(A–C) Levels of Ss expression were not significantly different between wild type and klu mutant SsON R7s. A-C are from three representative retinas. ns indicates not significant, p>0.05. Error bars indicate standard deviation (SD). (D–E) Ss levels are not significantly changed in flies with sin, klu null mutants, or flies with increased levels of Klu (eye >klu). We previously showed that changes in Ss levels or activity alter the exclusivity or co-expression of Rhodopsin expression (Thanawala et al., 2013). The main region of the retina is a random mosaic of R7s cells with exclusive expression of Rh3 (SsOFF) or Rh4 (SsON). This exclusivity breaks down in the dorsal third region of the retina where some R7s exclusively express Rh3 (SsOFF), but others co-express Rh4 and Rh3 (SsON). This dorsal third region starts approximately four rows above the dorsal/ventral equator of the retina. Increasing levels of Ss generates retinas with exclusive expression of Rh3 or Rh4 throughout the retina. Decreasing levels of Ss leads to an expansion of the dorsal third region of co-expression. Thus, we used the demarcation of the region of co-expression of Rh4 and Rh3 in SsON R7s as a proxy for Ss levels. (D) Representative image of lab stock Rh3 and Rh4 expression indicating position of the equator (solid green line) and dorsal third region (dashed green line). (E) Quantification of the position of the dorsal third in number of rows above the equator. ns indicates not significant, p>0.05. Error bars indicate standard deviation (SD).