Abstract. Fluorescently labeled alpha-actinin, isolated from chicken gizzards, breast muscle, or calf brains, was microinjected into cultured embryonic myotubes and cardiac myocytes where it was incorporated into the Z-bands of myofibrils. The localization in injected, living cells was confirmed by reacting permeabilized myotubes and cardiac myocytes with fluorescent alpha-actinin. Both living and permeabilized cells incorporated the alpha-actinin regardless of whether the alpha-actinin was isolated from nonmuscle, skeletal, or smooth muscle, or whether it was labeled with different fluorescent dyes. The living muscle cells could beat up to 5 d after injection. Rest-length sarcomeres in beating myotubes and cardiac myocytes were 1.9-2.4 um long, as measured by the separation of fluorescent bands of alpha-actinin. There were areas in nearly all beating cells, however, where narrow bands of alpha-actinin, spaced 0.3-1.5 ~m apart, were arranged in linear arrays giving the appearance of minisarcomeres. In myotubes, alpha-actinin was found exclusively in these closely spaced arrays for the first 2-3 d in culture. When the myotubes became contraction-competent, at ~day 4 to day 5 in culture, alpha-actinin was localized in Z-bands of fully formed sarcomeres, as well as in minisarcomeres. Video recordings of injected, spontaneously beating myotubes showed contracting myofibrils with 2.3 ~m sarcomeres adjacent to noncontracting fibers with finely spaced periodicities of alpha-actinin. Time sequences of the same living myotube over a 24-h period revealed that the spacings between the minisarcomeres increased from 0.9-1.3 to 1.6-2.3 #m. Embryonic cardiac myocytes usually contained contractile networks of fully formed sarcomeres together with noncontractile minisarcomeres in peripheral areas of the cytoplasm. In some cells, individual myofibrils with 1.9-2.3 #m sarcomeres were connected in series with minisarcomeres. Double labeling of cardiac myocytes and myotubes with alpha-actinin and a monoclonal antibody directed against adult chicken skeletal myosin showed that all fibers that contained alpha-actinin also contained skeletal muscle myosin. This was true whether alpha-actinin was present in Z-bands of fully formed sarcomeres or present in the closely spaced beads of minisarcomeres. We propose that the closely spaced beads containing alpha-actinin are nascent Z-bands that grow apart and associate laterally with neighboring arrays containing alpha-actinin to form sarcomeres during myofibrillogenesis.M YOFIBRIL formation in embryonic vertebrate skeletal and cardiac cells has been examined in a number of different ways. Biochemical data have shown there is coordinate synthesis of actin, myosin, tropomyosin, and alpha-actinin during vertebrate myogenesis (6). Immunocytochemical and electron microscopic data suggest that thick and thin filaments are formed at the same time in the cytoplasm and subsequently become organized into sarcomeric arrays (13, 18). The assumption in these studies (13,18) is that the filaments are the s...
Clinical histories, endoscopic ultrasound (EUS)-guided fine-needle aspiration (FNA) material, and immunohistochemical stains performed on cell block samples of 6 solid-pseudopapillary tumors of the pancreas (SPTPs) were reviewed in the cases of 5 females (13-58 years) and 1 man (57 years); all had abdominal pain. Preliminary cytologic diagnoses at endoscopy included 1 SPTP 2 low-grade neoplasms, and 3 pancreatic endocrine tumors. Variable numbers of branching fragments with central capillaries and myxoid stroma were seen in the smears of 5 of 6 cases but were more apparent in the cell block material of all cases. The cells had bland nuclear features and rare grooves. Extensive necrosis was noted in 1 case and rare mitotic figures in 1. SPTPs showed strong cellular immunoreactivity for vimentin and focal weak keratin reactivity. Neuron-specific enolase, alpha1-antitrypsin, and alpha1-antichymotrypsin stains performed in 2 cases were strongly positive. Subsequent surgical resection confirmed all diagnoses. EUS-guided FNA diagnosis of SPTP is accurate. The characteristic branching papillae with myxoid stroma are best seen in cell block slides. Clinical setting, cytomorphologic features, and immunostains of the cell block help distinguish SPTP from pancreatic endocrine tumors, acinar cell carcinoma, and papillary mucinous carcinoma.
Infliximab therapy was successful in a patient with sarcoidosis. Tumor necrosis factor-alpha may be an important mediator of clinical disease in sarcoidosis and could be an attractive target for therapeutic intervention. However, infliximab may cause adverse effects associated with cytokine cascade manipulation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.