Fig. 4.

Activation of DRA rhodopsin expression by Hth/Exd requires Orthodenticle. (A) From top to bottom: expression of rh1-, rh3- and rh6-lacZ (X-Gal reaction on adult eye sections), followed by a summary of the retinal mosaics. (B) rh3-lacZ expression was lost in otd^UVI mutants and rh6-lacZ expanded into R1-6, labeling axon projections to the lamina (arrow). (C) Summary of hth gain of function: rh3-lacZ was expanded into all inner photoreceptors (projections to the medulla), rh1-lacZ was normal, and rh6-lacZ lost. (D) Overexpression of Hth in otd^UVI mutants led to loss of both rh3- and rh6-lacZ, whereas only rh1-lacZ expression remained. (E) Expression of Hth (green) was normal in homozygous pupal clones of otd² (dashed line), marked by absence of Armadillo-lacZ (E′). (F) DRA specification, marked by Exd (red) in R7 and R8, appeared normal in otd^UVI mutants. (G) Hth remained expressed specifically in the DRA (green) of adult otd^UVI mutants. L, lamina; M, medulla.