Ability of a T-antigen transport-defective mutant of simian virus 40 to immortalize primary cells and to complement polyomavirus middle T in tumorigenesis.

The oncogenic potential of polyomavirus in newborn rats could not be expressed by a genome encoding only the middle T antigen but required the presence of one of the other two viral early genes, small T or large T. The tumorigenicity defect could also be complemented by other viral or cellular genes that are known to be implicated in immortalization and establishment functions. The simian virus 40(cT)-3 mutant (R. E. Lanford and J. S. Butel, Cell 37:801-813, 1984), which fails to localize to the nucleus, has the capacity to complement polyomavirus middle T in tumorigenesis and to immortalize primary rat embryo fibroblasts when it was cotransfected in the presence of pSV2-neo. Our data suggested that under the conditions of DNA-mediated tumor induction and cotransfection with a dominant selection marker, the cellular alterations achieved by nonnuclear oncogenes such as polyomavirus small T and simian virus 40(cT)-3 were sufficient to complement polyomavirus middle T in transformation and tumorigenesis.     

Resistance to H-2-restricted but not to allo-H2-specific graft and cytotoxic T lymphocyte responses in lymphoma mutant

The lymphoma mutant RMA-S escaped graft rejection after transplantation over a minor histocompatibility barrier, whereas it was rejected in H-2 allogeneic mice. The parental control line was rejected in both situations. The mutant, which had been selected against MHC class I molecules retained 5 to 10% of the wild-type H-2Db, Kb, and beta 2-microglobulin expression on the cell surface. It remained sensitive to allo-H-2b CTL in vitro, but was completely resistant to minor histocompatibility antigen-specific, H-2b-restricted CTL. It was equally resistant to other H-2b-restricted responses against internally derived Ag, such as tumor-specific CTL or a CTL clone specific for the influenza virus nucleoprotein. The results indicate a target cell defect that selectively abolishes the sensitivity to H-2-restricted CTL directed against internally processed Ag. This appears sufficient to shift the transplantation response over a minor histocompatibility Ag barrier from rejection to acceptance. There are two possible explanations for the results: 1) a block in the MHC class I-directed pathway for internal Ag processing, and 2) subthreshold H-2/Ag ligand density in relation to triggering requirements of restricted CTL. Regardless of the type of defect, the results demonstrate a difference between allo-H-2-specific and H-2-restricted CTL recognition at the level of the target cell.     

Intrachromosomal recombination mediated by papovavirus large T antigens.

To investigate the mechanism by which the large T antigen (T-Ag) of polyomavirus and simian virus 40 can promote recombination in mammalian cells, we analyzed homologous recombination events occurring between two defective copies of the polyomavirus middle T (pmt) oncogene lying in close proximity on the same chromosome in a rat cell line. Reconstitution of a functional pmt gene by spontaneous recombination occurred at a rate of about 2 x 10(-7) per cell generation. Introduction of the polyomavirus large T (plt) oncogene into the cell line by DNA transfection promoted recombination very efficiently, with rates in the range of 10(-1) to 10(-2) per cell generation. Recombination was independent of any amplification of viral sequences and could even be promoted by the large T-Ag from simian virus 40, which cannot activate polyomavirus DNA replication. To explain the role of large T-Ag, we propose a novel mechanism of nonconservative recombination involving slipped-strand mispairing between the two viral repeats followed by gap repair synthesis.     

Chronostratigraphie de la fin de la derniere glaciation,a la lumiere des resultats de l'etude lithostratigraphique et palynologique du site de Maisieres-Canal (Belgique)

The upper part of the palaeoclimatic sequence of Maisières-Canal shows a succession of four mild episodes at thetransition between the Pleniglacial and the Late-Glacial. Those four mild fluctuations are respectively correlated with Langerie, Lascaux, Angles-sur-l'Anglin and Pré-Bölling oscillations.     

A mathematical model of homologous recombination in cultured cells.

This work presents a model describing the rate of recombination between homologous segments of DNA stably integrated into the genome of cultured cells. The model has been applied to rat cell lines carrying the polyomavirus middle T oncogene and a functional origin of viral DNA replication. Introduction of the gene coding for the polyoma large T antigen or the SV40 large T antigen into cells by DNA transfection promotes homologous recombination in the resident viral inserts with rates varying between 0.1 x 10(-3) and 3.7 x 10(-1) per cell generation.     

A rapid method purifies a glycoprotein of Mr 145,000 as the LDL receptor of Trypanosoma brucei brucei

The trypanosome LDL receptor has been isolated from bloodstream form and cultured insect-stage trypanosomes as a protein of Mr 145,000, using a rapid purification procedure in the presence of a cocktail of protease inhibitors, whereas previously a polypeptide of Mr 86,000 was purified as the LDL receptor. Both the 145,000 and the 86,000 polypeptides are glycosylated and recognized by a monospecific antibody raised against the 86,000 species. This antibody inhibits LDL binding to the intact trypanosomes, to the isolated 145,000 receptor and to the 86,000 species. Hence, the previously isolated 86,000 polypeptide is a degradation product probably representing the cleaved-off ectodomain of the trypanosome LDL receptor.     

Polyoma virus mutant with normal transforming ability but impaired tumorigenic potential.

Cloned DNA from the P155 mutant of polyoma virus transforms cells in culture as efficiently as wild-type DNA, but has a much lower tumorigenic potential when injected into newborn rats. Like cells transformed by wild-type DNA, cells transformed by the mutant DNA grow in low serum concentrations, form colonies in agar suspension, and grow to high saturation densities compared with untransformed cells. They are, however, much less tumorigenic since they transplant 100- to 2,000-fold less efficiently than cells transformed by wild-type DNA. Substitution of the region between 89.7 and 1.8 map units by the corresponding region of P155 DNA decreased the tumorigenicity of wild-type DNA. When this region was isolated from wild-type DNA and substituted in P155 DNA, the tumorigenicity of the latter increased to values comparable to those of wild-type DNA. This showed that the lesion affecting tumorigenicity occurred between 89.7 and 1.8 map units on the polyoma virus genome. Sequence analysis in this region revealed a 12-base-pair deletion between nucleotides 1,347 and 1,360. This identified P155 as an mlt mutant, i.e., a mutant with a deletion from a region which encodes parts of the large and middle T antigens.     

Ultrastructural Changes of the Mitochondrion During the Life Cycle of Trypanosoma brucei

The mitochondrion is crucial for ATP generation by oxidative phosphorylation, among other processes. Cristae are invaginations of the mitochondrial inner membrane that house nearly all the macromolecular complexes that perform oxidative phosphorylation. The unicellular parasite Trypanosoma brucei undergoes during its life cycle extensive remodeling of its single mitochondrion, which reflects major changes in its energy metabolism. While the bloodstream form (BSF) generates ATP exclusively by substrate-level phosphorylation and has a morphologically highly reduced mitochondrion, the insect-dwelling procyclic form (PCF) performs oxidative phosphorylation and has an expanded and reticulated organelle. Here, we have performed high-resolution 3D reconstruction of BSF and PCF mitochondria, with a particular focus on their cristae. By measuring the volumes and surface areas of these structures in complete or nearly complete cells, we have found that mitochondrial cristae are more prominent in BSF than previously thought and their biogenesis seems to be maintained during the cell cycle. Furthermore, PCF cristae exhibit a surprising range of volumes in situ, implying that each crista is acting as an independent bioenergetic unit. Cristae appear to be particularly enriched in the region of the organelle between the nucleus and kinetoplast, the mitochondrial genome, suggesting this part has distinctive properties.     

Associations between Level and Change in Physical Function and Brain Volumes

Background

Higher levels of fitness or physical function are positively associated with cognitive outcomes but the potential underlying mechanisms via brain structure are still to be elucidated in detail. We examined associations between brain structure and physical function (contemporaneous and change over the previous three years) in community-dwelling older adults.

Methodology/Principal Findings

Participants from the Lothian Birth Cohort 1936 (N=694) underwent brain MRI at age 73 years to assess intracranial volume, and the volumes of total brain tissue, ventricles, grey matter, normal-appearing white matter, and white matter lesions. At ages 70 and 73, physical function was assessed by 6-meter walk, grip strength, and forced expiratory volume. A summary ‘physical function factor’ was derived from the individual measures using principal components analysis. Performance on each individual physical function measure declined across the three year interval (p<0.001). Higher level of physical function at ages 70 and 73 was associated with larger total brain tissue and white matter volumes, and smaller ventricular and white matter lesion volumes (standardized β ranged in magnitude from 0.07 to 0.17, p<0.001 to 0.034). Decline in physical function from age 70 to 73 was associated with smaller white matter volume (0.08, p<0.01, though not after correction for multiple testing), but not with any other brain volumetric measurements.

Conclusions/Significance

Physical function was related to brain volumes in community-dwelling older adults: declining physical function was associated with less white matter tissue. Further study is required to explore the detailed mechanisms through which physical function might influence brain structure, and vice versa.