Fig. 4. Non-overlapping UVRh, BRh1 and BRh2 expression in R1 and R2 photoreceptor cells. (A-C) Ventral views. (A) Tangential section showing UVRh expression in R1 and R2 photoreceptor cells in the ventral retina. (B) Section adjacent to A showing BRh1 mRNA expression in R1 and R2 cells in the ventral retina that was non-overlapping with UVRh expression. Broken circles in each panel indicate identical ommatidia in adjacent sections. (C) Section adjacent to B showing BRh2 expression in R1 and R2 cells in the ventral retina that was non-overlapping with UVRh and BRh1 mRNA expression. Five different types of ommatidia are depicted in each panel: UVRh-UVRh (one arrowhead), UVRh-BRh1 (short arrow); UVRh-BRh2 (double short arrows); BRh1-BRh1 (long arrow); BRh1-BRh2 (double arrowheads). A sixth combination BRh2-BRh2 was also observed (data not shown). (D-F) Dorsal views. (D) Tangential section showing UVRh expression in nearly all R1 and R2 cells in the dorsal retina. (E) Tangential section showing BRh1 expression in a small number of R1 and R2 (and all R3-R8) cells in the dorsal retina. Inset (big square) shows BRh1 expressed in R1, as well as R3-8 cells; small square shows BRh1 expressed in R1-R8 cells. (F) Section adjacent to D showing no BRh2 mRNA expression in dorsal retina. Broken circles indicate identical ommatidia in adjacent sections. Three different types of ommatidia were found: UVRh-UVRh (arrowhead), UVRh-BRh1 (short arrow), BRh1-BRh1 (long arrow).