Dilute passage promotes expression of genetic and phenotypic variants of human immunodeficiency virus type 1 in cell culture.

We have studied the extent of genetic and phenotypic diversification of human immunodeficiency virus type 1 (HIV-1) upon 15 serial passages of clonal viral populations in MT-4 cell cultures. Several genetic and phenotypic modifications previously noted during evolution of HIV-1 in infected humans were also observed upon passages of the virus in cell culture. Notably, the transition from non-syncytium-inducing to syncytium-inducing phenotype (previously observed during disease progression) and fixation of amino acid substitutions at the main antigenic loop V3 of gp120 were observed in the course of replication of the virus in MT-4 cell cultures in the absence of immune selection. Interestingly, most genetic and phenotypic alterations occurred upon passage of the virus at a low multiplicity of infection (0.001 infectious particles per cell) rather than at a higher multiplicity of infection (0.1 infectious particles per cell). The degree of genetic diversification attained by HIV-1, estimated by the RNase A mismatch cleavage method and by nucleotide sequencing, is of about 0.03% of genomic sites mutated after 15 serial passages. This value is not significantly different from previous estimates for foot-and-mouth disease virus when subjected to a similar process and analysis. We conclude that several genetic and phenotypic modifications of HIV-1 previously observed in vivo occur also in the constant environment provided by a cell culture system. Dilute passage promotes in a highly significant way the expression of deviant HIV-1 genomes.     

Melatonin controls cell proliferation and modulates mitochondrial physiology in pancreatic stellate cells

Journal of Physiology and Biochemistry - We have investigated the effects of melatonin on major pathways related with cellular proliferation and energetic metabolism in pancreatic stellate cells....     

The evolution and ecology of multiple antipredator defences

Prey seldom rely on a single type of antipredator defence, often using multiple defences to avoid predation. In many cases, selection in different contexts may favour the evolution of multiple defences in a prey. However, a prey may use multiple defences to protect itself during a single predator encounter. Such “defence portfolios” that defend prey against a single instance of predation are distributed across and within successive stages of the predation sequence (encounter, detection, identification, approach (attack), subjugation and consumption). We contend that at present, our understanding of defence portfolio evolution is incomplete, and seen from the fragmentary perspective of specific sensory systems (e.g., visual) or specific types of defences (especially aposematism). In this review, we aim to build a comprehensive framework for conceptualizing the evolution of multiple prey defences, beginning with hypotheses for the evolution of multiple defences in general, and defence portfolios in particular. We then examine idealized models of resource trade-offs and functional interactions between traits, along with evidence supporting them. We find that defence portfolios are constrained by resource allocation to other aspects of life history, as well as functional incompatibilities between different defences. We also find that selection is likely to favour combinations of defences that have synergistic effects on predator behaviour and prey survival. Next, we examine specific aspects of prey ecology, genetics and development, and predator cognition that modify the predictions of current hypotheses or introduce competing hypotheses. We outline schema for gathering data on the distribution of prey defences across species and geography, determining how multiple defences are produced, and testing the proximate mechanisms by which multiple prey defences impact predator behaviour. Adopting these approaches will strengthen our understanding of multiple defensive strategies.     

Predator response to the coloured eyespots and defensive posture of Colombian four-eyed frogs

Deimatic displays, where sudden changes in prey appearance elicit aversive predator reactions, have been suggested to occur in many taxa. These (often only putative) displays frequently involve different components that may also serve antipredator functions via other mechanisms (e.g., mimicry, warning signalling, body inflation). The Colombian four-eyed frog, Pleurodema brachyops, has been suggested to gain protection against predation through putative deimatic displays where they inflate and elevate the posterior part of their body revealing eye-like colour markings. We exposed stationary artificial frogs to wild predators to test whether the two components (eyespot/colour markings, defensive posture) of their putative deimatic display, and their combination, provide protection from predation without the sudden change in appearance. We did not detect any obvious additive effect of defensive posture and eyespots/colour markings on predation risk, but found a marginally significant trend for model frogs in the resting posture to be less attacked when displaying eyespots/colour markings than when they were not, suggesting that the presence of colour markings/eyespots may provide some protection on its own. Additionally, we found that models in a resting posture were overall more frequently attacked on the head than models in a defensive posture, indicating that a defensive posture alone could help redirect predator attacks to non-vital parts of the body. The trends found in our study suggest that the different components of P. brachyops' coloration may serve different functions during a deimatic display, but further research is needed to elucidate the role of each component when accompanied by sudden prey movement.     

The Glucose-Related Decrease in Polar Auxin Transport During Ripening and its Possible Role in Grapevine Berry Coloring

Journal of Plant Growth Regulation - Auxin is a hormone that delays ripening in part by reducing anthocyanin content and impairing color development. Auxin content declines during the ripening...     

Identification of Dirofilaria immitis-infected dogs with a coagglutination assay.

The presence of Dirofilaria immitis excretory-secretory (ES) products was detected in the urine of infected dogs using a coagglutination assay. Urine samples from 30 naturally infected dogs were positive. Seventeen of them were microfilaremic, whereas 13 had become amicrofilaremic after receiving 2 courses of diethylcarbamazine. Urine samples from 20 dogs infected with other parasites, Dipetalonema reconditum (7), Toxocara canis (5), and Ancylostoma caninum (8), and urine samples from 20 healthy dogs were negative. The assay detected 200 ng/ml or more of ES products. This assay is simple, easy to perform with minimum training, and requires no equipment. Therefore it should be useful to detect canine filariasis under field conditions.     

Effect of internal and external K+ on Na+−Ca2+ exchange in dialyzed squid axons under voltage clamp conditions

The effect of external and internal K⁺ on Na_o⁺-dependent Ca²⁺ efflux was studied in dialyzed squid axons under constant membrane potential. With axons clamped at their resting potentials, external K⁺ (up to 70 mM) has no effect on Na⁺?Ca²⁺ exchange. Removal of K_i⁺ causes a marked inhibition in the Na_o⁺-dependent Ca²⁺ efflux component. Internal K⁺ activates the Na⁺?Ca²⁺ exchange with low affinity $\text{(K}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 90 mM)}$. Activation by K_i⁺ is similar in the presence or in the absence of Na_i⁺, thus ruling out a displacement of Na_i⁺ from its inhibitory site. Axons dialyzed with ATP also show a dependency of Ca²⁺ efflux on K_i⁺. The present results demonstrate that K_i⁺ is an important cofactor (partially required) for the proper functioning of the forward Na⁺?Ca²⁺ exchange.     

Potassium-induced insulin release and voltage noise measurements in single mouse islets of Langerhans

Summary Insulin release and membrane potential fluctuations in response to increased extracellular potassium [K⁺] _o have been measured in single perifused islets of Langerhans from normal mice. An increase in [K⁺] _o from 5mm to 50mm induced a transient insulin release with a peak at about 1 min. The peak value was [K⁺] _o -dependent but the half-timet _1/2 for the decline was constant at nearly 1 min. 2.5mm cobalt completely inhibited the potassium-induced stimulation of insulin release. The insulin release elicited by 28 and 50mm [K⁺] _o was similar in terms of peak, total release and half-time from maximum release. Stepwise increase in [K⁺] _o from 10 to 28 to 50mm resulted in a normal response to 28mm but no peak of release after the 28 to 50mm increase. The results indicate good correlation between excess voltage noise, thought to reflect calcium channel activity, and insulin release evoked by changing extracellular potassium.     

Effects of progesterone and estradiol on the proliferation of phytohemagglutinin-stimulated human lymphocytes

In this paper we report on a study to elucidate whether the response of human lymphocytes to mitogenic stimulation was modified by physiological changes which occur during the menstrual cycle. Experiments with untreated cultures showed intra-individual variation to mitogen stimulation in female lymphocyte cultures, but a significant correlation between the menstrual cycle and the proliferation kinetics of lymphocytes was not found. Consequently, we performed experiments in which two of the hormones that regulate the menstrual cycle in women, estradiol and progesterone, were added to cultured human lymphocytes obtained from both men and women. The results indicate that both hormones at physiological concentrations have the capacity to modify the proliferation of PHA-stimulated human lymphocytes. Therefore, both hormones could play a role in the induction of the intra-individual variation observed in the untreated female cultures. However, in vivo other factors could also modify the proliferation kinetics of human lymphocytes preventing the demonstration of the effects of a single factor, such as the hormonal changes occurring during the menstrual cycle.     

Sensitivity to in vitro lipid peroxidation in liver and brain of aged rats.

Lipid peroxidation in rat liver and brain has been studied to see if it increases with old age. No significant differences in the level of endogenous, nonstimulated lipid peroxidation (TBA-RS) is found between 9 month-old (mature adults) and 28 month-old animals in liver or cerebral cortex. Liver homogenates subjected in vitro to an oxidative stress (ascorbate-Fe++), show a clearly slower peroxidation rate in old than in young animals. On the other hand, the in vitro peroxidation rate of cerebral homogenates was similar in young and old animals. The in vitro peroxidation rate was much higher in brain than in liver tissue. These results do not support the view that old rats liver and brain are more susceptible to free radical oxidative damage than those of young ones.