Identification of a novel downstream single-minded midline regulatory element in Drosophila melanogaster

Development of the <i>Drosophila melanogaster</i> central nervous system midline depends on the gene <i>single-minded</i> ( <i>sim</i> ). Although <i>sim</i> regulation has been studied extensively, the fact that an enhancer mediating late embryonic <i>sim</i> transcription has not been identified suggests that additional regulatory sequences remain unknown. We tested several evolutionarily conserved sequences in the <i>sim</i> downstream region and isolated <i>sim_3pB</i> , whose midline activity in a reporter gene assay begins later than previously characterized <i>sim</i> enhancers. Its activity shares several key similarities with the <i>Aedes aegypti sim</i> _ <i>5P3</i> enhancer, though is sufficiently different to warrant further investigation into how <i>sim_3pB</i> functions in its native context.