Isolation of ktub mutants by P-element excision. Schematic drawing indicates the gene structure of Drosophila king tubby (ktub) gene (A). The P-element (GSV6)17325 is inserted in the first exon of ktub gene. Fly genomic annotation indicates that ktub gene has two transcripts and two polypeptides; the long form (L) and short form (S), which are activated by distinct promoters. Arrows indicate two PCR primers, which were used to screen for the imprecise excision of ktub mutants (B). ktub115-4 and ktub35-3 mutants deleted 1.6 kb and 1.3 kb, including the translation start site of the long form transcript, respectively (B). Western blotting indicates the reduced of Ktub expression in mutant flies (C, arrowhead). Confocal images reveal that the expression of Ktub decreases significantly in mutant photoreceptor cells (D). Green indicates anti-Ktub antibody, and red is rhodamine-phalloidin. The scale bar is 10 μm.