Clathrin-mediated endocytosis is the best characterized process for the entry of proteins and lipids at the plasma membrane of eukaryotic cells. It is also the Achilles’ heel for human diseases such as neurodegenerative diseases and congenital myopathies. While neuronal axons form small clathrin-coated pits for fast endocytosis at synapses, muscle cells form large flat clathrin-coated plaques for cell adhesion at costameres, a cornerstone of mechanotransduction in muscle through their role as physical and functional links between the extracellular matrix and the cytoskeleton. We have demonstrated that the formation of actin networks capable of scaffolding intermediate filaments around clathrin plaques requires dynamin 2 (DNM2), another member of the endocytosis machinery crucial for the formation and release of clathrin-coated vesicles. Mutations in DNM2, amphiphysin 2 (BIN1) and myotubularin (MTM1) lead to centronuclear myopathy (CNM) and we showed that clathrin plaques are altered in CNM cells and mouse models. One common denominator in all three forms is a defective actin and cortical cytoskeleton leading to disorganized costameres, suggesting a defect of mechanotransduction as a common pathomechanism in CNMs. Our preliminary results strongly indicate that this alteration is associated with defective YAP/TAZ mechanosensitive pathway leading to altered transcription of their target genes. The first objective of CLASS is to decipher the function of clathrin plaques in YAP/TAZ mechanotransduction and to highlight involvement of this function in the pathomechanisms of centronuclear myopathy. We will (1) analyse clathrin plaque response to mechanical cues, (2) dissect mechanotransduction signaling in CNM and (3) reveal the benefit of releasing YAP/TAZ nuclear sequestration on CNM myotubes. While our results point towards a specialized function for clathrin plaques at muscle costameres, one fundamental question remains: Why do some cells exclusively form coated pits while others form plaques? We recently achieved the proof of concept that formation and plasticity of CCS are controlled by tissue-specific alternative splicing events through investigation of clathrin heavy chain's exon 31, which is aberrantly spliced in myotonic dystrophy (DM1), a "spliceopathy" affecting in particular muscle and central nervous system (CNS) functions. In DM1, functional loss of RNA binding proteins MBNL1 and CELF1 disturbs the developmentally regulated splicing program resulting in aberrant expression of embryonic isoforms in adult tissues. The second objective is to reveal the mechanisms by which muscle cells form plaques using alternative splicing isoforms of the endocytosis machinery and provide novel insight to DM1 pathophysiology. We will (4) reveal the effect of skipping key exons of developmentally regulated splicing variants of endocytosis proteins in neurons and myotubes, (5) decipher the effect of mis-regulated splicing of the endocytosis machinery in DM1 cells and (6) force exon skipping of developmentally regulated splicing variants in mice CLASS offers a genuinely innovative opportunity to push beyond the actual limitations concerning the fundamental biology of endocytosis: We will unravel how alternative splicing can modulate clathrin polymerization and induce formation of mechano-signaling platforms. This will be a major conceptual turning point in the endocytosis field by proving with unambiguous visual evidence that the clathrin machinery is genetically regulated to produce functional diversity. Our technical capabilities and leading expertise in the clathrin field, CNM and DM1 pathophysiology, our unique expertise in producing genetically modified hiPSC clones and differentiating them in neurons and muscle cells, and our powerful expertise on RNA splicing, put us in a unique position to undertake the dissection of genetic determinants in clathrin structural plasticity in healthy and diseased states.