13C magic angle spinning NMR evidence for a 15,15'-cis configuration of the spheroidene in the Rhodobacter sphaeroides photosynthetic reaction center.

The photosynthetic reaction center of Rhodobacter sphaeroides 2.4.1 contains one carotenoid that protects the protein complex against photodestruction. The structure around the central (15,15') double bond of the bound spheroidene carotenoid was investigated with low-temperature magic angle spinning 13C NMR, which allows an in situ characterization of the configuration of the central double bond in the carotenoid. Carotenoidless reaction centers of R. sphaeroides R26 were reconstituted with spheroidene specifically labeled at the C-14' or C-15' position, and the signals from the labels were separated from the natural abundance background using 13C MAS NMR difference spectroscopy. The resonances shift 5.2 and 3.8 ppm upfield upon incorporation in the protein complex, similar to the 5.6 and 4.4 ppm upfield shift occurring in the model compound beta-carotene upon trans to 15,15'-cis isomerization. Hence the MAS NMR favors a cis configuration, as opposed to the trans configuration deduced from X-ray data.     

Effect of plant nitrogen and water status on the foraging behavior and fitness of an omnivorous arthropod

Omnivorous arthropods make dietary choices according to the environment in which they forage, mainly availability/quality of plant and/or prey resources. Such decisions and their subsequent impacts on life‐history traits may be affected by the availability of nutrients and water to plants, that is, through bottom‐up forces. By setting up arenas for feeding behavior observation as well as glasshouse cages for plant preference assessment, we studied effects of the presence of prey (Lepidoptera eggs) and nitrogen/water availability to host tomato plants on the foraging behavior and life‐history traits in the omnivorous predator Macrolophus pygmaeus (Heteroptera: Miridae). In the absence of prey, the predator fed equally on the plants treated with various levels of nitrogen and water. In the presence of prey, however, the feeding rate on plants decreased when the plant received low water input. The feeding rate on prey was positively correlated with feeding rate on plants; that is, prey feeding increased with plant feeding when the plants received high water input. Moreover, plants receiving high water input attracted more M. pygmaeus adults compared with those receiving low water input. For M. pygmaeus fitness, the presence of prey enhanced its fertility and longevity, but the longevity decreased when plants received low compared with high water input. In conclusion, the omnivorous predator may be obliged to feed on plants to obtain water, and plant water status may be a limiting factor for the foraging behavior and fitness of the omnivorous predator.     

Surgical Injury to the Mouse Pancreas through Ligation of the Pancreatic Duct as a Model for Endocrine and Exocrine Reprogramming and Proliferation

Expansion of pancreatic beta cells in vivo or ex vivo, or generation of beta cells by differentiation from an embryonic or adult stem cell, can provide new expandable sources of beta cells to alleviate the donor scarcity in human islet transplantation as therapy for diabetes. Although recent advances have been made towards this aim, mechanisms that regulate beta cell expansion and differentiation from a stem/progenitor cell remain to be characterized. Here, we describe a protocol for an injury model in the adult mouse pancreas that can function as a tool to study mechanisms of tissue remodeling and beta cell proliferation and differentiation. Partial duct ligation (PDL) is an experimentally induced injury of the rodent pancreas involving surgical ligation of the main pancreatic duct resulting in an obstruction of drainage of exocrine products out of the tail region of the pancreas. The inflicted damage induces acinar atrophy, immune cell infiltration and severe tissue remodeling. We have previously reported the activation of Neurogenin (Ngn) 3 expressing endogenous progenitor-like cells and an increase in beta cell proliferation after PDL. Therefore, PDL provides a basis to study signals involved in beta cell dynamics and the properties of an endocrine progenitor in adult pancreas. Since, it still remains largely unclear, which factors and pathways contribute to beta cell neogenesis and proliferation in PDL, a standardized protocol for PDL will allow for comparison across laboratories.     

Evolutionary modification of mouth position in deuterostomes

In chordates, the oral ectoderm is positioned at the anterior neural boundary and is characterized by pituitary homeobox (Pitx) and overlapping Dlx and Six3 expressions. Recent studies have shown that the ectoderm molecular map is also conserved in hemichordates and echinoderms. However, the mouth develops in a more posterior position in these animals, in a domain characterized by Nkx2.1 and Goosecoid expression, in a manner similar to that observed in protostomes. Furthermore, BMP signaling antagonizes mouth development in echinoderms and hemichordates, but seems to promote oral ectoderm specification in chordates. Conversely, Nodal signaling appears to be required for oral ectoderm specification in sea urchins but not in chordates. The Nodal/BMP antagonism at work during ectoderm patterning thus seems to constitute a conserved feature in deuterostomes, and mouth relocation may have been accompanied by a change in the influence of BMP/Nodal signals on oral ectoderm specification. We suggest that the mouth primordium was located at the anterior neural boundary, in early chordate evolution. In extant chordate embryos, subsequent mouth positioning differ between urochordates and vertebrates, presumably as a consequence of surrounding tissues remodelling. We illustrate these morphogenetic movements by means of morphological data obtained by the confocal imaging of ascidian tailbud embryos, and provide a table for determining the tailbud stages of this model organism.     

DISENTANGLING PRECOPULATORY AND POSTCOPULATORY SEXUAL SELECTION IN POLYANDROUS SPECIES

Sexual selection operates on a sequence of events, from mating to offspring production. Which stages in this sequence undergo stronger selection, especially the relative importance of pre‐ versus postcopulatory processes, are intensely debated issues. Unequal siring success among mates of polyandrous females is classically taken as evidence for a large contribution of postcopulatory processes to the variance in male reproductive success (var(RS_m)). However, paternity skews also depend on the timing and number of copulations, a source of variation that should be considered precopulatory rather than postcopulatory. We develop a method for decomposing var(RS_m) accounting for copulatory activity and apply it to experimental mating groups of the snail Physa acuta. In our experiment, 40% of var(RS_m) emerges at the precopulatory stage, only half of which depends on variation in mating success (number of partners). Ignoring copulation characteristics can therefore lead to severe underestimation of precopulatory sexual selection. Moreover, although only 36% of var(RS_m) arises at the postcopulatory stage, this is when sexual selection on body weight mostly occurs. Finally, trade‐offs were detected between different components of precopulatory success, whereas pre‐ and postcopulatory success appear independent. Our study opens the way to a detailed quantitative understanding of sexual selection in polyandrous species.     

Prediction errors for state occupation and transition probabilities in multi‐state models

In this paper, we consider the estimation of prediction errors for state occupation probabilities and transition probabilities for multistate time‐to‐event data. We study prediction errors based on the Brier score and on the Kullback–Leibler score and prove their properness. In the presence of right‐censored data, two classes of estimators, based on inverse probability weighting and pseudo‐values, respectively, are proposed, and consistency properties of the proposed estimators are investigated. The second part of the paper is devoted to the estimation of dynamic prediction errors for state occupation probabilities for multistate models, conditional on being alive, and for transition probabilities. Cross‐validated versions are proposed. Our methods are illustrated on the CSL1 randomized clinical trial comparing prednisone versus placebo for liver cirrhosis patients.     

Transient optical spectroscopy of single crystals of the reaction center from Rhodobacter sphaeroides wild-type 2.4.1

The photoactivity of the crystallized reaction centers from Rhodobacter sphaeroides wild-type strain 2.4.1 has been examined by light-induced absorption spectral changes associated with charge separation and triplet state formation in the reaction center. Upon excitation of a crystal at ambient redox potential, the primary donor 865 nm band bleaches reversibly. The kinetics of its recovery were found to be biphasic with rate constants 11.5 +/- 1.3 s-1 and 0.9 +/- 0.4 s-1 which correspond to lifetimes of 87.0 +/- 9.0 ms and 1.0 +/- 0.7 s, respectively. The ratio of the fast-to-slow component preexponential terms was 3.5 +/- 1.1 suggesting that the majority (78.9 +/- 13.0%) of the reaction centers in the crystals lack the secondary quinone, QB. The addition of sodium ascorbate to the crystals attenuates the 865 nm absorption change, and gives rise to strong carotenoid triplet-triplet absorption changes at 547 nm. These data indicate that the reaction center-bound carotenoid in the crystals is capable of accepting triplet energy from the primary donor triplet.     

Linear dichroism of single crystals of the reaction center from Rhodobacter sphaeroides wild type strain 2.4.1

The linear dichroism of single crystals of the photochemical reaction center from Rhodobacter sphaeroides 2.4.1, expressed as the anisotropy (or polarization) ratio, p = (A – A )/A + A , relative to the long morphological axis of the crystals, has been measured to be –0.12±0.03 for the primary donor Q _y and -0.15±0.8 for the carotenoid. These dichroic effects can be predicted using data obtained from magnetophotoselection (Frank et al. 1979, McGann and Frank 1985) and electron spin resonance (ESR)(Frank et al. 1988a, Budil et al. 1988) experiments. Magnetophotoselection data yield the projections of the transition moments onto the primary donor triplet state principal magnetic axis system. The single crystal triplet state ESR experiments provide the Euler matrix for the transformation from the principal magnetic axis system to the crystal unit cell axis system. Thus, the projections of the transition moments (site 1) onto the crystal units cell axes (a, b, c) are determined to be-0.39, 0.90 and 0.18, respectively. The projections of the carotenoid transition moment (site 1) onto the crystal unit cell axes (a, b, c) are determined to be -0.60, 0.02 and 0.80, respectively. This information used in conjunction with the crystalline space group symmetry (P₂₁2₁2₁) and the morphology of the crystals allows one to predict the observed anisotropy ratios.