Spalt-mediated dve repression is a critical regulatory motif and coordinates with Iroquois complex in Drosophila vein formation

Veins are longitudinal cuticular structures that maintain shape of the wing. Drosophila melanogaster has six longitudinal veins (L1–L6) and two cross veins. The Zn-finger transcription factors of Spalt-complex (Sal) are required for positioning of the L2 and L5, and the homeodomain transcription factors of Iroquois complex (Iro-C) are required for formation of the L3 and L5 veins. The homeodomain transcriptional repressor Defective proventriculus (Dve) is uniformly expressed in the wing pouch of the larval imaginal disc. However, dve mutant wings showed loss of the L2 and L5, but not of the L3 and L4 veins. Temporal dve knockdown experiments indicate that the Dve activity is required for vein formation from late third larval instar to the prepupal stage. In the prepupal wing, Dve expression becomes nearly complementary to that of Sal through the Sal-mediated dve repression. Furthermore, coexpression of Dve and Iro-C relieved of Sal-mediated repression is required for the L5 formation in a dose-dependent manner. The relationship between Sal, Dve, and Iro-C in wing vein specification is quite similar to that in ommatidial cell-type specification. Our results provide information about the conserved function of dve regulatory motifs in cell differentiation.