The proposed experiments focus on the dally gene which encodes a GPI linked cell surface proteoglycan in Drosophila. Proteins in this class are thought to associate with growth factors and may function as co-receptors. The dally gene was initially identified in Drosophila because hypomorphic mutations caused a delay in certain mitotic division in the eye disc and in the lamina precursors of the brain. Associated with these cell cycle defects is a failure to repress G1 cyclins (A and possibly E) such that they persist into M phase. Selleck shows that reductions in cyclinA dosage partially rescues the mitotic arrest, suggesting that the dal phenotype is a consequence of this expression. In the present proposal, Selleck wishes to test a specific hypothesis, namely that dally acts as a co-receptor for the BMP like growth factor dpp and that local synthesis of that growth factor is what controls the pattern of division. Dally would therefore provide a unique handle on the role of Glypicans in the reception of growth factor signals. In addition to the production of antibodies to dally and the biochemical characterization of its cell surface linkage and structure function, most of the proposal focuses on the interaction between dal and the dpp pathway. Some of these studies will be carried out on the wing disc where downstream molecular marker for dpp reception (I. e., omb and sal gene) are available and have been well characterized. Others investigate whether simultaneous expression of dal alters a cell's sensitivity to ectopic dpp expression. Selleck will also continue his characterization of the relationship between dal and cell cycle regulators, particularly the mechanisms underlying the persistence of cyclin E in metaphase. Tests for direct physical interactions between dal and dpp will be carried out using radiolabeled dpp and the previously obtained antibodies to dal, or co-electrophoresis. Mutagenesis screens are proposed to obtain true null alleles of dal by screening in the presence of a duplication to counter the potential haplo-lethality of the locus.
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