<p> The type 1 transmembrane receptor tyrosine kinase (RTK), Neu/ErbB2 is a member of the Epidermal Growth Factor Receptor (EGFR) family that functions as a potent mediator of normal cell-growth and development. However, the aberrant expression of RTKs has also been implicated in many human cancers. For example, Neu over-expression has been implicated in human breast and ovarian cancers, and is correlated with poor clinical prognosis. At least one pTyr residue in Neu, Let-23, and PDGFR-B receptor tyrosine kinase is reported to have negative signaling capability. The intrinsic negative signaling behaviour of any of these pTyr residues, such as pTyr at 1028 of Neu (NeuYA) has yet to be fully exploited with a view to better understanding of RTK signaling, leading to more precise knowledge in human cancer development and disease treatment. </p> <p> Here we aimed to determine the role, specificity and the signaling pathway components of rat-NeuYA in Drosophila melanogaster. Specifically, we asked whether pTyr 1028 of Neu could affect signaling from heterologous RTKs. If so, what would be the pathway components? Are they already known or novel? Using a targeted misexpression system, such as the GAL4-Upstream Activating Sequence (GAL4-UAS) system, we generated graded phenotypes of various Neu alleles in adult Drosophila eye and wing tissues, suitable for dosage sensitive modifier screening. Taking the advantage of these graded phenotypes, we sought to identify and evaluate the signaling characteristics of Neu/ErbB2. NeuYA, in particular, suppressed the rough-eye phenotype of other 'add-back' Neu alleles, suggesting an inhibitory role in RTK signaling. The dosage sensitive modifier screen has also shown that the signal attenuating steps, such as receptor-mediated endocytosis, receptor recycling, and lysosomal degradation work in a YA-independent manner. To identify the components of the NeuYA signaling pathway in RTK signal attenuation, a genome-wide dominant modifier screen was undertaken to screen over 60,000 F1 progeny either for suppression or enhancement of the rough-eye phenotype of GMR-NeuYAE adults. Using deficiency mapping, we isolated and identified that one complementation group of suppressors to be alleles of lilliputian. Additionally, we narrowed down several groups of enhancers to certain deficiency regions, uncovering 10-30 genes- previously not known to the receptor tyrosine kinase signaling pathways. Collectively, here we report several novel NeuYA-interactors in RTK signal attenuation in Drosophila. </p> / Thesis / Doctor of Philosophy (PhD)