Fig. 4. Delayed FC differentiation and ectopic polar cells occur in slmb somatic clones. (A) In wild-type ovarioles, Fas3 expression (red) refines as oogenesis progresses and from stage 4 onwards becomes restricted to polar cells (arrows). (B) In slmb FC clones, Fas3 remains widespread (egg chambers are outlined). (C) In egg chambers bearing slmb FC clones, large patches of cells expressing Fas3 are still detected at stage 9 (arrow). Mutant clones from the egg chamber shown in C were positively marked with GFP (D, arrow) and the merged confocal image shows that ectopic Fas3 correlates with the position of the clones (E, arrow). Arrowheads in C-E mark a pair of cells that are probably ectopic polar cells. (F-H,J) The PZ80 enhancer trap is specifically expressed in polar cells. In wild-type ovaries at stage 8, the two pairs of polar cells are localized at the anterior and posterior termini of the follicle (F, arrows) at stage 8; at stage 9, anterior polar cells migrate posteriorly between nurse cells (G, arrow); and at stage 10, they have reached the anterior border of the oocyte (H, arrow). (I,K) The slbo-LacZ element is expressed in border cells. In stage 10 wild-type follicles, border cells can be seen at the anterior end of the oocyte (I, arrow). Egg chambers bearing slmb FC clones often exhibit extra polar cells (J, arrowhead) and differentiate ectopic clusters of border cells (K, arrowhead). In these follicles, border cell migration is often delayed and by stage 10, they are located between nurse cells (J,K, arrows).