Uncovering the DNA Binding Diversity of the Six Family of Transcription Factors in Drosophila melanogaster and Heliconius erato

Abstract

Transcription factor (TF) DNA-bindning specificity is determined by how their DNA-binding domain interacts with DNA. DBDs are highly conserved and used to classify TF into families. Members of a family usually recognized the same binding motif, but small changes in the DBD can lead to diversification in binding specificity. TFs members of the sine oculis homeobox (SIX) family are found from sponges to humans and are consider atypical members of the homeodomain family. They regulate numerous phenotypic features spanning from eye development in flies to red color pattering in the Heliconius butterflies wings. How evolutionary related TFs DNA-binding specificity diversifies is not fully understood. Using full length SIX proteins (Sine Oculis, SIX4 and Optix) from Drosophila melanogaster and Heliconius erato, we have performed in vitro Systematic Evolution of Ligands by Exponential Enrichment (SELEX-seq) to identify the DNA binding specificity, between the SIX TFs orthologs. Our preliminary data has shown that they bind to their canonical binding motif (TGATAC), however the way they bind can be different. Our data shows that optix from Heliconius, can bind both as a monomer and a homodimer with preferred 3-bp spacing between binding sites. In contrast to Heliconius optix, the ortholog from Drosophila prefers a GA flank 5’ to the core motif. Currently we are working with our data to provide new insights in the binding diversity of the SIX TFs, allowing us to predict the genomic targets of the SIX genes in both Drosophila melanogaster and Heliconius erato.