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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. [ABSTRACT FROM AUTHOR]

Pax6 genes encode transcription factors with two DNA-binding domains that are highly conserved during evolution. In Drosophila, two Pax6 genes function in a pathway in which twin of eyeless (toy) directly regulates eyeless (ey), which is necessary for initiating the eye developmental pathway. To investigate the gene duplication of Pax6 that occurred in holometabolous insects like Drosophila and silkworm, we used different truncated forms of toy and small eyes (sey), and tested their capacity to induce ectopic eye development in an ey-independent manner. Even though the Paired domains of TOY and SEY have DNA-binding properties that differ from those of the Paired domain of EY, they all are capable of inducing ectopic eye development in an ey mutant background. We also show that one of the main functional differences between toy and ey lies in the C-terminal region of their protein products, implying differences in their transactivation potential. Furthermore, we show that only the homeodomain (HD) of EY is able to downregulate the expression of Distal-less (Dll), a feature that is required during endogenous eye development. These results suggest distinct functions of the two DNA-binding domains of TOY and EY, and significant evolutionary divergence between the two Drosophila Pax6 genes. [ABSTRACT FROM AUTHOR]