For four decades, a single model governed how scientists understood the renewal of muscle cells at their most fundamental level — until now. Researchers at Emory University have discovered that actin filaments, the molecular scaffolding of muscle contraction, grow from the opposite end than biology long assumed, overturning a cornerstone principle of cell biology. The finding not only resolves a paradox that had quietly persisted since the 1980s, but illuminates why certain genetic mutations lead to dilated cardiomyopathy — a progressive failure of the heart's ability to do its most essential