The tilt (tt) mutation of Drosophila melanogaster maps to the cis-regulatory region of the Iroquois Complex (Iro-C) located in the sosondowah (sowah) gene

The <i>tilt</i> ( <i>tt</i> ) mutation first described by Morgan and Bridges in 1915 has adult visible phenotypes in wing posture and vein formation. We have mapped <i>tt</i> to a genomic region within the <i>sosondowah</i> ( <i>sowah</i> ) gene that houses the cis-regulatory elements that control expression of the Iroquois Complex genes <i>araucan</i> ( <i>ara</i> ) and <i>caup olican</i> ( <i>caup</i> ) in the wing hinge and wing veins. Sequence analysis of the <i>tt¹</i> allele has identified a gtwin retrotransposon containing su(Hw) insulator binding sites within this region of <i>sowah</i> . We find that mutations in <i>su(Hw)</i> suppress the <i>tilt</i> phenotype, providing a potential mechanism for the insertion to affect the function of the Iroquois Complex.