Identification of functional sine oculis motifs in the autoregulatory element of its own gene, in the eyeless enhancer and in the signalling gene hedgehog

In Drosophila , the sine oculis ( so ) gene is important for the development of the entire visual system, including Bolwig's organ, compound eyes and ocelli. Together with twin of eyeless , eyeless , eyes absent and dachshund , so belongs to a network of genes that by complex interactions initiate eye development. Although much is known about the genetic interactions of the genes belonging to this retinal determination network, only a few such regulatory interactions have been analysed down to the level of DNA-protein interactions. Previous work in our laboratory identified an eye/ocellus specific enhancer of the sine oculis gene that is directly regulated by eyeless and twin of eyeless . We further characterized this regulatory element and identified a minimal enhancer fragment of so that sets up an autoregulatory feedback loop crucial for proper ocelli development. By systematic analysis of the DNA-binding specificity of so we identified the most important nucleotides for this interaction. Using the emerging consensus sequence for SO-DNA binding we performed a genome-wide search and have thereby been able to identify eyeless as well as the signalling gene hedgehog as putative targets of so . Our results strengthen the general assumption that feedback loops among the genes of the retinal determination network are crucial for proper development of eyes and ocelli.