Voltage-induced gating of the mechanosensitive MscL ion channel reconstituted in a tethered lipid bilayer membrane

The mechanosensitive (MS) ion channel is gated by changes in bilayer deformation. It is functional without the presence of any other proteins and gating of the channel has been successfully achieved using conventional patch clamping techniques where a voltage has been applied together with a pressure over the membrane. Here, we have for the first time analyzed the large conducting (MscL) channel in a supported membrane using only an external electrical field. This was made possible using a newly developed technique utilizing a tethered lipid bilayer membrane (tBLM), which is part of an engineered microelectronic array chip. Single ion channel activity characteristic for MscL was obtained, albeit with lower conductivity. The ion channel was gated using solely a transmembrane potential of 300 mV. Computations demonstrate that this amount of membrane potential induces a membrane tension of 12 dyn/cm, equivalent to that calculated to gate the channel in patch clamp from pressure-induced stretching of the bilayer. These results strengthen the supposition that the MscL ion channel gates in response to stress in the lipid membrane rather than pressure across it. Furthermore, these findings illustrate the possibility of using the MscL as a release valve for engineered membrane devices; one step closer to mimicking the true function of the living cell.     

Issues in Bonobo (Pan paniscus) Sexual Behavior

Sexual behavior is one of the reported similarities between Pan paniscus and Homo sapiens that has stimulated recent interest in the phylogeny of the Pan and the Australopithecus/Homo genera. Similarities do exist, but an understanding of the forms and functions of Van paniscus sexual behavior is best achieved through a comparison to Pan troglodytes. Pan paniscus shows increased female receptivity, variability in copulatory position, male or female initiation of sexual behavior, differential male and female preferences for copulatory position, and association of food sharing and sexual behavior. Their sexual behavior appears to function in proximate terms as a tension-reduction mechanism. Lowered tension, in turn, facilitates multi-male, multi-female social groups. Lowered levels of aggression and increased sexual activity appear to be associated with paedomorphism, and the behavioral and anatomical/physiological characteristics of the species appear to be a consequence of a feeding ecology that promotes large groupings of the animals at preferential and comparatively rich feeding sites.     

Interaction between mobile DNA-element-induced lethal mutations and chemical mutagens in the hybrid dysgenic system of Drosophila melanogaster

Using the sex-linked recessive lethal mutation screen, a synergistic interaction is observed for mutations induced by chemical mutagens (ethyl methanesulfonate and dimethylnitrosamine) and the transposable DNA-element system of hybrid dysgenesis in spermatogonial cells of Drosophila melanogaster. Although the mechanism of this interaction is unknown, these results suggest that some chemical mutagens may induce transpositions, hybrid dysgenic cells may be more sensitive to chemically induced genetic damage, or hybrid dysgenesis may inhibit the efficiency of repair of chemically induced lesions.     

Study of the mitotic and meiotic chromosomes of sotol (<i>Dasylirion cedrosanum</i> Trel.)

The genus Dasylirion is a group of plants typically present in the Chihuahuan Desert, perennial, with a dioecious sexual behavior and commonly called sotoles. This genus has been little studied from the biological point of view, and the bases of its reproductive response remain unknown. In this work we studied the chromosome number and meiotic response of Dasylirion cedrosanum in the county of Saltillo, Coahuila, located at the North East of Mexico. For the preparation of mitotic chromosomes, we used a technique based on enzymatic treatment with pectolyase and cellulase, as well as staining with acetocarmin dye. For the study of meiosis, male flower buds were collected, fixed and stained for analysis with the same dye. As a result, the gametic (n = x = 19) and somatic chromosome (2n = 38) numbers of D. cedrosanum are reported for the first time, being consistent with previous findings in other Dasylirion species, which points to a constant ploidy level across the genus. Variation was observed in the morphology and size of the somatic chromosomes, with types ranging from submetacentric to subtelocentric, and sizes oscillating in a range of 4.43 µm, with an average total length of 112.38 µm for the diploid chromosome complement. This shows that the chromosome complement of D. cedrosanom would belong to a 3B classification of Stebins, with a medium variation between chromosome lengths and low chromosome asymmetry. This variation indicates the feasibility of constructing a chromosome ideotype for this species. The meiotic chromosome pairing showed a chromosome behavior consistent with a disomic inheritance characteristic of a diploid species, with prevalence of ring and chain bivalents, typically without pairing abnormalities. Bivalent configurations in all cases were symmetrical.The normal and symmetrical meiotic pairing indicates a balanced production of gametes, and suggests the absence of heteromorphic sex determination.     

Vaccination of castration-resistant prostate cancer patients with TroVax (MVA–5T4) in combination with docetaxel: a randomized phase II trial

The attenuated vaccinia virus, modified vaccinia Ankara, has been engineered to deliver the tumor antigen 5T4 (TroVax^®). Here, we report results from a randomized open-label phase II trial in castration-resistant prostate cancer patients in which TroVax was administered in combination with docetaxel and compared against docetaxel alone. The aim was to recruit 80 patients (40 per arm), but the study was terminated early due to recruitment challenges. Therefore, this paper reports the comparative safety and immunological and clinical efficacy in 25 patients, 12 of whom were treated with TroVax plus docetaxel and 13 with docetaxel alone. 5T4-specific immune responses were monitored throughout the study. Clinical responses were assessed by measuring changes in tumor burden by CT and bone scan and by quantifying PSA concentrations. TroVax was well tolerated in all patients. Of 10 immunologically evaluable patients, 6 mounted 5T4-specific antibody responses. Patients treated with TroVax plus docetaxel showed a greater median progression-free survival of 9.67 months compared with 5.10 months for patients on the docetaxel alone arm (P = 0.097; HR = 0.31; 95 % CI 0.08–1.24). Importantly, a pre-treatment biomarker previously demonstrated to predict 5T4 immune response and treatment benefit showed a strong association with 5T4 antibody response and a statistically significant association with progression-free survival in patients treated with TroVax plus docetaxel, but not docetaxel alone.     

Lactococcus lactis uses MscL as its principal mechanosensitive channel

The functions of the mechanosensitive channels from Lactococcus lactis were determined by biochemical, physiological, and electrophysiological methods. Patch-clamp studies showed that the genes yncB and mscL encode MscS and MscL-like channels, respectively, when expressed in Escherichia coli or if the gene products were purified and reconstituted in proteoliposomes. However, unless yncB was expressed in trans, wild type membranes of L. lactis displayed only MscL activity. Membranes prepared from an mscL disruption mutant did not show any mechanosensitive channel activity, irrespective of whether the cells had been grown on low or high osmolarity medium. In osmotic downshift assays, wild type cells survived and retained 20% of the glycine betaine internalized under external high salt conditions. On the other hand, the mscL disruption mutant retained 40% of internalized glycine betaine and was significantly compromised in its survival upon osmotic downshifts. The data strongly suggest that L. lactis uses MscL as the main mechanosensitive solute release system to protect the cells under conditions of osmotic downshift.     

Assessment of potential stimuli for mechano-dependent gating of MscL: effects of pressure, tension, and lipid headgroups

MscL is a mechanosensitive channel of large conductance that serves as an "emergency relief valve", protecting bacteria from acute hypoosmotic stress. Although it is well-accepted that the MscL protein and an adequate membrane matrix are necessary and sufficient for the function of this channel, the exact role of the membrane has yet to be elucidated. Here, we address the role of the membrane matrix through in vitro reconstitution of the MscL protein in defined lipid bilayers. We have applied Laplace's law to visualized membrane patches where we can measure patch curvature as described in previous studies. Here, by comparing patches with different curvatures, we demonstrate that the MscL channel senses tension within the membrane and that the pressure across it plays no detectable role as a stimulus. In addition, gating only occurs when the smallest radius of curvature is nearly achieved, suggesting that the lateral tension rather than membrane curvature is the important biophysical parameter. Finally, we have examined the contribution of specific headgroups by measuring their effect on the membrane tension required to gate the channel. We have found that the addition of neither anionic nor endogenous lipids to a non-native membrane effected a leftward shift in the activation curve. In fact, the major endogenous lipid of the Escherichia coli membrane, phosphatidylethanolamine, led to a channel activity at a higher tension threshold, suggesting that this lipid effects altered activity through changes in the biophysical properties of the membrane, rather than through an MscL-specific interaction.     

Carotenoids and life-history evolution in animals

Animals must allocate finite resources amongst competing demands. A suite of such trade-offs is thought to occur in the deployment of carotenoids, being widely responsible for sexual coloration and also important in antioxidant and immune defences. Experimental manipulation of dietary carotenoid availability is a useful approach for elucidating the mechanistic bases of carotenoid allocation trade-offs. Recent work using birds has shown that both sexual display and immune defences can be limited by carotenoid availability, providing support for the hypothesis that males allocating greater amounts of carotenoids to sexual coloration are advertising their superior health. Carotenoid availability has also been shown to limit egg-laying capacity in birds, although it remains to be seen whether carotenoid display in females advertises reproductive potential. More experiments are required to ascertain the importance of direct (material) and indirect (genetic) benefits accruing through choosing to mate with individuals that have greater carotenoid display.