THE LINES GENE OF DROSOPHILA IS REQUIRED FOR SPECIFIC FUNCTIONS OF THE ABDOMINAL-B HOX PROTEIN

The Hox genes encode homeobox transcription factors that control the f ormation of segment specific structures in the anterior-posterior axis . HOX proteins regulate the transcription of downstream targets acting both as repressors and as activators. Due to the similarity of their homeoboxes it is likely that much of the specificity of HOX proteins i s determined by interaction with transcriptional cofactors, but few HO X cofactor proteins have yet been described. Here I present genetic ev idence showing that lines, a segment polarity gene of Drosophila, is r equired for the function of the Abdominal-B protein. In lines mutant e mbryos Abdominal-B protein expression is normal but incapable of promo ting its normal functions: formation of the posterior spiracles and sp ecification of an eighth abdominal denticle belt. These defects arise because in lines mutant embryos the Abdominal-B protein cannot activat e its direct target empty spiracles or other downstream genes while it can function as a repressor of Ultrabithorax and abdominal-A. The lin es gene seems to be required exclusively for Abdominal-B but not for t he function of other Hox genes.