Functional analysis of the septate junction protein complex in Drosophila melanogaster

Body cavities and external surfaces of metazoic organisms are covered with sheets of epithelial cells that act as physical and chemical barriers. Epithelial tissues divide the body into differentiated compartments with different chemical properties providing the barrier function in the trachea and lung, the blood brain barrier in the central nervous system and a powerful shield against pathogens and bacteria. In invertebrates the so- called septate junctions (SJs) mediate the barrier forming structures of epithelial cells. SJs are localized apicolaterally and consist of a highly stable and immobile core complex as well as core complex associated SJ proteins. The first part of this thesis investigates the protein domains of the claudin Megatrachea (Mega), an essential component of the SJ core complex in Drosophila melanogaster. The generation of various synthetic mega mutants under the endogenous promotor of mega gives new insights on essential Mega domains for in vivo function and stability. Amino acid deletions or exchanges lead to wild-type protein function, impaired protein trafficking, affected protein localization, defects in tracheal morphology, impaired barrier function and unusual exocytosis. In the second part of this thesis the novel bicistronic gene würmchen (wrm) was identified and characterized. wrm is expressed in ectodermally derived tissues during embryogenesis, including epidermis, trachea and hindgut. wrm encodes the two transmembrane domain proteins Wrm1 and Wrm2, which both are essential for tracheal development. Wrm1 represents a SJ core component and is required for SJ morphology, epithelial barrier function and tracheal system morphogenesis. Wrm2 is essential for tracheal development during larval stages and represents a genuine or a transiently associated SJ component