Microarray comparison of anterior and posterior Drosophila wing imaginal disc cells

Signaling between cells in the Anterior (A) and Posterior (P) compartments directs Drosophila wing disc development and is dependent on expression of the homeodomain transcription factor Engrailed (En) in P cells. Downstream of en, posteriorly expressed Hedgehog (Hh) protein signals across the A/P border to establish a developmental organizer that directs pattern formation and growth throughout the wing primordium. Here we extend investigations of the processes downstream of en by using expression array analysis to compare A and P cells. 102 candidate genes were identified that express differentially in the A and P compartments; four were characterized: Stubble (Sb) expression is restricted to A cells due to repression by en. CG15905, CG16884, and CG10200/hase und igel (hui) are expressed in A cells downstream of Hh signaling; and RNA interference for hui, Stubble, and CG16884 revealed that each is essential to wing development. We carried out a global screen for genes with compartment-specific expression using expression array hybridization to compare transcript levels in A and P wing disc cells. GFP-labeled wing imaginal discs (ptc-Gal4/UAS-GFP and hh-Gal4/UAS-GFP) were micro-dissected under a fluorescence dissecting microscope. RNA isolation, amplification and microarray procedures were previously described (Klebes et al., 2002; Klebes et al., 2005; Klebes and Kornberg, 2008). In brief, hybridization probes were generated by two rounds of T7-catalyzed linear RNA amplification and labeled with Cy3 and Cy5 dyes. Reciprocally labeled probes (‘dye flip’) were hybridized to custom produced glass microarrays (GPL2581) that contained approximately 14,000 100-600 bp exon sequences that were generated by PCR. Signal intensities were collected with a GenePix 4000B Scanner and processed with GenePix software (Molecular Devices) and global median normalized with NOMAD (http://ucsf-nomad.sourceforge.net/).