Pattern Formation in the Drosophila Eye Disc

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Treisman 9728140 The Drosophila eye consists of a highly ordered array of identical sub-units, each containing a defined set of photoreceptors. Photoreceptor differentiation begins at the posterior margin of the larval eye imaginal disc and gradually progresses anteriorly, in a process which requires the activity of hedgehog (hh) protein secreted by the differentiated photoreceptors. The initiation of differentiation is driven by the TGF-Beta family member decapentaplegic (dpp), which is expressed at the posterior and lateral margins of the eye disc. The inhibitory effect of the Wnt family member wingless (wg), present at the lateral margins, restricts initiation to the posterior margin. The mechanisms by which wg inhibits the function of dpp laterally and dpp prevents the expression of wg posteriorly are not understood. Dr. Treisman proposes to determine the molecular basis for their effects on each other by studying the effects of loss of function or ectopic activity of components of the dpp and wg signaling pathways. She will then investigate whether dpp and wg are regulated by, and mediate the effects of, five genes that are required for eye formation. She has also conducted a screen for new mutations affecting the size and shape of the eye, which may affect genes required for eye disc specification or patterning. This screen was done by making clones of homozygous mutant cells in the eyes of phenotypically wild type heterozygous flies, allowing us to examine the role in eye development of genes that are also required in the embryo. Dr. Treisman plans to characterize these mutations and clone the novel genes that are required for cells in the eye disc to develop as retinal tissue. The observed structural and functional homology between the Pax-6 proteins encoded by Drosophila eyeless, mouse Small eye and human Aniridia confirms the similarity of the basic mechanisms underlying eye development in flies and vertebrates. This research is expected to identify novel molecules which are li kely to function in the development of vertebrates as well as of Drosophila.