Fig. 2. Mutations in echinoid lead to formation of multiple R8 cells per ommatidium. (A) Atonal expression (green) narrows to a single cell posterior to the morphogenetic furrow in wild-type discs. (B) In homozygous ed^l(2)k01102 eye discs, multiple cells often retain Atonal expression (arrows). (C,D) Similarly, when ed^l(2)k01102 patches of tissue are created using the FLPFRT technique (loss of green GFP marker), Atonal expression (red) within the patch fails to narrow to a single cell. (E) In wild-type tissue, one mature R8 photoreceptor is present in each ommatidium, as visualized with an antibody against Boss (red). (F) Multiple Boss-expressing cells are present in many ommatidia of ed^l(2)k01102discs. (G,H) Using the FLP-FRT technique to create homozygous ed^l(2)k01102 patches of tissue (loss of green) shows a similar multiple R8-phenotype by Boss staining (red). (I,J) In wild-type tissue (I), an antibody against Senseless detects one R8 photoreceptor per ommatidium, but in ed^l(2)k01102/ed^slA12 discs (J) many ommatidia contain multiple R8 cells (arrow). (K,L) In adult eyes, both R7 and R8 cells are distinguished by a small inner rhabdomere; the rhabdomere of the R7 cell is present in the apical portion of the eye, while the R8 rhabdomere is visible in more basal sections. Sections of adult eyes containing FLP-FRT-mediated clones of echinoid tissue show multiple inner rhabdomeres present in basal sections (arrow, K), but not necessarily in apical sections of the same ommatidia (arrow, L). Because the mutation used for these experiments is marked with the white gene, clonal boundaries cannot be discerned in these sections.

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