Fig. 2. Bar expression in the basal undifferentiated cells depends on a posterior secreted signal. (A-C) Morphogenetic furrow can be formed and progresses in ato¹ mutant eye disc. The furrow is shown by apical membrane constriction intensely stained by Dlg membrane marker (B, arrow) and by Ato expression (C, arrow) in the middle of ato¹ mutant eye disc. (D-F) A graded Bar expression in ato¹ mutant eye disc. Bar is expressed posterior to the furrow in ato¹ mutant eye disc. Bar expression level is high near the posterior margin but decreases significantly near the furrow, suggesting that Bar expression may depend on a secreted factor(s) from the posterior margin (F). An area marked with a rectangle in E is magnified in F. MF, morphogenetic furrow.