Effect of heterozygous alleles on transgene expression.

(A) Third instar eye imaginal disc expressing UAS-GFP.nls under ey-Gal4. Mean GFP fluorescence intensity was used as a proxy for assessing variation in ey-Gal4 activity. GFP fluorescence was quantified in the posterior region of eye discs (white box) using the Photoshop Measurement feature. The following genotypes were analyzed: (B) ey-Gal4/+; UAS-GFP.nls/suppressor alleles and (C) ey-Gal4/+; UAS-GFP.nls/enhancer alleles as indicated on the panels. Fluorescence intensities are normalized to CTL (ey-Gal4/+; UAS-GFP.nls/+). Error bars represent standard deviations (SD) from at least three independent experiments. The green and red stars highlight a statistically significant (p≤0.05, Student’s t-test) increase or decrease in GFP fluorescence, respectively. (D) Amino acid sequence alignment of PBX-interacting regions from Drosophila HTH and human MEIS-related homeobox proteins. Identical amino acids are shown in red, whereas similar amino acids are shown in blue. The position of the amino acid change (K180N) found in the hthS-195 allele is shown on top of the HTH sequence. (TIF)