gradient at stages 3, 5 and 7 using the 10XSTATGFP reporter. A gradient is already visible at stage 3 and becomes more visible until stage 7. Scale bars are 10 μm throughout. Relative intensity = intensity at a given position/mean intensity of measured signal. Full details of the genotypes and sample sizes are given in the supplementary files.