Template Properties of 5-Methyl-2'-Deoxycytidine and 5-Hydroxymethyl-2'-Deoxycytidine in Reactions with Human Translesion and Reparative DNA Polymerases

Molecular Biology - 5-Methyl-2'-deoxycytidine (mC) and the product of its controlled oxidation, 5-hydroxymethyl-2'-cytidine (hmC), play a key role in the epigenetic regulation of gene...     

Haemorrhage as a Complication of Extracorporeal Pig Liver Perfusion: Studies on Mechanism and Prevention

The use of extracorporeal pig liver perfusion for temporary liver support has been followed not infrequently by major bleeding with a fall in coagulation factors and platelets, rather than a rise as hoped. In 18 experimental perfusions in which ¹²⁵I-labelled fibrinogen was used as a marker there was in every instance a significant loss of the fibrinogen into the fluid supporting the liver in the perfusion chamber. Further, in 11 of the perfusions there was an additional loss into liver substance, this being associated with a very rapid fall in ¹²⁵I fibrinogen and platelets content of the perfusion fluid. Damage to the sinusoids from ischaemic damage incurred during removal of the liver could explain both the direct loss of fibrinogen and, as a result of intravascular coagulation, the associated loss within the perfused liver. No correlation could be found with biochemical function, but it proved possible to assess haematological safety before connexion of the patient to the perfusion by a shortened ¹²⁵I fibrinogen test. This was done in three patients treated by five perfusions and in none was the thrombocytopenia or coagulation disturbance adversely affected.     

Distinction between Infection and Rejection in Lung Transplantation

In distinguishing between infection and rejection after human lung transplantation clinical and radiological features were unhelpful, and even confusing. However, incipient rejection could be predicted and distinguished from infection by monitoring alterations in lymphocyte activity by the rosette inhibition test. Earlier prediction seems possible by detecting circulating lung-binding antibody. The ability to detect changes in the immunological status of a patient, even before clinical deterioration, has fundamental implications for the management of patients after transplantation.     

Fine needle aspiration cytology of malignant mesothelioma

The results of fine needle aspiration (FNA) cytology in 19 cases of malignant mesothelioma are presented. Adequate material for a diagnosis of malignancy was obtained in 17 cases, and in 8 cases a specific diagnosis of mesothelioma could be made. In four other cases, the findings were either consistent with or suggestive of mesothelioma; in four, accurate distinction from other neoplasms was not possible, and in two cases, adenocarcinoma was suggested. The spectrum of cytologic findings ranged from neoplasms of purely epithelial appearance through more pleomorphic biphasic neoplasms to anaplastic tumors. A combination of epithelial-like cell clusters, pavement-like sheets of epithelial cells with well-defined cell borders and prominent cell separation, dispersed angular cells with dense cytoplasm and some spindle-cell forms was the most specific cytologic pattern for mesothelioma. In four neoplasms, ultrastructural examination of aspirated material provided the additional evidence for a definitive diagnosis. The identification of hyaluronic acid within intracytoplasmic vacuoles, either in smears or in cell blocks, confirmed the diagnosis in three tumors. Only in one case, with a strong clinical background suggesting mesothelioma, was the cytologic preparation sufficient for diagnosis without ancillary diagnostic methods. FNA is of particular value in the diagnosis of pleural mesothelioma in patients who do not present with a pleural effusion. Obtaining material for cell block preparations, cytochemistry or ultrastructural study is generally necessary for definitive tumor typing.     

Cytologic and tissue culture characteristics of asbestos-induced mesothelioma in rats

Mesotheliomas were induced in rats by the intrapleural injection of Western Australia crocidolite asbestos. Over a two-year period, 10 of 18 animals in which implants were established developed mesotheliomas, for a 56% success rate. Histologically, most mesotheliomas were biphasic although predominantly spindle celled. Pleural fluid was examined in five of these malignant cases: three had a papillary epithelial picture, one had mainly anaplastic cells, and one contained predominantly spindle-shaped cells. Three types of cell aggregates occurred: classical collagen-containing papillary clusters, spindle-cell aggregates and cystlike spheres. These last structures corresponded to microcystic or adenomatoid growth present in four mesotheliomas. Two of the effusions were cultured successfully; the growth pattern was typically mesothelial, with in vitro production of collagen. Ultrastructurally, long, slender microvilli, cell junctions and intermediate filaments confirmed the mesothelial nature of these asbestos-induced rat malignancies.     

α-Antitrypsin Deficiency and Neonatal Hepatitis

Five out of 28 infants investigated in a regional survey of neonatal hepatitis were found to have genetically-determined deficiency of α₁-antitrypsin (ZZ phenotype). The clinical course and pathological changes varied considerably. All five infants had an acute hepatitis-like illness, and although this subsided cirrhosis later developed in three cases. The remaining two infants had minimal abnormalities of the liver function tests at 12 and 18 months of age, and one had increased hepatic fibrosis. Australia antigen was found in the serum of three infants, and Australia antigen or antibody in one or both parents of these and of one further case whose serum was negative. It is suggested that the association of neonatal hepatitis with α₁-antitrypsin deficiency may be commoner than previously realized and that Australia antigen acts as a trigger factor in these cases.     

Noncanonical prokaryotic X family DNA polymerases lack polymerase activity and act as exonucleases

The X family polymerases (PolXs) are specialized DNA polymerases that are found in all domains of life. While the main representatives of eukaryotic PolXs, which have dedicated functions in DNA repair, were studied in much detail, the functions and diversity of prokaryotic PolXs have remained largely unexplored. Here, by combining a comprehensive bioinformatic analysis of prokaryotic PolXs and biochemical experiments involving selected recombinant enzymes, we reveal a previously unrecognized group of PolXs that seem to be lacking DNA polymerase activity. The noncanonical PolXs contain substitutions of the key catalytic residues and deletions in their polymerase and dNTP binding sites in the palm and fingers domains, but contain functional nuclease domains, similar to canonical PolXs. We demonstrate that representative noncanonical PolXs from the Deinococcus genus are indeed inactive as DNA polymerases but are highly efficient as 3′-5′ exonucleases. We show that both canonical and noncanonical PolXs are often encoded together with the components of the non-homologous end joining pathway and may therefore participate in double-strand break repair, suggesting an evolutionary conservation of this PolX function. This is a remarkable example of polymerases that have lost their main polymerase activity, but retain accessory functions in DNA processing and repair.