Bacterial genes induced within the nodule during the Rhizobium–legume symbiosis

During the symbiosis between the bacterium Rhizobium meliloti and plants such as alfalfa, the bacteria elicit the formation of nodules on the roots of host plants. The bacteria infect the nodule, enter the cytoplasm of plant cells and differentiate into a distinct cell type called a bacteroid, which is capable of fixing atmospheric nitrogen. To discover bacterial genes involved in the infection and differentiation stages of symbiosis, we obtained genes expressed at the appropriate time and place in the nodule by identifying promoters that are able to direct expression of the bacA gene, which is required for bacteroid differentiation. We identified 230 fusions that are expressed predominantly in the nodule. Analysis of 23 sequences indicated that only three encode proteins known to be involved in the Rhizobium-legume symbiosis, six encode proteins with homology to proteins not previously associated with symbiosis, and 14 have no significant similarity to proteins of known function. Disruption of a locus that encodes a protein with homology to a cell adhesion molecule led to a defect in the formation of nitrogen-fixing nodules, resulting in an increased number of nitrogen-starved plants. Our isolation of a large number of nodule-expressed genes will help to open the intermediate stages of nodulation to molecular analysis.     

A role for synaptonemal complex in meiotic mismatch repair

A large subset of meiotic recombination intermediates form within the physical context of synaptonemal complex (SC), but the functional relationship between SC structure and homologous recombination remains obscure. Our prior analysis of strains deficient for SC central element proteins demonstrated that tripartite SC is dispensable for interhomolog recombination in Saccharomyces cerevisiae. Here, we report that while dispensable for recombination per se, SC proteins promote efficient mismatch repair at interhomolog recombination sites. Failure to repair mismatches within heteroduplex-containing meiotic recombination intermediates leads to genotypically sectored colonies (postmeiotic segregation events). We discovered increased postmeiotic segregation at THR1 in cells lacking Ecm11 or Gmc2, or in the SC-deficient but recombination-proficient zip1[Δ21-163] mutant. High-throughput sequencing of octad meiotic products furthermore revealed a genome-wide increase in recombination events with unrepaired mismatches in ecm11 mutants relative to wildtype. Meiotic cells missing Ecm11 display longer gene conversion tracts, but tract length alone does not account for the higher frequency of unrepaired mismatches. Interestingly, the per-nucleotide mismatch frequency is elevated in ecm11 when analyzing all gene conversion tracts, but is similar between wildtype and ecm11 if considering only those events with unrepaired mismatches. Thus, in both wildtype and ecm11 strains a subset of recombination events is susceptible to a similar degree of inefficient mismatch repair, but in ecm11 mutants a larger fraction of events fall into this inefficient repair category. Finally, we observe elevated postmeiotic segregation at THR1 in mutants with a dual deficiency in MutSγ crossover recombination and SC assembly, but not in the mlh3 mutant, which lacks MutSγ crossovers but has abundant SC. We propose that SC structure promotes efficient mismatch repair of joint molecule recombination intermediates, and that absence of SC is the molecular basis for elevated postmeiotic segregation in both MutSγ crossover-proficient (ecm11, gmc2) and MutSγ crossover-deficient (msh4, zip3) strains.     

Impact of anthropogenic sources on aerosol iron solubility over the Bay of Bengal and the Arabian Sea

Ambient aerosols collected from the marine atmospheric boundary layer of the Bay of Bengal and the Arabian Sea have been studied to assess the fractional solubility of aerosol iron, defined as Fe_ws (%)?=?Fe_ws/Fe_Tot?×?100; where Fe_Tot is total aerosol iron and Fe_ws is water soluble iron. The mass concentration of Fe_Tot over the two oceanic regions is not significantly different. However, the fractional solubility is 1–2 orders of magnitude higher over the Bay of Bengal (1.4–24%) compared to that over the Arabian Sea (0.02–0.4%). The spatio-temporal variability in Fe_ws (%) is attributed to differences in the nature of the mineral dust over the two oceanic regions. The Arabian Sea receives coarse dust from desert regions; whereas transport of alluvial dust from the Indo-Gangetic Plain is a dominant source to the Bay of Bengal. The poor fractional solubility (<1%) of Fe from mineral dust, hitherto overestimated in the literature, is documented for the Arabian Sea. A significant linear relationship (P-value?<?0.001) between Fe_ws (%), Fe_Tot and nss-SO₄ ^2? over the Bay of Bengal provides evidence for the chemical processing of mineral dust. Furthermore, the role of anthropogenic sources (biomass burning and fossil-fuel combustion) in enhancing the Fe_ws (%) is discernible from the chemical composition of fine mode (PM_2.5) aerosols over the Bay of Bengal. The potential impact of these Fe-dust depositions on phytoplankton carbon fixation and surface ocean biogeochemistry is discussed.     

Sexual dimorphism modifies habitat‐associated divergence: Evidence from beach and creek breeding sockeye salmon

Studies of parallel or convergent evolution (the repeated, independent evolution of similar traits in similar habitats) rarely explicitly quantify the extent of parallelism (i.e. variation in the direction and/or magnitude of divergence) between the sexes; instead, they often investigate both sexes together or exclude one sex. However, differences in male and female patterns of divergence could contribute to overall variation in the extent of parallelism among ecotype pairs, especially in sexually dimorphic traits. Failing to properly attribute such variation could lead to underestimates of the importance of environmental variation in shaping phenotypes. We investigate the extent of parallelism in the body shape of male and female beach and creek spawning sockeye salmon (Oncorhynchus nerka) from two lake systems in western Alaska that were colonized independently after the last ice age. Although both sexes showed some degree of parallelism, patterns of beach‐creek body shape divergence vary between the sexes and between lake systems. Phenotypic change vector analyses revealed highly parallel aspects of divergence between males from different lake systems (males from beaches had deeper bodies than males from creeks) but weaker parallelism in females and high parallelism between the sexes in one lake system but not the other. Body shape also had population‐specific components, which were mostly, but not entirely, explained by environmental variation in the form of creek depth. Our results highlight the importance of explicitly considering the extent of parallelism between the sexes and environmental variation among sites within habitat types.     

In Vivo Dynamics of Norepinephrine Release-Reuptake in Multiple Terminal Field Regions of Rat Brain

Abstract: Electrical stimulation of the ascending dorsal tegmental bundle of the locus ceruleus was used to elicit controlled release of norepinephrine. Real-time in vivo monitoring in the brains of urethane-anesthetized rats was observed with high speed chronocoulometry at rapidly responding carbon fiber electrodes. Using modeling similar to that developed for dopamine release, the electrochemical signals were characterized as the balance between norepinephrine release per electrical stimulation pulse and apparent Michaelis-Menten reuptake parameters. Stimulation produced simultaneous overflow release at all terminal fields examined. The release and reuptake characteristics varied considerably in different regions. If the parameters are normalized to endogenous concentration in the terminal fields, release but not reuptake correlates with innervation density in several regions. Stimulated release results in norepinephrine overflow and transport in most brain regions with half-lives of 1–3 s and overflow distances of 25–50 µm at most. A surprising exception occurs in the upper layers of cortex (cingulate and sensory) where half-lives may be in the 10s of seconds and spatial reach may be up to 100 µm. The uptake in the outer cortical layers appears to be minimal and comparable with only nonspecific reuptake.     

Synthesis of 4β-N-polyaromatic substituted podophyllotoxins: DNA topoisomerase inhibition, anticancer and apoptosis-inducing activities

A new class of 4β-N-polyaromatic substituted podophyllotoxin congeners have been synthesized and evaluated for their DNA topoisomerase-II (topo-II) inhibition as well as anticancer potential in some human cancer cell lines. The ease of synthesis and interesting biological activities make the present series of polyaromatic-podophyllotoxin congeners as a promising new structure for the development of new anticancer agents based on podophyllotoxin scaffold.     

Mechanical stretch activates signaling events for protein translation initiation and elongation in C2C12 myoblasts

It has been proposed that mechanically induced tension is the critical factor in the induction of muscle hypertrophy. However, the molecular mechanisms involved in this process are still under investigation. In the present study, the effect of mechanical stretch on intracellular signaling for protein translation initiation and elongation was studied in C2C12 myoblasts. Cells were grown on a silicone elastomer chamber and subjected to 30-min of 5 or 15% constant static or cyclic (60 cycles/min) uniaxial stretch. Western blot analyses revealed that p70 S6 kinase (p70S6K) and eukaryotic elongation factor 2 (eEF2), which are the markers for translation initiation and peptide chain elongation, respectively, were activated by both static and cyclic stretch. The magnitude of activation was greater in response to the 15% cyclic stretch. Cyclic stretch also increased the phosphorylation of MAP kinases (p38 MAPK, ERK1/2 and JNK). However, the pharmacological inhibition of MAP kinases did not block the stretch-induced activation of p70S6K and eEF2. An inhibitor of the mammalian target of rapamycin (mTOR) blocked the stretch-induced phosphorylation of p70S6K but did not affect the eEF2 activation. A broad-range tyrosine kinase inhibitor, genistein, blocked the stretch-induced activation of p70S6K and eEF2, whereas Src tyrosine kinase and Janus kinase (JAK) inhibitors did not. These results suggest that the stretch-induced activation of protein translation initiation and elongation in mouse myoblast cell lines is mediated by tyrosine kinase(s), except for Src kinase or JAK.     

Vesicular Calcium Regulates Coat Retention,Fusogenicity, and Size of Pre-Golgi Intermediates

The significance and extent of Ca²⁺ regulation of the biosynthetic secretory pathway have been difficult to establish, and our knowledge of regulatory relationships integrating Ca²⁺ with vesicle coats and function is rudimentary. Here, we investigated potential roles and mechanisms of luminal Ca²⁺ in the early secretory pathway. Specific depletion of luminal Ca²⁺ in living normal rat kidney cells using cyclopiazonic acid (CPA) resulted in the extreme expansion of vesicular tubular cluster (VTC) elements. Consistent with this, a suppressive role for vesicle-associated Ca²⁺ in COPII vesicle homotypic fusion was demonstrated in vitro using Ca²⁺ chelators. The EF-hand–containing protein apoptosis-linked gene 2 (ALG-2), previously implicated in the stabilization of sec31 at endoplasmic reticulum exit sites, inhibited COPII vesicle fusion in a Ca²⁺-requiring manner, suggesting that ALG-2 may be a sensor for the effects of vesicular Ca²⁺ on homotypic fusion. Immunoisolation established that Ca²⁺ chelation inhibits and ALG-2 specifically favors residual retention of the COPII outer shell protein sec31 on pre-Golgi fusion intermediates. We conclude that vesicle-associated Ca²⁺, acting through ALG-2, favors the retention of residual coat molecules that seem to suppress membrane fusion. We propose that in cells, these Ca²⁺-dependent mechanisms temporally regulate COPII vesicle interactions, VTC biogenesis, cargo sorting, and VTC maturation.     

Synthesis of MCC–PEG Conjugate and Its Evaluation as a Superdisintegrant

PEGylated conjugate of microcrystalline cellulose (MCC) was synthesized by reacting MCC with polyethylene glycol (PEG) 200 in the presence of catalyst at elevated temperature. Conjugation between MCC and PEG was confirmed by FT-IR and ¹H NMR studies. The conjugate showed 61% PEG content increase in molecular weight determined by mass spectroscopy. PEGylation did not improve solubility of cellulose significantly. The physico-chemical properties of conjugate were compared against MCC. This conjugate was evaluated for water vapor uptake isotherms, maximum water saturation, water penetration rate, disintegration time, superdisintegration power, and dissolution study. After comparing its results with that of commercial superdisintegrants, it can be concluded that MCC–PEG conjugate can prove to be a good superdisintegrant.