Structural and Proteomic Analysis of the Drosophila Cardiac Tube

Abstract

Drosophila melanogaster possess a simple linear heart tube which is an efficient in vivo system for studying basic developmental and physiological processes as well as for investigating potentially conserved pathogenic mechanisms of genetically inherited cardiac disorders. Human cardiomyopathies commonly arise from cytoarchitectural mutations. We previously showed that, as in humans, Drosophila exhibit disparate cardiac responses to depressed or enhanced myosin biomechanical properties. Here, we further characterized the morphological and ultrastructural consequences of altered myosin function on the Drosophila heart. Fluorescent microscopy revealed D45 flies, expressing myosin with depressed ATPase and in vitro sliding properties, show cardiac dilation with relatively normal myofibrillar organization. However, Mhc5 fly hearts, expressing myosin with enhanced molecular properties show centrally located restricted regions, a loss of contractile material and myofibrillar disarray. Moreover, electron microscopy revealed perturbed sarcomeric organization of the cardiomyocytes in both mutants. Mitochondria appeared swollen with apparent increased matrix volume and membranic rupture resulting in a prevalence of vacuolization. These cardiac phenotypes bear similarity to those observed in human cardiomyopathies and imply the existence of conserved pathological responses to altered myosin motor function. To further substantiate the use of the Drosophila heart as a model for investigating developmental, physiological and pathological processes and to identify conserved and potentially unique molecular components, we have undertaken preliminary proteomic analysis of isolated hearts. LC-MS/MS analysis identified ∼450 proteins with high confidence. The cardiac proteins derive primarily from the sarcomere, cytoskeleton and the mitochondria. Many of the major cardiac components appear conserved between flies and humans. We ultimately seek to use quantitative proteomic studies to identify how specific lesions of myosin perturb protein networks within the Drosophila heart, and to determine how these perturbations contribute to the pathogenesis of cardiomyopathy.