Fig. 3. otk is not required for R-cell differentiation and cell fate determination. Third-instar eye-imaginal discs were stained with anti-Prospero (A,B) or anti-Boss antibody (C,D). In wild type, each ommatidium contains only a single R7 (R7 nucleus indicated by arrow in A) and a single R8 cell (cell apical surface indicated by arrow in C). In an otk³ mosaic eye-imaginal disc, only one R7 (B) and one R8 (D) were present in each ommatidium. Tangential sections of wild-type (E) and otk³ adult mosaic eyes (F) did not reveal any defect in either the number or the organization of R cells within each ommatidium. The arrow in F indicates a wild-type ommatidium surrounded by dense pigment granules. The arrowhead in F indicates an otk³ mutant ommatidium that can be recognized by the absence of pigment granules. Scale bar: 10 µm.