Targeted Disruption of the Murine Bin1/Amphiphysin II Gene Does Not Disable Endocytosis but Results in Embryonic Cardiomyopathy with Aberrant Myofibril Formation

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Abstract
The mammalian Bin1/Amphiphysin II gene encodes an assortment of alternatively spliced adapter proteins that exhibit markedly divergent expression and subcellular localization profiles. Bin1 proteins have been implicated in a variety of different cellular processes, including endocytosis, actin cytoskeletal organization, transcription, and stress responses. To gain insight into the physiological functions of the Bin1 gene, we have disrupted it by homologous recombination in the mouse. Bin1 loss had no discernible impact on either endocytosis or phagocytosis in mouse embryo-derived fibroblasts and macrophages, respectively. Similarly, actin cytoskeletal organization, proliferation, and apoptosis in embryo fibroblasts were all unaffected by Bin1 loss. In vivo, however, Bin1 loss resulted in perinatal lethality. Bin1 has been reported to affect muscle cell differentiation and T-tubule formation. No striking histological abnormalities were evident in skeletal muscle of Bin1 null embryos, but severe ventricular cardiomyopathy was observed in these embryos. Ultrastructurally, myofibrils in ventricular cardiomyocytes of Bin1 null embryos were severely disorganized. These results define a developmentally critical role for the Bin1 gene in cardiac muscle development.