Homeotic control in Drosophila; the scabrous gene is an in vivo target of Ultrabithorax proteins.

The regulatory functions of transcription factors encoded by the Ultrabithorax (Ubx) gene initiate genetic programmes essential for segmental identity and morphogenesis in Drosophila. Based on the formation of DNA-protein adducts in intact nuclei and immunoselection procedure, we cloned genomic targets for Ubx proteins. One clone was studied in detail. It encompasses parts of the last intron and exon of the scabrous (sca) gene, which encodes a secreted protein involved in cellular communication during neurogenesis. Five motifs, presenting the ATTA core, which is shared by most homeodomain binding sites, were found in the nucleotide sequence of this clone. We detail here the dynamic pattern of sca transcript accumulation during embryogenesis and show that mutation of Ubx results in the ectopic transcription of sca in the first abdominal segment. We propose that a direct interaction of Ubx with cis-acting elements in sca negatively regulates the gene. Transcript localization in several combinations of deficiencies in the Bithorax complex (BX-C) indicates that sca is downregulated by abdominal A (abdA) and Abdominal B (AbdB), and suggests that it is a common target of the three genes of BX-C.