Figure 4. Rap1 is required for proper ommatidial cell development.

Wildtype (A,C,E,G) or Rap1 mutant (B,D,F,H–J) clones of cells (GFP negative) were generated using the Flp/FRT system. An ey-flp transgene was used to generate clones from the earliest stages of eye development. Larval eye imaginal discs were stained for E-cadherin (E-cad) (A,B), dpERK (C,D), Sens (E,F), Elav (G,H), Ro/Elav (I). 40-hour APF pupal disc was stained for Cut/Elav (J). An arrowhead marks the position of the morphogenetic furrow (A’–F’). (A) E-cadherin is expressed at high levels in the furrow. Cells in the furrow form rosettes (left arrow), which reorganize into arcs (middle arrow); the arcs close to form clusters, each of which is the precursor of an ommatidium. E-cadherin is maintained at high levels in arcs and clusters, but not in intervening cells. (B) E-cadherin staining reveals that cells in Rap1- tissue form morphologically abnormal arcs and clusters (arrows). (C) In wild-type eye discs, high levels of di-phosphorylated MAPK (dpERK) are present in intermediate groups, with lower levels behind the furrow. (D) dpERK levels and spacing intermediate groups is not affected by Rap1- clones. (E) Senseless is expressed in R8 equivalence groups (left arrow) and at high levels in R8 (an Egfr-independent cell type). (F) Senseless expression in R8 equivalence groups is normal, and Senseless-expressing R8 cells are present in Rap1 mutant clones, although their spacing is altered. (G) Elav marks post-mitotic neurons, normally found in clusters posterior to the morphogenetic furrow. (H) In Rap1 mutant clones, Elav clusters are often irregularly shaped (arrows), suggesting a loss of photoreceptor precursors. Rough most strongly labels R2 and R5, and ommatidia containing a single Rough positive cell are frequently found in and around Rap1 mutant tissue (I, arrows). Cut localizes to cone cells, which are frequently lost from Rap1 clones (J), including from ommatidia containing a full complement of photoreceptors (arrows).