Suppression of interleukin-2 and interleukin-2 receptor expression in Jurkat cells stably expressing the human immunodeficiency virus Tat protein.

The Jurkat T cell line was stably transfected with an Epstein-Barr virus-based episomal replicon designed to express high levels of the HIV-1 Tat protein. After selection in hygromycin B, high-level Tat activity was detected in 3 of 18 transfected cell lines. After stimulation with phytohemagglutinin (PHA) and phorbol myristate acetate (PMA), Tat transfectants with high Tat expression showed diminished expression of interleukin-2 (IL-2) and the interleukin-2 receptor alpha chain (IL-2R) when compared to untransfected Jurkat cells or Jurkat cell lines transfected with the parent control plasmid. Sublines derived from the high-level Tat transfectants with reduced Tat activity showed normalization of PHA/PMA-induced IL-2 expression. Northern analysis showed diminished expression of IL-2 and IL-2R mRNA in the stimulated Tat transfectants. Inhibition of IL-2 and IL-2R expression by the HIV-1 Tat protein may contribute to the immune suppression that characterizes HIV-1 infection.     

Human sperm characteristics during frequent ejaculation

Sperm concentration, morphology, DNA condensation and nuclear protein pattern as well as sperm adenylate cyclase were evaluated in semen samples provided by 7 volunteers every 8 h for 2 days. During the observation period, sperm concentration and total sperm number decreased but began to return towards normal after a 3-day abstinence period. No increase in the proportion of immature sperm cells was observed by light microscopy. Total adenylate cyclase (EC 4.6.1.1) increased significantly per cell, due to an increase in the soluble component while the particulate component remained relatively constant. Microflow fluorometry revealed no consistent alterations in the DNA or nuclear protein distribution. We conclude that although a high frequency of ejaculation does not disturb the conventional measures of sperm integrity, such as DNA condensation, there are major changes in at least one biochemical measurement, the activity of soluble adenylate cyclase.     

5 Alpha-reductase in the non-secretory cells of the rat ventral prostate epithelium

Kinetic constants for the 5 alpha-reductase were determined in freshly isolated epithelial cells from the rat ventral prostate. Studies were also performed on stromal tissue but not isolated stromal cells for comparison. Secretory and non-secretory epithelial cells were separated by centrifugation in a Percoll gradient. Both epithelial cell populations metabolized testosterone to predominantly 5 alpha-dihydrotestosterone (5 alpha-DHT), although when expressed per cell the capacity for conversion was 3-4-fold higher for secretory cells (7.4 pmol/min/10(6) cells) than for non-secretory cells (2.3 pmol/min/10(6) cells; P less than 0.01 in 4 separate studies). When compared per mg cytosol protein this difference became non-significant. Stromal tissue contained a 5 alpha-reductase Vmax (expressed) per mg protein) which was comparable to the non-secretory cell enzyme. Lineweaver-Burke plots revealed different Km values for the different cell populations (12.5, 5.9 and 4.7 microM for secretory, non-secretory and stromal cells, respectively) suggesting the presence of different isoforms of the enzyme, or differences in the intracellular concentrations of enzyme antagonists.     

Superoxide production by mitochondria isolated from green bell pepper fruit

Evidence is increasing to suggest that a wide range of environmentally induced plant disorders, including chilling injury, is mediated by reactive oxygen species produced during stress or upon relief from stress. Mitochondria were isolated from pericarp tissue of chilling-sensitive bell pepper fruit and their respiratory activity and ability to produce superoxide when supplied with NADH, succinate or malate-pyruvate were determined. Oxygen uptake rates were greater and less sensitive to cyanide with succinate than with NADH; rates increased and sensitivity to cyanide and respiratory control ratios (RCRs) decreased in fruit stored at 2°C. Disrupting mitochondrial membranes led to increased oxygen consumption with NADH and decreased consumption with succinate. resulting in RCRs of approximately 1 with both substrates. Superoxide production was greater with NADH than with either succinate or malatepyruvate. Superoxide dismutase and cyanide inhibited superoxide production almost completely. Antimycin A did not inhibit superoxide production with NADH, but did partially with succinate, especially in mitochondria sensitive to cyanide. Disrupting mitochondrial membranes enhanced superoxide production with NADH. Superoxide production by mitochondria isolated from fruit stored at 2°C increased with NADH and decreased with succinate. Results provide evidence that mitochondria may be a major source of superoxide in chilling-sensitive plant tissues exposed to low temperatures.     

Integrating ecology into macroevolutionary research

On 9 March, over 150 biologists gathered in London for the Centre for Ecology and Evolution spring symposium, 'Integrating Ecology into Macroevolutionary Research'. The event brought together researchers from London-based institutions alongside others from across the UK, Europe and North America for a day of talks. The meeting highlighted methodological advances and recent analyses of exemplar datasets focusing on the exploration of the role of ecological processes in shaping macroevolutionary patterns.     

A novel method for quantifying overdispersion in count data and its application to farmland birds

The statistical modelling of count data permeates the discipline of ecology. Such data often exhibit overdispersion compared with a standard Poisson distribution, so that the variance of the counts is greater than that of the mean. Whereas modelling to reveal the effects of explanatory variables on the mean is commonplace, overdispersion is generally regarded as a nuisance parameter to be accounted for and subsequently ignored. Instead, we propose a method that models the overdispersion as a biologically interesting property of a data set and show how novel inference is provided as a result. We adapted the double hierarchical generalized linear model approach to create an easily extendible model structure that quantifies the influence of explanatory variables on the overdispersion of count data, and apply it to farmland birds. These data were from a study within Irish agricultural ecosystems, in which total bird species abundance and the abundance of farmland indicator species were compared on dairy and non‐dairy farms in the winter and breeding seasons. In general, overdispersion in bird counts was greater on dairy farms than on non‐dairy farms, and for total bird numbers, overdispersion was greatest on dairy farms in winter. Our code is fitted using the Bayesian package Rstan, and we make all code and data available in a GitHub repository. Within a Bayesian framework, this approach facilitates a meaningful quantification of the effects of categorical explanatory variables on any response variable with a tendency to overdispersion that has a meaningful biological or ecological explanation.