Cytochemical localization of calcium in prefusion myoblasts from the chick embryo myotome

Increased calcium deposits and decreased Ca2+-ATPase in right ventricular myocardium of ascitic broiler chickens

Right ventricular hypertrophy and failure is an important step in the development of ascites syndrome (AS) in broiler chickens. Cytoplasmic calcium concentration is a major regulator of cardiac contractile function and various physiological processes in cardiac muscle cells. The purpose of this study was to measure the right ventricular pressure and investigate the precise ultrastructural location of Ca(2+) and Ca(2+)-ATPase in the right ventricular myocardium of chickens with AS induced by low ambient temperature. The results showed that the right ventricular diastolic pressure of ascitic broilers was significantly higher than that of control broilers (P < 0.01), and the maximum change ratio of right intraventricular pressure (RV +/- dp/dt(max)) of ascitic broilers was significantly lower than that of the controls (P < 0.01). Extensively increased calcium deposits were observed in the right ventricular myocardium of ascitic broilers, whereas in the age-matched control broilers, calcium deposits were much less. The Ca(2+)-ATPase reactive products were obviously found on the sarcoplasmic reticulum and mitochondrial membrane of the control right ventricular myocardium, but rarely observed in the ascitic broilers. The data suggest that in ascitic broilers there is the right ventricular diastolic dysfunction, in which the overload of intracellular calcium and the decreased Ca(2+)-ATPase activity might be the important factors.

Epithelial-mesenchymal transitions: a mesodermal cell strategy for evolutive innovation in Metazoans

Epithelial-mesenchymal transitions (EMTs) are well known processes in which new mesenchyme is locally generated from epithelia. During the development of the vertebrate embryo, EMTs are a source of mesenchyme in diverse places and stages through embryonic morphogenesis, especially in mesodermal domains. In the present work we consider the embryo as a two-state system in which epithelium and mesenchyme represent the stable and unstable states, respectively. We think that a pattern of recurrent oscillations between the plasticity and exploratory behaviour of the mesenchyme and the stability of the epithelia can be recognized in the embryogenesis of vertebrates and, probably, in most tripoblastic Metazoans. Mesoderm, in particular, might be regarded as a cell layer able to oscillate between epithelial and mesenchymal states. The cellular and molecular mechanisms that enable these recurrent oscillations between stable (epithelial) and unstable (mesenchymal) states during embryogenesis provide the mesoderm with a large plasticity, an extended potential for innovation, and a better control of the three-dimensional (3D) body organization. In this scenario, it is conceivable that the origin of the mesoderm itself might be related to ancestral mechanisms regulating cell adhesion and detachment. We conclude that EMTs played a key role in the evolution of Metazoans, and are involved in the pathological and reparative processes of adult organisms.

Calcium-sensitive phospholipid binding properties of normal and mutant ferlin C2 domains

Mutations in dysferlin, a novel membrane protein of unknown function, lead to muscular dystrophy. Myoferlin is highly homologous to dysferlin and like dysferlin is a plasma membrane protein with six C2 domains highly expressed in muscle. C2 domains are found in a variety of membrane-associated proteins where they have been implicated in calcium, phospholipid, and protein-binding. We investigated the pattern of dysferlin and myoferlin expression in a cell culture model of muscle development and found that dysferlin is expressed in mature myotubes. In contrast, myoferlin is highly expressed in elongated "prefusion" myoblasts and is decreased in mature myotubes where dysferlin expression is greatest. We tested ferlin C2 domains for their ability to bind phospholipid in a calcium-sensitive manner. We found that C2A, the first C2 domain of dysferlin and myoferlin, bound 50% phosphatidylserine and that phospholipid binding was regulated by calcium concentration. A dysferlin point mutation responsible for muscular dystrophy was engineered into the dysferlin C2A domain and demonstrated reduced calcium-sensitive phospholipid binding. Based on these data, we propose a mechanism for muscular dystrophy in which calcium-regulated phospholipid binding is abnormal, leading to defective maintenance and repair of muscle membranes.