Fig. 6. Unpaired signaling from polar cells is limited in range. (A-B) Anti-GFP staining (green), monitoring JAK/STAT activation using the 2XSTAT92E-GFP reporter. Anti-ß-gal staining (A', red) of the Notch reporter m7-lacZ. During early stages of oogenesis, Upd signaling from the polar cells is capable of inducing strong STAT activation in stalk cells (arrows in A,A'), but fails to elicit activation in either the polar cells themselves, or in the neighboring main-body follicle cells. At later stages, follicle cell populations, including main-body and border cells, exhibit concomitant Notch and STAT activation (arrowheads in A,A',B). (C,C') Localization of STAT in early follicle cells. Ovarioles in which polar cells were visualized by A101-GAL4/UAS-GFP (green), were stained for STAT (red) and the nuclear marker DAPI (blue). Nuclear localization of STAT staining (boxes) shows the limited range of JAK/STAT activation by Upd emanating from polar cells. STAT staining alone (C) demonstrates the non-responsiveness of the polar cells to the Upd signal they produce, as STAT does not localize to polar cell nuclei (arrowhead in C, enlarged view). (D,D') Overexpression of Upd using the A101-GAL4 polar cell-specific driver. The range of JAK/STAT activation (monitored by nuclear localization of STAT, red) broadens exclusively towards the anterior. Polar cells remain refractory to the signal (arrowhead). (E) DAPI staining of egg chambers overexpressing Upd in polar cells reveals an abnormally long stalk (arrow). (F,F') Main-body follicle cell clones homozygous for N^55e11 (marked by loss of GFP), display nuclear localization of STAT (arrow), demonstrating that Notch activation in these cells antagonizes the JAK/STAT pathway. Clones that were further than four cell-diameters from the polar cells did not display nuclear STAT, owing to the restricted diffusion of Upd (not shown).