The question we wish to address in the proposed research is how microtubule composition affects the mechanical properties of cells, and how it influences cells’ reaction to external stretching forces. We will use the fruit fly stretch-responsive sensory organs called chordotonal organs as a model system to address this question. The chordotonal organs provide an excellent opportunity to address the correlation between microtubule composition and cell mechanics, as they harbor two different cell types, which contain different compositions of microtubules and react very differently to the stretching forces imposed on the organ. We have shown that reducing the level of certain tubulin isotypes in these cells by RNA-interference affect the differential pattern of cell elongation during organ stretching. We plan to genetically manipulate the microtubule composition in these two cell types and study the phenotypic consequences in three levels: 1. Ultrastructure of the cytoskeleton 2. mechanical properties of the cells 3. Organ morphogenesis. If clear correlation is found between specific tubulin isotypes and specific cellular properties (mainly mechanical properties), a mechanistic study will follow, focusing on Tau (mainly) and other microtubule associated proteins.