Fig. 4. Posterior margin smo mutant clones block Eya expression and photoreceptor differentiation. (A-G) The same eye disc stained with anti-ß-galactosidase (red in A,D,E,G), anti-Eya (cyan in B,D), anti-Elav (green in F,G) and anti-Senseless, an R8 photoreceptor-specific marker (green in C,D). The clone boundaries are marked with broken white lines (A,D,E,G). (C,D,F,G) smo clones are negatively marked by the absence of ß-galactosidase and lack expression Senseless (C,D) or the pan-neuronal marker Elav (F,G). (B,D) Loss of Eya expression in posterior margin clones (B; yellow arrow in D) and a reduction of Eya expression internally in large smo clones (white arrow in D). (D,G) Furrow progression is delayed in internal smo clones, but up to two rows of photoreceptor clusters differentiate in mutant tissue (yellow arrowheads in D,G).