A polarized actin cytoskeleton and its role in cortical patterning in early Drosophila embryos

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Cortical domains, i. e. apical, sub-apical, lateral and basal domains, are a characteristic feature of epithelial cells. While some proteins integrated or associated with the plasma membrane are uniformly distributed, others are restricted to specific so-called cortical domains. Cortical domains are an defining feature of epithelial cells, since they provide the template for localization of functionally important molecules after differentiation. Beside their importance in development and differentiation, the formation, change or loss of cortical patterning as part of an epithelial-mesenchymal transition are important steps in tumorigenesis and are thus of great medical relevance. Although multiple mechanism for the initial segregation and maintenance of the distribution of proteins and protein complexes to specific cortical domains have been previously identified in a variety of experimental systems, a conclusive and unifying view is missing. Here we analyse the emergence of the sub apical domain during early Drosophila embryogenesis. In the proposed project, we will test the novel model that polarised cortical actin leads to restriction of sub apical determinants during the transition from syncytial to cellular development. Specifically we will develop assays for labelling the (+)-ends of F-actin, visualisation of cortical actin and address the function of the formin Dia, the motor protein Myo II and the microtubule motor Kinesin-1.