The origins of the back-mutation assay method: a personal recollection

The back-mutation assay method for determining the mutagenicity of various treatments was first developed a little over 50 years ago and has been in continuous use ever since. Shortly after the method was first used it became evident that certain factors of cell density, composition of media, etc., had to be carefully controlled to preserve an acceptable reliability of the method. A factor of particular importance was the suppression of growth of back-mutant prototrophic cells by the large number of auxotrophic cells present, a phenomenon which later became known as the "Grigg Effect." This review describes the origins of the back-mutation method and of the confounding competitive suppression phenomenon, the cause of competitive suppression, methods of diagnosing whether it is likely to bias the interpretation of a particular back-mutation experiment, and an experimental design which removes it entirely as a possible source of error. A number of other phenomena, such as phenotypic lag and coincident mutation associated with back-mutation, are also discussed as possible sources of error.     

Comparison of responses to tensile and compressive stimuli in C-mechanosensitive nociceptors in rat hairy skin

Mechanosensitive nociceptors with unmyelinated axons (C-fibers) were studied in a preparation of isolated skin and nerve from rat. Afferent discharges were recorded while the skin was mechanically stimulated using quantitative stretch (tension) and indentation (compression). The apparatus allowed for generating stimuli of equal magnitudes in both tension and compression. Stimulus-response functions were obtained for individual afferents relating discharge rate to tensile stress or compressive stress. A response threshold and maximal slope were obtained from each function. Thresholds did not differ significantly for compression and tension nor did the maximal slopes. We conclude that C-nociceptors are equally sensitive to tensile and compressive stress.     

Lack of a Functioning P2X7 Receptor Leads to Increased Susceptibility to Toxoplasmic Ileitis

Background

Oral infection of C57BL/6J mice with the protozoan parasite Toxoplasma gondii leads to a lethal inflammatory ileitis.

Principal Findings

Mice lacking the purinergic receptor P2X7R are acutely susceptible to toxoplasmic ileitis, losing significantly more weight than C57BL/6J mice and exhibiting much greater intestinal inflammatory pathology in response to infection with only 10 cysts of T. gondii. This susceptibility is not dependent on the ability of P2X7R-deficient mice to control the parasite, which they accomplish just as efficiently as C57BL/6J mice. Rather, susceptibility is associated with elevated ileal concentrations of pro-inflammatory cytokines, reactive nitrogen intermediates and altered regulation of elements of NFκB activation in P2X7R-deficient mice.

Conclusions

Our data support the thesis that P2X7R, a well-documented activator of pro-inflammatory cytokine production, also plays an important role in the regulation of intestinal inflammation.     

The longevity of constructed log pile fauna habitats in restored bauxite mines in relation to recurrent wildfire in the jarrah forest of Western Australia

Coarse woody debris (CWD) is often returned to rehabilitated areas after mining to provide specific habitat features for fauna that might otherwise take many decades to develop naturally. The CWD, typically constructed into log piles, is assumed to persist for comparable periods of time to fulfil their role. In the fire‐prone jarrah forest in Western Australia, these structures will be subject to recurrent wildfire, but there is little information on their survival. In January 2006, a wildfire burnt through 310 ha of rehabilitation at Alcoa’s Willowdale bauxite mine, 140 km south east of Perth, enabling the first estimates of the longevity of log pile fauna habitats to be made. Reductions in numbers of logs were greatest for small (<30 cm diameter) logs (48%), intermediate for large (>30 cm diameter) logs (37%) and least for stumps (17%). Assuming an exponential decay pattern, half‐lives of 1.1, 1.5 and 3.7 wildfires were calculated for small logs, large logs and stumps respectively, from which we estimate a useful ‘life’ of a typical log pile fauna habitat of 57–73 years. Increasing fire intensity was associated with greater reductions in the number of large logs, significantly greater surface charring and, at the highest intensity, significantly fewer crevices compared to unburnt log piles. Implications of these findings for the management of log piles in rehabilitation and CWD in the adjacent unmined forest, and of the role of prescribed fire, are discussed.     

Comparative genomic analysis reveals significant enrichment of mobile genetic elements and genes encoding surface structure-proteins in hospital-associated clonal complex 2 Enterococcus faecalis

Background  

Enterococci rank among the leading causes of nosocomial infections. The failure to identify pathogen-specific genes in Enterococcus faecalis has led to a hypothesis where the virulence of different strains may be linked to strain-specific genes, and where the combined endeavor of the different gene-sets result in the ability to cause infection. Population structure studies by multilocus sequence typing have defined distinct clonal complexes (CC) of E. faecalis enriched in hospitalized patients (CC2, CC9, CC28 and CC40).     

Regenerative potential of human muscle stem cells in chronic inflammation

Introduction

Chronic inflammation is a profound systemic modification of the cellular microenvironment which could affect survival, repair and maintenance of muscle stem cells. The aim of this study was to define the role of chronic inflammation on the regenerative potential of satellite cells in human muscle.

Methods

As a model for chronic inflammation, 11 patients suffering from rheumatoid arthritis (RA) were included together with 16 patients with osteoarthritis (OA) as controls. The mean age of both groups was 64 years, with more females in the RA group compared to the OA group. During elective knee replacement surgery, a muscle biopsy was taken from the distal musculus vastus medialis. Cell populations from four RA and eight OA patients were used for extensive phenotyping because these cell populations showed no spontaneous differentiation and myogenic purity greater than 75% after explantation.

Results

After mononuclear cell explantation, myogenic purity, viability, proliferation index, number of colonies, myogenic colonies, growth speed, maximum number of population doublings and fusion index were not different between RA and OA patients. Furthermore, the expression of proteins involved in replicative and stress-induced premature senescence and apoptosis, including p16, p21, p53, hTERT and cleaved caspase-3, was not different between RA and OA patients. Mean telomere length was shorter in the RA group compared to the OA group.

Conclusions

In the present study we found evidence that chronic inflammation in RA does not affect the in vitro regenerative potential of human satellite cells. Identification of mechanisms influencing muscle regeneration by modulation of its microenvironment may, therefore, be more appropriate.