Disparate expression specificities coded by a shared Hox-C enhancer.

Abstract

Can a single regulatory sequence be shared by two genes undergoing functional divergence? Here we describe a single promiscuous enhancer within the <i>Drosophila</i> Antennapedia Complex, EO053, that directs aspects of the expression of two adjacent genes, <i>pb</i> (a <i>Hox2</i> ortholog) and <i>zen2</i> (a divergent <i>Hox3</i> paralog), with disparate spatial and temporal expression patterns. We were unable to separate the <i>pb</i>-like and <i>zen2</i>-like specificities within EO053, and we identify sequences affecting both expression patterns. Importantly, genomic deletion experiments demonstrate that EO053 cooperates with additional <i>pb</i>- and <i>zen2</i>-specific enhancers to regulate the mRNA expression of both genes. We examine sequence conservation of EO053 within the Schizophora, and show that patterns of synteny between the <i>Hox2</i> and <i>Hox3</i> orthologs in Arthropods are consistent with a shared regulatory relationship extending prior to the <i>Hox3/zen</i> divergence. Thus, EO053 represents an example of two genes having evolved disparate outputs while utilizing this shared regulatory region. <b>Editorial note</b>: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).