What Triggers Reproductive Life? Effects of Adolescent Cohabitation,Social Novelty and Aggression in a Monogamous Mouse

Cohabitation during childhood has been described as a powerful inhibitor of later sexual interest in animals including humans (the 'Westermarck effect'), serving as a brother–sister incest avoidance mechanism. Mound-building mice Mus spicilegus display a strong social inhibition of reproduction, responsible for the absence of reproduction in over-wintering tumuli. To better understand the mechanisms responsible for triggering reproduction in this monogamous species, we formed 100 experimental couples of juveniles (35 d) and surveyed reproduction for 45 d. As expected, very few couples reproduced, which confirms the role of social familiarity in the inhibition of reproduction. Temporary separation (1 h or 24 h) of the two partners had little effect on reproductive success. However, pairing with a new partner, with or without prior isolation, significantly triggered reproduction. Observations of the first encounter between new partners revealed more agonistic and less affiliative behaviour than in controls (reunion of familiar partners). Interestingly, when the new partner was a sibling of the previous one, the behavioural analysis revealed an intermediate level of aggression, indicating that kinship with the previous partner was perceived and had consequences on social behaviour. Mice could therefore choose a new partner based on its relatedness to the previous mate. Mutual tolerance between new partners during the dyadic encounter was negatively correlated with subsequent reproduction. These results demonstrate the paramount role of social novelty in triggering reproduction in this monogamous mouse, and suggest a link between agonistic behaviour and sexual motivation. In the field, mound-building mice may need to engage in agonistic interactions so as to overcome the long-lasting social inhibition of reproduction in overwintering mounds.     

Structural analysis of a glycoside hydrolase family 43 arabinoxylan arabinofuranohydrolase in complex with xylotetraose reveals a different binding mechanism compared with other members of the same family

AXHs (arabinoxylan arabinofuranohydrolases) are alpha-L-arabinofuranosidases that specifically hydrolyse the glycosidic bond between arabinofuranosyl substituents and xylopyranosyl backbone residues of arabinoxylan. Bacillus subtilis was recently shown to produce an AXH that cleaves arabinose units from O-2- or O-3-mono-substituted xylose residues: BsAXH-m2,3 (B. subtilis AXH-m2,3). Crystallographic analysis reveals a two-domain structure for this enzyme: a catalytic domain displaying a five-bladed beta-propeller fold characteristic of GH (glycoside hydrolase) family 43 and a CBM (carbohydrate-binding module) with a beta-sandwich fold belonging to CBM family 6. Binding of substrate to BsAXH-m2,3 is largely based on hydrophobic stacking interactions, which probably allow the positional flexibility needed to hydrolyse both arabinose substituents at the O-2 or O-3 position of the xylose unit. Superposition of the BsAXH-m2,3 structure with known structures of the GH family 43 exo-acting enzymes, beta-xylosidase and alpha-L-arabinanase, each in complex with their substrate, reveals a different orientation of the sugar backbone.     

Cadmium uptake and distribution in Arabidopsis thaliana exposed to low chronic concentrations depends on plant growth

This study tested the hypothesis that Cd uptake is correlated with the shoot or root growth of Arabidopsis thaliana ecotype Columbia cultivated hydroponically at environmentally relevant Cd concentrations: 20, 100 and 350 nmol L^?1. Growth of both roots and shoots were delayed at 350 nmol L^?1. The rate of Cd uptake determined by spiking the nutrient solution with ¹⁰⁹Cd for 24 h, was significantly correlated with the root growth rate. The fraction of Cd absorbed that was allocated to shoots was constant with time but decreased with increasing exposure to Cd. Autoradiography and gamma counting showed that Cd was preferentially allocated to developing leaves. Hence, the quantity of Cd in shoots depended both on the root growth, which probably governed the uptake, and on the maturity of the leaves, which may have determined the Cd allocated to shoots through changes in the transpiration stream.     

CFTR mediates cadmium-induced apoptosis through modulation of ROS level in mouse proximal tubule cells

The aim of this study was to characterize the role of CFTR during Cd²⁺-induced apoptosis. For this purpose primary cultures and cell lines originated from proximal tubules (PCT) of wild-type cftr^+/+ and cftr^?/? mice were used. In cftr^+/+ cells, the application of Cd²⁺ (5 μM) stimulated within 8 min an ERK1/2-activated CFTR-like Cl^? conductance sensitive to CFTR_inh-172. Thereafter Cd²⁺ induced an apoptotic volume decrease (AVD) within 6 h followed by caspase-3 activation and apoptosis. The early increase in CFTR conductance was followed by the activation of volume-sensitive outwardly rectifying (VSOR) Cl^? and TASK2 K⁺ conductances. By contrast, cftr^?/? cells exposed to Cd²⁺ were unable to develop VSOR currents, caspase-3 activity, and AVD process and underwent necrosis. Moreover in cftr^+/+ cells, Cd²⁺ enhanced reactive oxygen species (ROS) production and induced a 50% decrease in total glutathione content (major ROS scavenger in PCT). ROS generation and glutathione decrease depended on the presence of CFTR, since they did not occur in the presence of CFTR_inh-172 or in cftr^?/? cells. Additionally, Cd²⁺ exposure accelerates effluxes of fluorescent glutathione S-conjugate in cftr^+/+ cells. Our data suggest that CFTR could modulate ROS levels to ensure apoptosis during Cd²⁺ exposure by modulating the intracellular content of glutathione.     

On the importance of estimating detection probabilities from at‐sea surveys of flying seabirds

The primary and accepted method used to estimate seabird densities at sea from ships is the strip transect method, designed to correct for the effect of random directional bird movement relative to that of the ship. However, this method relies on the critical assumption that all of the birds within the survey strip are detected. We used the distance sampling method from line‐transects to estimate detection probability of a number of species of flying seabirds, and to test whether distance from the ship and bird body size affected detectability. Detection probability decreased from 0.987 (SE=0.029) to 0.269 (SE=0.035) with increasing strip half‐width from 100 to 1400 m. Detection probability also varied between size‐groups of species with strip half‐width. For all size‐groups, this probability was close to 1 for strip half‐width of 100 m, but was 0.869 (SE=0.115), 0.725 (SE=0.096) and 0.693 (SE=0.091) for strip half‐width of 300 m, a typical strip width used in seabird surveys, for respectively large, medium and small size flying seabirds. For larger strip half‐width, detection probability was higher for large sized species, intermediate for medium sized species and lower for smaller sized species. For strip half‐width larger than 100 m we suggest that more attention should be paid to testing the assumption of perfect detectability, because abundance estimates may be underestimated when this assumption is violated. Finally, the effect of the speed of travel of flying seabird on the detection probability was estimated in a simulation study, which suggests that detection probability was underestimated with increasing flying speed.     

Predicting future distributions of mountain plants under climate change: does dispersal capacity matter?

Many studies have investigated the potential impacts of climate change on the distribution of plant species, but few have attempted to constrain projections through plant dispersal limitations. Instead, most studies published so far have simplified dispersal as either unlimited or null. However, depending on the dispersal capacity of a species, landscape fragmentation, and the rate of climatic change, these assumptions can lead to serious over- or underestimation of the future distribution of plant species.
To quantify the discrepancies between simulations accounting for dispersal or not, we carried out projections of future distribution over the 21st century for 287 mountain plant species in a study area of the western Swiss Alps. For each species, simulations were run for four dispersal scenarios (unlimited dispersal, no dispersal, realistic dispersal, and realistic dispersal with long-distance dispersal events) and under four climate change scenarios.
Although simulations accounting for realistic dispersal limitations did significantly differ from those considering dispersal as unlimited or null in terms of projected future distribution, the unlimited dispersal simplification did nevertheless provide good approximations for species extinctions under more moderate climate change scenarios. Overall, simulations accounting for dispersal limitations produced, for our mountainous study area, results that were significantly closer to unlimited dispersal than to no dispersal. Finally, analysis of the temporal pattern of species extinctions over the entire 21st century revealed that important species extinctions for our study area might not occur before the 2080–2100 period, due to the possibility of a large number of species shifting their distribution to higher elevation.     

Accessing ns–μs side chain dynamics in ubiquitin with methyl RDCs

This study presents the first application of the model-free analysis (MFA) (Meiler in J Am Chem Soc 123:6098–6107, 2001; Lakomek in J Biomol NMR 34:101–115, 2006) to methyl group RDCs measured in 13 different alignment media in order to describe their supra-τ _c dynamics in ubiquitin. Our results indicate that methyl groups vary from rigid to very mobile with good correlation to residue type, distance to backbone and solvent exposure, and that considerable additional dynamics are effective at rates slower than the correlation time τ _c. In fact, the average amplitude of motion expressed in terms of order parameters S ² associated with the supra-τ _c window brings evidence to the existence of fluctuations contributing as much additional mobility as those already present in the faster ps-ns time scale measured from relaxation data. Comparison to previous results on ubiquitin demonstrates that the RDC-derived order parameters are dominated both by rotameric interconversions and faster libration-type motions around equilibrium positions. They match best with those derived from a combined J-coupling and residual dipolar coupling approach (Chou in J Am Chem Soc 125:8959–8966, 2003) taking backbone motion into account. In order to appreciate the dynamic scale of side chains over the entire protein, the methyl group order parameters are compared to existing dynamic ensembles of ubiquitin. Of those recently published, the broadest one, namely the EROS ensemble (Lange in Science 320:1471–1475, 2008), fits the collection of methyl group order parameters presented here best. Last, we used the MFA-derived averaged spherical harmonics to perform highly-parameterized rotameric searches of the side chains conformation and find expanded rotamer distributions with excellent fit to our data. These rotamer distributions suggest the presence of concerted motions along the side chains.     

Live-cell imaging of viral RNA genomes using a Pumilio-based reporter

We describe a method for localizing plant viral RNAs in vivo using Pumilio, an RNA-binding protein, coupled to bimolecular fluorescence complementation (BiFC). Two Pumilio homology domain (PUMHD) polypeptides, fused to either the N- or C-terminal halves of split mCitrine, were engineered to recognize two closely adjacent eight-nucleotide sequences in the genomic RNA of tobacco mosaic virus (TMV). Binding of the PUMHDs to their target sites brought the split mCitrine halves into close proximity, allowing BiFC to occur and revealing the localization of viral RNA within infected cells. The bulk of the RNA was sequestered in characteristic inclusion bodies known as viral replication complexes (VRCs), with a second population of RNA localized in discrete particles distributed throughout the peripheral cytoplasm. Transfer of the TMV Pumilio recognition sequences into the genome of potato virus X (PVX) allowed the PVX RNA to be localized. Unlike TMV, the PVX RNA was concentrated in distinctive 'whorls' within the VRC. Optical sectioning of the PVX VRCs revealed that one of the viral movement proteins was localized to the centres of the RNA whorls, demonstrating significant partitioning of viral RNA and proteins within the VRC. The utility of Pumilio as a fluorescence-based reporter for viral RNA is discussed.