Cross-Basin Comparison of Phosphorus Stress and Nitrogen Fixation in Trichodesmium

We investigated the phosphorus (P) status and N2 fixation rates of Trichodesmium populations from the North Pacific, western South Pacific, and western North Atlantic. Colonies of Trichodesmium were collected and analyzed for endogenous alkaline phosphatase (AP) activity using enzyme-labeled fluorescence ( ELF) and for nitrogenase activity using acetylene reduction. AP hydrolyzes dissolved inorganic phosphate (DIP) from dissolved organic phosphorus and is active in Trichodesmium colonies experiencing P stress. Across multiple stations in the subtropical North and South Pacific, there was low to moderate ELF labeling in Trichodesmium, although labeling was present in other taxa. In contrast, Trichodesmium ELF labeling in the North Atlantic ranged from low to high. Low ELF labeling corresponded with high DIP concentrations while high ELF labeling occurred only at North Atlantic stations with DIP concentrations \u3c = 40 nmol L-1, indicating that Trichodesmium was not experiencing dramatic P stress in the Pacific Ocean while P stress was evident in the western North Atlantic. However, nitrogenase activity was significantly higher in the P-stressed western North Atlantic than in the Pacific Ocean (0.40-1.30 compared to 0.01-0.46 nmol C2H4 h-1 colony-1. These data underscore the differential basin-level importance of P availability to Trichodesmium and suggest that factors other than P are constraining their N2 fixation rates in the Pacific

Influences of Excluded Volume of Molecules on Signaling Processes on Biomembrane

We investigate the influences of the excluded volume of molecules on biochemical reaction processes on 2-dimensional surfaces using a model of signal transduction processes on biomembranes. We perform simulations of the 2-dimensional cell-based model, which describes the reactions and diffusion of the receptors, signaling proteins, target proteins, and crowders on the cell membrane. The signaling proteins are activated by receptors, and these activated signaling proteins activate target proteins that bind autonomously from the cytoplasm to the membrane, and unbind from the membrane if activated. If the target proteins bind frequently, the volume fraction of molecules on the membrane becomes so large that the excluded volume of the molecules for the reaction and diffusion dynamics cannot be negligible. We find that such excluded volume effects of the molecules induce non-trivial variations of the signal flow, defined as the activation frequency of target proteins, as follows. With an increase in the binding rate of target proteins, the signal flow varies by i) monotonically increasing; ii) increasing then decreasing in a bell-shaped curve; or iii) increasing, decreasing, then increasing in an S-shaped curve. We further demonstrate that the excluded volume of molecules influences the hierarchical molecular distributions throughout the reaction processes. In particular, when the system exhibits a large signal flow, the signaling proteins tend to surround the receptors to form receptor-signaling protein clusters, and the target proteins tend to become distributed around such clusters. To explain these phenomena, we analyze the stochastic model of the local motions of molecules around the receptor.Comment: 31 pages, 10 figure

Réponse insuffisante à la stimulation en vue de FIV : maintenir la ponction ou choisir l' insémination ?

In women undergoing controlled ovarian hyperstimulation (COH) for in vitro fertilization (IVF), a poor ovarian response, defined as three of fewer mature follicles, can lead to cancellation of the cycle. However, in women with at least one patent tube and normal semen parameters, conversion to intrauterine insemination (IUI) is considered an option, offering reasonable pregnancy rates at a lower cost and without the complications associated with oocyte retrieval. Studies have shown that in cycles with only one mature follicle, IVF should be canceled. However, in cycles with 2 or 3 mature follicles, patients have the choice between IVF and conversion to IUI. Some studies have shown that IVF is superior to IUI in such cases, whereas other reports failed to find any difference. Most of these studies are retrospective and limited by the presence of several biases and low numbers of cycles, and to this date, there is no consensus on the best approach. We have thus designed a multicenter, randomized non-inferiority study, comparing live birth rates following conversion to IUI or IVF in patients with 2 or 3 mature follicles in COH cycles. Nine hundred and forty patients will be randomized on trigger day to either IVF or conversion to IUI. Our study will also include a medico-economic analysis

Surgical treatment of septate uterus in cases of primary infertility and before assisted reproductive technologies

Septate uterus is the most common congenital uterine malformation in women with infertility. Several criteria are available for the definition of septate uteri, such as the one proposed by the European Society of Human Reproduction and Embryology (ESHRE)/European Society for Gynecological Endoscopy (ESGE) (ESHRE/ESGE), or by the American Society for Reproductive Medicine (ASRM), with notable differences between the two. Recently, a simplified classification was proposed by the Congenital Uterine Malformations Experts (CUME), where a septum is defined as an internal indentation depth≥10mm. To date, there is no consensus on the management of women with a septate uterus and infertility. We have performed an extensive literature appraisal and reviewed all the available international guidelines in order to propose a management strategy for infertile patients with a uterine septum. Hysteroscopic septum incision seems to improve natural conception rates in the year following surgery. Moreover, it improves in vitro fertilization (IVF) outcomes when performed before the embryo transfer, by improving embryo implantation rates. On the other hand, for patients with an arcuate uterus (indentation<1.5cm according to the ASRM guidelines) and infertility, it seems that assisted reproductive technologies are the most appropriate first line treatment. However, in cases of recurrent implantation failure or recurrent pregnancy loss following IVF, hysteroscopic section could be proposed. Overall, we recommend hysteroscopic septum incision for patients with primary infertility, and for patients undergoing assisted reproductive technologies

Receptor Complementation and Mutagenesis Reveal SR-BI as an Essential HCV Entry Factor and Functionally Imply Its Intra- and Extra-Cellular Domains

HCV entry into cells is a multi-step and slow process. It is believed that the initial capture of HCV particles by glycosaminoglycans and/or lipoprotein receptors is followed by coordinated interactions with the scavenger receptor class B type I (SR-BI), a major receptor of high-density lipoprotein (HDL), the CD81 tetraspanin, and the tight junction protein Claudin-1, ultimately leading to uptake and cellular penetration of HCV via low-pH endosomes. Several reports have indicated that HDL promotes HCV entry through interaction with SR-BI. This pathway remains largely elusive, although it was shown that HDL neither associates with HCV particles nor modulates HCV binding to SR-BI. In contrast to CD81 and Claudin-1, the importance of SR-BI has only been addressed indirectly because of lack of cells in which functional complementation assays with mutant receptors could be performed. Here we identified for the first time two cell types that supported HCVpp and HCVcc entry upon ectopic SR-BI expression. Remarkably, the undetectable expression of SR-BI in rat hepatoma cells allowed unambiguous investigation of human SR-BI functions during HCV entry. By expressing different SR-BI mutants in either cell line, our results revealed features of SR-BI intracellular domains that influence HCV infectivity without affecting receptor binding and stimulation of HCV entry induced by HDL/SR-BI interaction. Conversely, we identified positions of SR-BI ectodomain that, by altering HCV binding, inhibit entry. Finally, we characterized alternative ectodomain determinants that, by reducing SR-BI cholesterol uptake and efflux functions, abolish HDL-mediated infection-enhancement. Altogether, we demonstrate that SR-BI is an essential HCV entry factor. Moreover, our results highlight specific SR-BI determinants required during HCV entry and physiological lipid transfer functions hijacked by HCV to favor infection

Private Equity Minority Investments in Large Family Firms: What Influences the Attitude of Family Firm Owners?

This paper extends research in the field of private equity investments in family firms. It contributes to the literature by fundamentally analyzing the decision criteria of family firm owners for using minority investments of private equity investors. This type of financing might be of great interest to family firms, as the family firm owner is able to secure majority ownership and control over the family business. Likewise, minority investments might be attractive for private equity investors, as they are mostly not leveraged and therefore independent from capital market turbulences. Using data from 21 case studies, we identify challenges induced by the family or the business that lead to the phenomenon of private equity minority investments in family firms. We find that perceived benefits and drawbacks of private equity investments are influenced by business and family characteristics. Based on pecking-order theory, resource-based view and the strategy paradigm, propositions as well as a conceptual framework are developed

Genetic indicators of iron limitation in wild populations of \u3cem\u3eThalassiosira oceanica\u3c/em\u3e from the northeast Pacific Ocean

Assessing the iron (Fe) nutritional status of natural diatom populations has proven challenging as physiological and molecular responses can differ in diatoms of the same genus. We evaluated expression of genes encoding flavodoxin (FLDA1) and an Fe-starvation induced protein (ISIP3) as indicators of Fe limitation in the marine diatom Thalassiosira oceanica. The specificity of the response to Fe limitation was tested in cultures grown under Fe- and macronutrient-deficient conditions, as well as throughout the diurnal light cycle. Both genes showed a robust and specific response to Fe limitation in laboratory cultures and were detected in small volume samples collected from the northeast Pacific, demonstrating the sensitivity of this method. Overall, FLDA1 and ISIP3 expression was inversely related to Fe concentrations and offered insight into the Fe nutritional health of T. oceanica in the field. As T. oceanica is a species tolerant to low Fe, indications of Fe limitation in T. oceanica populations may serve as a proxy for severe Fe stress in the overall diatom community. At two shallow coastal locations, FLD1A and ISIP3 expression revealed Fe stress in areas where dissolved Fe concentrations were high, demonstrating that this approach may be powerful for identifying regions where Fe supply may not be biologically available

IRGM Is a Common Target of RNA Viruses that Subvert the Autophagy Network

Autophagy is a conserved degradative pathway used as a host defense mechanism against intracellular pathogens. However, several viruses can evade or subvert autophagy to insure their own replication. Nevertheless, the molecular details of viral interaction with autophagy remain largely unknown. We have determined the ability of 83 proteins of several families of RNA viruses (Paramyxoviridae, Flaviviridae, Orthomyxoviridae, Retroviridae and Togaviridae), to interact with 44 human autophagy-associated proteins using yeast two-hybrid and bioinformatic analysis. We found that the autophagy network is highly targeted by RNA viruses. Although central to autophagy, targeted proteins have also a high number of connections with proteins of other cellular functions. Interestingly, immunity-associated GTPase family M (IRGM), the most targeted protein, was found to interact with the autophagy-associated proteins ATG5, ATG10, MAP1CL3C and SH3GLB1. Strikingly, reduction of IRGM expression using small interfering RNA impairs both Measles virus (MeV), Hepatitis C virus (HCV) and human immunodeficiency virus-1 (HIV-1)-induced autophagy and viral particle production. Moreover we found that the expression of IRGM-interacting MeV-C, HCV-NS3 or HIV-NEF proteins per se is sufficient to induce autophagy, through an IRGM dependent pathway. Our work reveals an unexpected role of IRGM in virus-induced autophagy and suggests that several different families of RNA viruses may use common strategies to manipulate autophagy to improve viral infectivity

Infected erythrocyte-derived extracellular vesicles alter vascular function via regulatory Ago2-miRNA complexes in malaria

Malaria remains one of the greatest public health challenges worldwide, particularly in sub-Saharan Africa. The clinical outcome of individuals infected with Plasmodium falciparum parasites depends on many factors including host systemic inflammatory responses, parasite sequestration in tissues and vascular dysfunction. Production of pro-inflammatory cytokines and chemokines promotes endothelial activation as well as recruitment and infiltration of inflammatory cells, which in turn triggers further endothelial cell activation and parasite sequestration. Inflammatory responses are triggered in part by bioactive parasite products such as hemozoin and infected red blood cell-derived extracellular vesicles (iRBC-derived EVs). Here we demonstrate that such EVs contain functional miRNA-Argonaute 2 complexes that are derived from the host RBC. Moreover, we show that EVs are efficiently internalized by endothelial cells, where the miRNA-Argonaute 2 complexes modulate target gene expression and barrier properties. Altogether, these findings provide a mechanistic link between EVs and vascular dysfunction during malaria infection