Function of the spalt/spalt-related gene complex in positioning the veins in the Drosophila wing

Spalt and Spalt-related encode conserved Zn-finger proteins that mediate th e function of the TGF-beta molecule Decapentaplegic during the positioning of veins in the Drosophila wing. Here we show that Spalt and Spalt-related regulate the vein-specific expression of the transcription factors of the k nirps and iroquois gene complexes, delimiting their domains of expression i n the wing pouch. The effects of spalt/spalt-related mutations on knirps an d iroquois expression are cell-autonomous, suggesting that they could be di rect. The regulation of iroquois involves transcriptional repression by Spa lt and Spalt-related, whereas the regulation of knirps involves a combinati on of transcriptional activation and repression mediated by the same genes. We suggest that the regulation of the iroquois and knirps gene complexes b y Spalt and Spalt-related translates the Decapentaplegic morphogenetic grad ient into precisely spaced pattern elements. (C) 2000 Elsevier Science Irel and Ltd. All rights reserved.