The sequential changes in the three-dimensional organization of the filamentous components of human platelets following surface activation were investigated in whole-mount preparations . Examination of intact and Triton-extracted platelets by high voltage electron microscopy provides morphological evidence of increased polymerization of actin into the filamentous form and an increased organization of the cytoskeletal elements after activation . The structure of resting platelets consists of the circumferential band of microtubules and a small number of microfilaments randomly arranged throughout a dense cytoplasmic matrix. Increased spreading is accompanied by cytoskeletal reorganization resulting in the development of distinct ultrastructural zones including the peripheral web, the outer filamentous zone, the "trabecular-like" inner filamentous zone, and the granulomere . These zones are present only in well-spread platelets during the late stages of surface activation and are retained following Triton extraction . Extraction of the less stable cytoplasmic components provides additional information about the underlying structure and filament interactions within each zone .The morphological transformation that accompanies platelet activation has been attributed to alterations involving both the distribution and the degree of polymerization of the various contractile and structural proteins within platelets. Contractile proteins have been implicated in many of the events ofactivation including centralization and secretion of granules, aggregation, and clot retraction (1,7,8,35,48). Recent biochemical studies of thrombin-induced platelet activation have demonstrated a time-dependent incorporation of actin into the filamentous form and an increase in the amount of myosin associated with the cytoskeleton (5, 20, 37). The organization of these platelet contractile proteins, particularly actin and myosin, has been studied at the light microscopic level through immunocytochemical techniques (9,11,12,33,35). These studies have indicated that there are temporal changes in the whole-cell distribution of actin and myosin within platelets. While they are initially uniformly distributed, actin and myosin are segregated to selective areas as spreading progresses. Other studies employing transmission THE JOURNAL OF CELL BIOLOGY " VOLUME 98 JUNE 1984 2019-2025 ® The Rockefeller University Press -0021-9525/84/06/2019/07 $1 .00 electron microscopy (TEM)' have yielded considerable information regarding the types of filaments within platelets and overall platelet structure (22,23,42,(44)(45)(46)(47)(48) . Only a very small part of the platelet cytoskeleton is visible in conventional TEM thin sections hindering an accurate determination of the overall three-dimensional organization and in situ relationships ofthe filamentous cytoskeletal elements. Wholemount preparations have therefore been increasingly utilized to study platelet ultrastructure (2,22,23,25,26,29,42). However, masking ofthe cytoskeletal elements by the exten...
Plasma fibronectin was measured in patients with breast cancer, colon cancer, and acute leukemia. In the patients with solid tumors, mean levels were significantly elevated above the mean level of age and sex‐matched normals whether the disease was thought to be metastatic or not (P < 0.001). It did not make a difference whether the determinations were done prior to or during chemotherapy. Fibronectin was measured serially in eight hospitalized patients with leukemia during intensive induction chemotherapy. Noramal concentrations were found prior to therapy. However, fibronectin concentration fell on the day following chemotherapy in nine of 12 episodes (P <0.05), and during sepsis in 13 of 13 episodes (P <0.001). Thus, the concentration was influenced by at least two factors: recent chemotherapy and sepsis. Because fibronectin concentration is sensitive to clinical events other than the status of the malignancy, it seems unsuitable as a tumor marker, at least as a single isolated measurement.
This report demonstrates a case of acute megakaryoblastic leukemia evolving in a patient with idiopathic myelofibrosis with myeloid metaplasia. A presumptive diagnosis was made by cytochemical stains, alpha-naphthyl acetate esterase, and alpha-naphthyl butyrate esterase. The diagnosis was established by electron microscopic platelet peroxidase studies of the peripheral blood blast cells and supported by flow cytometry and immunoalkaline phosphatase studies. Specific monoclonal antibodies directed against platelet glycoproteins Ib (6D1) and IIb/IIIa (10E5), which have not been described frequently in analyzing leukemia, were used for flow cytometry and direct immunoalkaline phosphatase technique. Cytogenetic studies demonstrated a deletion of the long arm of chromosome 6 with breakpoints at bands q15 and q23, and ring chromosome 6 (p25, q27). The diagnosis of megakaryoblastic leukemia requires accurate cytochemical stains, platelet peroxidase by electron microscopic examination, and studies employing specific monoclonal antibodies directed against platelets and megakaryoblasts. The exact origin of the circulating megakaryoblasts in these cases is not known and needs additional investigation.
We labeled surface glycoproteins of human platelets by the neuraminidase-galactose oxidase/borotritiide and the periodate/borotritiide methods. When labeled platelets were treated with 1-nM thrombin, a minor glycoprotein weighing 68,000–85,000-d was lost from the surface, and a soluble glycoprotein weighing 57,000- 68,000-d was found in the supernatant. Treatment of platelets with ADP, collagen, or the calcium ionophore A23187 did not cause loss of the 68,000–85,000-d glycoprotein from platelet surfaces or appearance of the 57,000–68,000-d glycoprotein in the supernatant. However, trace amounts of the intact 68,000–85,000-d glycoprotein were found in the supernatants of platelets that were not treated with thrombin. The numerous effects of thrombin on platelets could be initiated by cleavage and release the thrombin-sensitive glycoprotein.
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.
customersupport@researchsolutions.com
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.