Drosophila SAP18, a member of the Sin3/Rpd3 histone deacetylase complex, interacts with Bicoid and inhibits its activity

Bicoid directs anterior development in Drosophila embryos by activating dif ferent genes along the anterior-posterior axis. However, its activity is do wnregulated at the anterior tip of the embryo, in a process known as retrac tion. Retraction is under the control of the terminal polarity system, and results in localized repression of Bicoid target genes. Here, we describe a Drosophila homolog of human SAP18, a member of the Sin3A/Rpd3 histone deac etylase complex, dSAP18 interacts with Bicoid in yeast and in vitro, and is expressed early in development coincident with Bicoid. In tissue culture c ells, dSAP18 inhibits the ability of Bicoid to activate reporter genes. The se results suggest a model in which dSAP18 interacts with Bicoid to silence expression of Bicoid target genes in the anterior tip of the embryo.