<p> The proper organization of receptors and signal transduction protein complexes of epithelial and neuronal cells is crucial in tissue formation, cellular differentiation and proper overall development and function. Scaffolding proteins are major components involved in protein targeting and protein complex assembly. MAGUK.s, a family of scaffolding proteins with multiple binding domains such as PDZ, SH3 and GUK, are important regulators of cellular polarity by recruiting and assembling signal and cytoskeletal components into large complexes. Cell polarity is established and maintained by the proper formation and placement of cellular junctions, which separate the plasma membrane into two distinct domains: apical and basolateral. Epithelial polarity determinants from the Bazooka, Crumbs and Scribble complexes establish the boundaries between the apical and basolateral membrane domains and situate the adherens junctions (AJ) at the interface between the two domains. In neuronal cells, the organization and polarization of the presynaptic and the postsynaptic membranes is organized by the CASKIVELIIMINTl/Xllalpha complex. Both CASK and VELI also play a role in epithelial cells. </p> <p> Two novel proteins, originally discovered by Far Western overlay assay in Mus musculus, have been identified as additional binding partners of VELI: PALS I and PALS2. Both proteins are MAGUK.s and are thought to compete with CASK for binding VELI via L27 domain dimerization. PALSl, a major component of the Crumbs complex, is essential for the formation of AJ and the establishment of cellular polarity. PALS2 has been shown to co localize with E-cadherin below tight junctions and directly associate with nectin-like molecule-2 (Necl-2) at extra junctional regions, however its function remains unknown. </p> <p> Using Drosophila melanogaster as a model organism, we have identified the potential Drosophila ortholog of P ALS2, termed dP ALS2, and found that it is conserved across other species. We have done extensive sequence analysis of dP ALS2 at the nucleotide and amino acid level and determined the RNA transcript distribution and protein localization. </p> <p> dP ALS2 expression begins around stage 13 in embryonic tissues in a transversestriped pattern in the epithelia and continues in this striped pattern until the end of stage 17. dP ALS2 is expressed in adult tissues but undetectable in larval tissues. Based on homology and the expression pattern, dP ALS2 may play a role in cell adhesion or cell polarity, similar to the mammalian orthologs. However the striped expression pattern of dPALS2 is similar to segment polarity proteins thus implying dPALS2 may play a role in segment polarity. </p> / Thesis / Master of Science (MSc)