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

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.

Targeted deletion of the suppressor gene bin1/amphiphysin2 accentuates the neoplastic character of transformed mouse fibroblasts

“…Mixed 129sv/BL6 mice heterozygous for the Bin1 null allele 16 were mated to heterozygous p53 null, B6 mice (C7BL/6J, Jackson Laboratories) and offspring from this mating were interbred to generate embyros that were heterozygous or homozygous for each gene. p53 is a key suppressor of c-myc, so to assess the contributions of Bin1 as a suppressor of c-myc we wished to focus solely on the p53-independent effects of Bin1.…”

“…Notably, the benefit of Bin1 loss to cell growth and survival appears to be contingent on cell transformation. [13][14][15][16] Taken together, these studies suggest that Bin1 may restrain cellular proliferation and survival in a contextual manner that is dependent on some feature of neoplastic pathophysiology.…”

“…Amphiphysin2) associate with endocytotic complexes, however, gene knockout studies in mouse, Drosophila, and fission yeast indicate that Bin1 is nonessential for endocytosis. 16,[19][20][21] Instead, recent studies suggest that this association may reflect some role in trafficking processes. 22,23 In yeast, genetic studies of the conserved BAR adapter proteins (homologs of mammalian Bin1/Amphiphysin2 and Bin3) highlight connections to actin control and stress signaling.…”

“…29 Thus, some BAR adapter proteins may link trafficking processes to transcription or other nuclear events in a manner that has yet to be fully appreciated. In this study, we exploited a recently developed knockout mouse model 16 to probe the hypothesized anti-proliferative role of Bin1 in c-myc-transformed cells.…”

Cardiac BIN1 (cBIN1) is a regulator of cardiac contractile function and an emerging biomarker of heart muscle health

“…The role of BIN1 in mechanistic HF progression was first noted when constitutive Bin1 knockout mice died of perinatal lethal cardiomyopathy (Muller et al, 2003). Later, a decrease in BIN1 transcription was identified in acquired human HF and multiple animal models of HF (Lyon et al, 2012;Caldwell et al, 2014), which recovers during functional recovery (Lyon et al, 2012).…”