Fig. 5. Upd misexpression stimulates stalk cell production. In wild-type ovaries (A) enhancer trap A101 marks polar follicle cells in the vitellarium. When upd is misexpressed (B-F), polar and stalk cells are mis-specified. Chronic expression of hs-upd results from shifting adults to 30°C (B-F). (B) This treatment causes the frequent loss of polar cell clusters (arrowheads) and development of expanded and morphologically abnormal stalks (arrow). (C-F) The abnormal stalks are not monolayer and often traverse the outside of the chambers to form a continuous ‘rope’. (D, D') The cells in these ropes strongly express Fas III (green) which does not mark normal stalks. However, markers for mature stalk cells, 93F (blue stain in C) and -spectrin (yellow, E, E'), are also abundant in ropes. (F, F') Fusions of egg chambers and mislocalization of the oocyte (asterisk), similar to loss-of-function phenotypes, can occur in chronic upd misexpression, as revealed by Orb accumulation (red).