The kidney filter contains a unique assembly of podocyte epithelial cells that tightly enwrap the glomerular capillaries with their foot processes and the interposed slit diaphragms. Identification of mutations in genes encoding NEPHRIN and other slit diaphragm (SD) proteins causing familial nephrotic syndrome has significantly contributed to the molecular understanding of the glomerular filter, and the podocyte SD has become a major focus in the research of hereditary kidney diseases. NEPH1-3 and NEPHRIN are type I transmembrane molecules of the immunoglobulin superfamily that are believed to form the core complex of the SD, and are anchored in the podocyte plasma membrane. However, the concept of a NEPHRIN-based slit diaphragm is challenged by the recent observation that entire classes of animals (e.g. birds and reptiles) are forming SDs despite lacking NPHS1 homologues in their genomes. More importantly, through the difficult accessibility of podocytes in vivo and the lack of conditional alleles for the genes encoding Nphs1, Neph1, Neph2 and Neph3, the precise function and molecular composition of the SD has still not been resolved. The major goal of this study is to unravel the molecular architecture of the SD. For this purpose, we established a multispecies platform of complementary transgenic mice with floxed genes for Nphs1, Neph1, Neph2 and Neph3, as well as Gallus gallus and Drosophila model systems that will be combined with high-resolution, large-scale serial 3D EM reconstructions and functional studies. This will provide the foundation to: (1) Correlate the high-resolution 3D structure of SDs being formed in animal species containing (e.g. mice) or missing (e.g. chicken) Nphs1 in their genomes, allowing to assess the impact of Nphs1 on the SD ultrastructure. (2) Analyze the precise role of all Neph-Nephrin family members for the development, stability, dynamics and maintenance of the SD by using podocyte specific- and timely inducible KO models of the respective genes, and (3) Systematically decode the global signaling network of the Neph-Nephrin complex by using a genome-wide RNAi suppressor screen in Drosophila nephrocytes. Collectively, our results will offer a comprehensive insight into the structure and function of the slit diaphragm as prerequisite for therapeutic approaches to ameliorate hereditary or acquired glomerular diseases.