Neisseria gonorrhoeae Modulates Iron-Limiting Innate Immune Defenses in Macrophages

Neisseria gonorrhoeae is a strict human pathogen that causes the sexually transmitted infection termed gonorrhea. The gonococcus can survive extracellularly and intracellularly, but in both environments the bacteria must acquire iron from host proteins for survival. However, upon infection the host uses a defensive response by limiting the bioavailability of iron by a number of mechanisms including the enhanced expression of hepcidin, the master iron-regulating hormone, which reduces iron uptake from the gut and retains iron in macrophages. The host also secretes the antibacterial protein NGAL, which sequesters bacterial siderophores and therefore inhibits bacterial growth. To learn whether intracellular gonococci can subvert this defensive response, we examined expression of host genes that encode proteins involved in modulating levels of intracellular iron. We found that N. gonorrhoeae can survive in association (tightly adherent and intracellular) with monocytes and macrophages and upregulates a panel of its iron-responsive genes in this environment. We also found that gonococcal infection of human monocytes or murine macrophages resulted in the upregulation of hepcidin, NGAL, and NRAMP1 as well as downregulation of the expression of the gene encoding the short chain 3-hydroxybutyrate dehydrogenase (BDH2); BDH2 catalyzes the production of the mammalian siderophore 2,5-DHBA involved in chelating and detoxifying iron. Based on these findings, we propose that N. gonorrhoeae can subvert the iron-limiting innate immune defenses to facilitate iron acquisition and intracellular survival.     

Comparing Springtime Ice-Algal Chlorophyll a and Physical Properties of Multi-Year and First-Year Sea Ice from the Lincoln Sea

With near-complete replacement of Arctic multi-year ice (MYI) by first-year ice (FYI) predicted to occur within this century, it remains uncertain how the loss of MYI will impact the abundance and distribution of sea ice associated algae. In this study we compare the chlorophyll a (chl a) concentrations and physical properties of MYI and FYI from the Lincoln Sea during 3 spring seasons (2010-2012). Cores were analysed for texture, salinity, and chl a. We identified annual growth layers for 7 of 11 MYI cores and found no significant differences in chl a concentration between the bottom first-year-ice portions of MYI, upper old-ice portions of MYI, and FYI cores. Overall, the maximum chl a concentrations were observed at the bottom of young FYI. However, there were no significant differences in chl a concentrations between MYI and FYI. This suggests little or no change in algal biomass with a shift from MYI to FYI and that the spatial extent and regional variability of refrozen leads and younger FYI will likely be key factors governing future changes in Arctic sea ice algal biomass. Bottom-integrated chl a concentrations showed negative logistic relationships with snow depth and bulk (snow plus ice) integrated extinction coefficients; indicating a strong influence of snow cover in controlling bottom ice algal biomass. The maximum bottom MYI chl a concentration was observed in a hummock, representing the thickest ice with lowest snow depth of this study. Hence, in this and other studies MYI chl a biomass may be under-estimated due to an under-representation of thick MYI (e.g., hummocks), which typically have a relatively thin snowpack allowing for increased light transmission. Therefore, we suggest the on-going loss of MYI in the Arctic Ocean may have a larger impact on ice–associated production than generally assumed.     

Xanthate sulfur as a hydrogen bond acceptor: the free xanthate anion and ligand sulfur in nickel tris ethylxanthate

Xanthates, like thiolates, form a variety of complexes with metals in which coordinating sulfur can serve as a hydrogen bond acceptor. Nickel tris xanthate complexes [Ni(xan)₃]⁻, (xan = o-ethylxanthate, N-(carbamoylmethyl)ethylxanthate) have been synthesized and compared by a combination of X-ray crystallographic and spectroscopic measurements. Recent results from our studies of N-H?S hydrogen bonding interactions in metal-xanthate complexes shows N-S distances to be longer than those in related thiolate complexes, indicative of weaker hydrogen bonds for the xanthates. The complex (Et₄N)[N-(carbamoylmethyl)ethylxanthate)] adopts an extended conformation in both the solid state and solution and lacks either intraligand or intermolecular N-H?S hydrogen bonds. The complex (CTA)[Ni(exa)₃] exhibits N-H?S hydrogen bonds between the amide group of the counterion and the ligand sulfur. The amide-sulfur N-H?S distance is 3.567 Å.     

Targeted Deletion of FGL2 Leads to Increased Early Viral Replication and Enhanced Adaptive Immunity in a Murine Model of Acute Viral Hepatitis Caused by LCMV WE

Mounting effective innate and adaptive immune responses are critical for viral clearance and the generation of long lasting immunity. It is known that production of inhibitory factors may result in the inability of the host to clear viruses, resulting in chronic viral persistence. Fibrinogen-like protein 2 (FGL2) has been identified as a novel effector molecule of CD4⁺CD25⁺ Foxp3⁺ regulatory T (Treg) cells that inhibits immune activity by binding to FCγRIIB expressed primarily on antigen presenting cells (APC). In this study, we show that infection of mice with Lymphocytic Choriomeningitis Virus WE (LCMV WE) leads to increased plasma levels of FGL2, which were detected as early as 2 days post-infection (pi) and persisted until day 50 pi. Mice deficient in FGL2 (fgl2^−/−) had increased viral titers of LCMV WE in the liver early p.i but cleared the virus by day 12 similar to wild type mice. Dendritic cells (DC) isolated from the spleens of LCMV WE infected fgl2^−/− had increased expression of the DC maturation markers CD80 and MHC Class II compared to wild type (fgl2^+/+). Frequencies of CD8⁺ and CD4⁺ T cells producing IFNγ in response to ex vivo peptide re-stimulation isolated from the spleen and lymph nodes were also increased in LCMV WE infected fgl2 ^−/− mice. Increased frequencies of CD8⁺ T cells specific for LCMV tetramers GP₃₃ and NP₃₉₆ were detected within the liver of fgl2^−/− mice. Plasma from fgl2^−/− mice contained higher titers of total and neutralizing anti-LCMV antibody. Enhanced anti-viral immunity in fgl2^−/− mice was associated with increased levels of serum alanine transaminase (ALT), hepatic necrosis and inflammation following LCMV WE infection. These data demonstrate that targeting FGL2 leads to early increased viral replication but enhanced anti-viral adaptive T & B cell responses. Targeting FGL2 may enhance the efficacy of current anti-viral therapies for hepatotropic viruses.     

The dynamics of climate-induced range shifting; perspectives from simulation modelling

Predicted future climate change will alter species' distributions as they attempt to track the most suitable 'climate window'. Climate envelope models indicate the direction of likely range changes but do not incorporate population dynamics, therefore observed responses may differ greatly from these projections. We use simulation modelling to explore the consequences of a period of environmental change for a species structured across an environmental gradient. Results indicate that a species' range may lag behind its climate envelope and demonstrate that the rate of movement of a range can accelerate during a period of climate change. We conclude that the inclusion of both population dynamics and spatial environmental variability is vital to develop models that can both predict, and be used to manage, the impact of changing climate on species' biogeography.     

Preimplantation Mouse Embryo Selection Guided by Light-Induced Dielectrophoresis

Selection of optimal quality embryos for in vitro fertilization (IVF) transfer is critical to successful live birth outcomes. Currently, embryos are chosen based on subjective assessment of morphologic developmental maturity. A non-invasive means to quantitatively measure an embryo''s developmental maturity would reduce the variability introduced by the current standard. We present a method that exploits the scaling electrical properties of pre-transfer embryos to quantitatively discern embryo developmental maturity using light-induced dielectrophoresis (DEP). We show that an embryo''s DEP response is highly correlated with its developmental stage. Uniquely, this technique allows one to select, in sequence and under blinded conditions, the most developmentally mature embryos among a mixed cohort of morphologically indistinguishable embryos cultured in optimized and sub-optimal culture media. Following assay, embryos continue to develop normally in vitro. Light-induced dielectrophoresis provides a non-invasive, quantitative, and reproducible means to select embryos for applications including IVF transfer and embryonic stem cell harvest.     

Maize C4 photosynthesis involves differential regulation of phosphoenolpyruvate carboxylase genes

Maize as a C4 plant partitions CO2 fixation in two consecutive, spatially separated steps, thus eliminating photorespiration. The crucial enzyme for primary CO2 fixation is a C4-specific phosphoenolpyruvate carboxylase (PEPC). The differential expression of the unique C4-specific gene pepcZm1 and two non-C4-specific genes, pepcZm2A and pepcZm3B, in leaf, root, and stem is reported here. It is shown, in a transient homologous system, that this tissue-specific regulation is mainly controlled by their distinct promoters. The light induction of the C4-specific pepcZm1 in illuminated etiolated (greening) leaves probably relies on light-dependent developmental changes instead of an immediate responsiveness found for other maize genes. Analyses of deleted, mutated, and hybrid promoters revealed the redundant nature of a 14mer which is repeated four times and a decisive function of the TATA box-like motif, TATTT, and the sequences directly preceding it. No consensus sequences to other photosynthetic gene promoters were uncovered. Although light induces the expression of C4 PEPC and other photosynthetic genes in maize, this co-ordination is apparently mediated through different signal transduction pathways and distinct regulatory elements. This study indicates that the acquisition of a new promoter is at least partially responsible for the C4-specific expression of pepcZm1 essential for C4 photosynthesis.