Predictions of the somatic mutation and mortalization theories of cellular ageing are contrary to experimental observations

An accumulation of recessive lethal somatic mutations has often been proposed as a basis of cellular ageing. We have developed a mathematical model for the somatic mutation theory as applied to the finite in vitro lifespan of diploid fibroblast populations. Provided the mutation rate is sufficiently high, the model readily explains the cessation of proliferation of fibroblast cultures, but it predicts a much lower proportion of viable cells than is observed experimentally and also requires an unrealistically short cell division time. It is noted that the somatic mutation model is formally quite similar to the “mortalization” theory of Shall & Stein (1979), and that the mortalization theory is also incompatible with the same experimental data. We conclude that neither the somatic mutation theory nor the mortalization theory can explain the observed features of the growth of fibroblast populations in vitro. We discuss the possibility that deleterious mutations become important in the terminal stages of the lifespan, when they may accumulate as an indirect result of a general breakdown in information transfer between macromolecules.     

A re-examination of the effects of ionizing radiation on lifespan and transformation of human diploid fibroblasts.

Human diploid fibroblasts, strain MRC-5, were sequentially irradiated with 60Co gamma rays at intervals during their in vitro lifespan. The results indicate that 3 or 6 doses of 1 Gy can increase lifespan, and the same was true for cells treated with 3 doses of 3 Gy. Higher doses (5 x 3 Gy) did reduce growth potential, suggesting either that mid-late passage cells become more sensitive to radiation, or that doses beyond a given threshold reduce population lifespan by multiple cellular hits. The life extension induced by gamma rays might be due to an induced hypermethylation of DNA. Alternatively, oxygen radicals produced by irradiation might trigger an adaptive stress response which would remove damaged macromolecules and thereby increase the cells' growth potential. Whichever explanation is correct, the results show that the human fibroblast system is not appropriate for the study of the well known effect of ionizing radiation in shortening the lifespan of experimental animals. Contrary to earlier published results, populations of cells treated with cumulative doses of 15 Gy or 18 Gy and held for nearly 3 months after they had reached senescence (Phase III), produced no foci of transformed cells.     

Spatial patterns of Trybliographa rapae parasitism of Delia radicum larvae in oilseed rape and cauliflower

Trybliographa rapae (Westwood) is an important parasitoid of Delia radicum (L.). Parasitism of D. radicum larvae by T. rapae in relation to host density on canola (oilseed rape) and cauliflower roots was examined at 10 field sites in Germany and Switzerland. For roots with host larvae, the proportion of roots with one or more parasitized hosts increased with increasing host density. However, for these infested roots, the parasitism of individual larvae was not consistently related to host density. When considering only roots on which there were parasitized larvae and the opportunity for multiple attacks, the proportion of larvae that were parasitized decreased with increasing host density in the field locations, and in a cage study under controlled conditions. A model of patch‐finding and number of attacks by female parasitoids suggests that patch‐finding is density‐dependent, but that low attack rate and interference effects limit numbers of attacks to three or less per visit to a host patch; the reduced number of attacks per visit leads to the inverse relationship of larval parasitism with host density in the host patches visited. The interplay of the density‐dependent and inversely density‐dependent processes appears to be responsible for the inconsistency of density dependence of overall larval parasitism in this and previous studies. In the laboratory, adult female T. rapae parasitized hosts at ≤4 cm deep in soil, but not at 6 cm deep. From the depth distribution of larval feeding sites in the field, we infer that between 4% and 20% of Delia larvae may be in a physical refuge from T. rapae parasitism, which may have a stabilizing influence on the host–parasitoid interaction.     

Spectrum of heart diseases in a new cardiac service in Nigeria: An echocardiographic study of 1441 subjects in Abeokuta

Background

The recent determination of the complete nucleotide sequence of several Mycobacterium tuberculosis (MTB) genomes allows the use of comparative genomics as a tool for dissecting the nature and consequence of genetic variability within this species. The multiple alignment of the genomes of clinical strains (CDC1551, F11, Haarlem and C), along with the genomes of laboratory strains (H37Rv and H37Ra), provides new insights on the mechanisms of adaptation of this bacterium to the human host.

Findings

The genetic variation found in six M. tuberculosis strains does not involve significant genomic rearrangements. Most of the variation results from deletion and transposition events preferentially associated with insertion sequences and genes of the PE/PPE family but not with genes implicated in virulence. Using a Perl-based software islandsanalyser, which creates a representation of the genetic variation in the genome, we identified differences in the patterns of distribution and frequency of the polymorphisms across the genome. The identification of genes displaying strain-specific polymorphisms and the extrapolation of the number of strain-specific polymorphisms to an unlimited number of genomes indicates that the different strains contain a limited number of unique polymorphisms.

Conclusion

The comparison of multiple genomes demonstrates that the M. tuberculosis genome is currently undergoing an active process of gene decay, analogous to the adaptation process of obligate bacterial symbionts. This observation opens new perspectives into the evolution and the understanding of the pathogenesis of this bacterium.     

Rpp25 is a major target of autoantibodies to the Th/To complex as measured by a novel chemiluminescent assay

Introduction

Autoantibodies to the Th/To antigen have been described in systemic sclerosis (SSc) and several proteins of the macromolecular Th/To complex have been reported to react with anti-Th/To antibodies. However, anti-Th/To has not been clinically utilized due to unavailability of commercial tests. The objective of the present study is to evaluate the newly developed ELISA and chemiluminescent immunoassay (CLIA) to measure autoantibodies to Rpp25 (a component of the Th/To complex) using immunoprecipitation (IP) as the reference method.

Methods

The first cohort consisted of 123 SSc patients including 7 anti-Th/To positive samples confirmed by IP. Additional seven anti-Th/To positive samples from non-SSc patients were also tested. For evaluation of the QUANTA Flash Rpp25 CLIA (research use only), 8 anti-Th/To IP positives, a cohort of 70 unselected SSc patients and sera from various disease controls (n = 357) and random healthy individuals (n = 10) were studied.

Results

Anti-Rpp25 antibodies determined by ELISA were found in 11/14 anti-Th/To IP positive but only in 1/156 (0.6%) negative samples resulting in a positive percent agreement of 78.6% (95% confidence interval [CI] 49.2, 95.3%) and a negative percent agreement of 99.4% (95% CI 96.4, 100.0%). To verify the results using a second method, 53 samples were tested by ELISA and CLIA for anti-Rpp25 reactivity and the results were highly correlated (rho = 0.71, 95% CI 0.56, 0.81; P < 0.0001). To define the cutoff of the CLIA, anti-Th/To IP positive and negative sera were tested using the anti-Rpp25 CLIA. At the cutoff selected by receiver operating characteristic (ROC) analysis 8/8 (100.0%) of the anti-Th/To positive sera but only 2/367 (0.5%) of the controls were positive for anti-Rpp25 antibodies. The positive and negative percent agreements were 100.0% (95% CI 63.1, 100.0%) and 99.5% (95% CI 98.0, 99.9%), respectively. In the disease cohorts 2/70 (2.9%) of the SSc patients were positive for anti-Rpp25 antibodies compared to 2/367 (0.5%) of the controls (P = 0.032). ROC analysis showed discrimination between SSc patients and controls with an area under the curve value of 0.732 (95% CI 0.655, 0.809).

Conclusion

Rpp25 is a major target of autoantibodies to the Th/To autoantigen complex. Further studies are needed to evaluate the clinical utility of the new assays.