The UBX-regulated network in the haltere imaginal disc of D. melanogaster

Byline: Bradley M. Hersh (a)(b), Craig E. Nelson (c), Samantha J. Stoll (a), Jason E. Norton (d), Thomas J. Albert (d), Sean B. Carroll (a) Keywords: Hox protein; Ultrabithorax; Drosophila; Wing; Haltere; Anachronism Abstract: Hox proteins have been proposed to act at multiple levels within regulatory hierarchies and to directly control the expression of a plethora of target genes. However, for any specific Hox protein or tissue, very few direct in vivo-regulated target genes have been identified. Here, we have identified target genes of the Hox protein Ultrabithorax (UBX), which modifies the genetic regulatory network of the wing to generate the haltere, a modified hindwing. We used whole-genome microarrays and custom arrays including all predicted transcription factors and signaling molecules in the Drosophila melanogaster genome to identify differentially expressed genes in wing and haltere imaginal discs. To elucidate the regulation of selected genes in more detail, we isolated cis-regulatory elements (CREs) for genes that were specifically expressed in either the wing disc or haltere disc. We demonstrate that UBX binds directly to sites in one element, and these sites are critical for activation in the haltere disc. These results indicate that haltere and metathoracic segment morphology is not achieved merely by turning off the wing and mesothoracic development programs, but rather specific genes must also be activated to form these structures. The evolution of haltere morphology involved changes in UBX-regulated target genes, both positive and negative, throughout the wing genetic regulatory network. Author Affiliation: (a) Howard Hughes Medical Institute and University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI 53703, USA (b) Clemson University, 132 Long Hall, Clemson, SC 29634, USA (c) University of Connecticut, 91 North Eagleville Road, Storrs, CT 06269, USA (d) NimbleGen Systems, Inc., 1 Science Ct., Madison, WI 53711, USA Article History: Received 8 September 2006; Revised 20 October 2006; Accepted 3 November 2006