Chloroplast envelope membranes: a dynamic interface between plastids and the cytosol

Chloroplasts are bounded by a pair of outer membranes, the envelope, that is the only permanent membrane structure of the different types of plastids. Chloroplasts have had a long and complex evolutionary past and integration of the envelope membranes in cellular functions is the result of this evolution. Plastid envelope membranes contain a wide diversity of lipids and terpenoid compounds serving numerous biochemical functions and the flexibility of their biosynthetic pathways allow plants to adapt to fluctuating environmental conditions (for instance phosphate deprivation). A large body of knowledge has been generated by proteomic studies targeted to envelope membranes, thus revealing an unexpected complexity of this membrane system. For instance, new transport systems for metabolites and ions have been identified in envelope membranes and new routes for the import of chloroplast-specific proteins have been identified. The picture emerging from our present understanding of plastid envelope membranes is that of a key player in plastid biogenesis and the co-ordinated gene expression of plastid-specific protein (owing to chlorophyll precursors), of a major hub for integration of metabolic and ionic networks in cell metabolism, of a flexible system that can divide, produce dynamic extensions and interact with other cell constituents. Envelope membranes are indeed one of the most complex and dynamic system within a plant cell. In this review, we present an overview of envelope constituents together with recent insights into the major functions fulfilled by envelope membranes and their dynamics within plant cells. Special Issue of Photosynthesis Research in honor of Andrew A. Benson.     

Miscanthus Clones Display Large Variation in Floral Biology and Different Environmental Sensitivities Useful for Breeding

A wider range of Miscanthus varieties is required to develop Miscanthus clones that are suitable for bioenergy production. For this reason, breeding programs need to be initiated using knowledge regarding the genetic influence on floral biological traits. The objective of the present study was to characterize the genotypic variation in flowering and panicle architecture traits in Miscanthus by studying (i) the clone effect on these traits and (ii) the clone sensitivity to environmental conditions. The flowering traits characterized were date of panicle emergence, date of flowering onset, and interval between these two traits. The panicle architecture traits characterized were total panicle length, longest panicle raceme size, raceme number per panicle, floral density, and total flower number per panicle. Eight clones were studied in a greenhouse under four environmental conditions including two day lengths (an 8-h short day length and a natural day length) and two temperature treatments (warm and cool). Miscanthus clones showed large differences in flowering and panicle architecture traits. Moreover, day length appeared to be the most important environmental factor creating differential clone sensitivities for the panicle emergence and the onset of flowering in contrast to temperature factor for the total flower number per panicle. In addition, the behavior of the clone Sacc was in contrast with that of the other clones for most of the traits studied. This knowledge will be useful to optimize the synchronization of flowering between Miscanthus clones for more successful breeding programs.     

Three-dimensional electron microscopy analysis of ndc10-1 mutant reveals an aberrant organization of the mitotic spindle and spindle pole body defects in Saccharomyces cerevisiae

Kinetochore components play a major role in regulating the transmission of genetic information during cell division. Ndc10p, a kinetochore component of the essential CBF3 complex in budding yeast is required for chromosome attachment to the mitotic spindle. ndc10-1 mutant was shown to display chromosome mis-segregation as well as an aberrant mitotic spindle (Goh and Kilmartin, 1993). In addition, Ndc10p localizes along the spindle microtubules (Muller-Reichert et al., 2003). To further understand the role of Ndc10p in the mitotic apparatus, we performed a three-dimensional electron microscopy (EM) reconstruction of mitotic spindles from serial sections of cryo-immobilized ndc10-1 mutant cells. This analysis reveals a dramatic reduction in the number of microtubules present in the half-spindle, which is connected to the newly formed spindle pole body (SPB) in ndc10-1 cells. Moreover, in contrast to wild-type (WT) cells, ndc10-1 cells showed a significantly lower signal intensity of the SPB components Spc42p and Spc110p fused with GFP, in mother cell bodies compared with buds. A subsequent EM analysis also showed clear defects in the newly formed SPB, which remains in the mother cell during anaphase. These results suggest that Ndc10p is required for maturation of the newly formed SPB. Intriguingly, mutations in other kinetochore components, ndc80-1 and spc24-1, showed kinetochore detachment from the spindle, similar to ndc10-1, but did not display defects in SPBs. This suggests that unattached kinetochores are not sufficient to cause SPB defects in ndc10-1 cells. We propose that Ndc10p, alongside its role in kinetochore–microtubule interaction, is also essential for SPB maturation and mitotic spindle integrity.     

Production of biologically active forms of recombinant hepcidin, the iron-regulatory hormone

Hepcidin is a liver produced cysteine-rich peptide hormone that acts as the central regulator of body iron metabolism. Hepcidin is synthesized under the form of a precursor, prohepcidin, which is processed to produce the biologically active mature 25 amino acid peptide. This peptide is secreted and acts by controlling the concentration of the membrane iron exporter ferroportin on intestinal enterocytes and macrophages. Hepcidin binds to ferroportin, inducing its internalization and degradation, thus regulating the export of iron from cells to plasma. The aim of the present study was to develop a novel method to produce human and mouse recombinant hepcidins, and to compare their biological activity towards their natural receptor ferroportin. Hepcidins were expressed in Escherichia coli as thioredoxin fusion proteins. The corresponding peptides, purified after cleavage from thioredoxin, were properly folded and contained the expected four-disulfide bridges without the need of any renaturation or oxidation steps. Human and mouse hepcidins were found to be biologically active, promoting ferroportin degradation in macrophages. Importantly, biologically inactive aggregated forms of hepcidin were observed depending on purification and storage conditions, but such forms were unrelated to disulfide bridge formation.     

Laboratory monitoring of patients treated with antihypertensive drugs and newly exposed to non steroidal anti-inflammatory drugs: a cohort study

Background

Drug-Drug Interactions between Non Steroidal Anti-Inflammatory Drugs (NSAIDs) and Angiotensin Converting Enzyme Inhibitors (ACEIs), Angiotensin Receptor Blocker (ARBs) or diuretics can lead to renal failure and hyperkalemia. Thus, monitoring of serum creatinine and potassium is recommended when a first dispensing of NSAID occur in patients treated with these drugs.

Methods

We conducted a pharmacoepidemiological retrospective cohort study using data from the French Health Insurance Reimbursement Database to evaluate the proportion of serum creatinine and potassium laboratory monitoring in patients treated with ACEI, ARB or diuretic and receiving a first dispensing of NSAID. We described the first dispensing of NSAID among 3,500 patients of a 4-year cohort (6,633 patients treated with antihypertensive drugs) and analyzed serum creatinine and potassium laboratory monitoring within the 3 weeks after the first NSAID dispensing.

Results

General Practitioners were the most frequent prescribers of NSAIDs (85.5%, 95% CI: 84.3–86.6). The more commonly prescribed NSAIDs were ibuprofen (20%), ketoprofen (15%), diclofenac (15%) and piroxicam (12%). Serum creatinine and potassium monitoring was 10.7% (95% CI: 9.5–11.8) in patients treated by ACEIs, ARBs or diuretics. Overall, monitoring was more frequently performed to women aged over 60, treated with digoxin or glucose lowering drugs, but not to patients treated with ACEIs, ARBs or diuretics. Monitoring was more frequent when NSAIDs'' prescribers were cardiologists or anesthesiologists.

Conclusion

Monitoring of serum creatinine and potassium of patients treated with ACEIs, ARBs or diuretics and receiving a first NSAID dispensing is insufficiently performed and needs to be reinforced through specific interventions.     

The RON2-AMA1 interaction is a critical step in moving junction-dependent invasion by apicomplexan parasites

Obligate intracellular Apicomplexa parasites share a unique invasion mechanism involving a tight interaction between the host cell and the parasite surfaces called the moving junction (MJ). The MJ, which is the anchoring structure for the invasion process, is formed by secretion of a macromolecular complex (RON2/4/5/8), derived from secretory organelles called rhoptries, into the host cell membrane. AMA1, a protein secreted from micronemes and associated with the parasite surface during invasion, has been shown in vitro to bind the MJ complex through a direct association with RON2. Here we show that RON2 is inserted as an integral membrane protein in the host cell and, using several interaction assays with native or recombinant proteins, we define the region that binds AMA1. Our studies were performed both in Toxoplasma gondii and Plasmodium falciparum and although AMA1 and RON2 proteins have diverged between Apicomplexa species, we show an intra-species conservation of their interaction. More importantly, invasion inhibition assays using recombinant proteins demonstrate that the RON2-AMA1 interaction is crucial for both T. gondii and P. falciparum entry into their host cells. This work provides the first evidence that AMA1 uses the rhoptry neck protein RON2 as a receptor to promote invasion by Apicomplexa parasites.     

Hypoxia in the St. Lawrence Estuary: How a Coding Error Led to the Belief that “Physics Controls Spatial Patterns”

Two fundamental sign errors were found in a computer code used for studying the oxygen minimum zone (OMZ) and hypoxia in the Estuary and Gulf of St. Lawrence. These errors invalidate the conclusions drawn from the model, and call into question a proposed mechanism for generating OMZ that challenges classical understanding. The study in question is being cited frequently, leading the discipline in the wrong direction.     

Meridianins, a new family of protein kinase inhibitors isolated from the ascidian Aplidium meridianum

Meridianins are brominated 3-(2-aminopyrimidine)-indoles which are purified from Aplidium meridianum, an Ascidian from the South Atlantic (South Georgia Islands). We here show that meridianins inhibit various protein kinases such as cyclin-dependent kinases, glycogen synthase kinase-3, cyclic nucleotide-dependent kinases and casein kinase 1. Meridianins prevent cell proliferation and induce apoptosis, a demonstration of their ability to enter cells and to interfere with the activity of kinases important for cell division and cell death. These results suggest that meridianins constitute a promising scaffold from which more potent and selective protein kinase inhibitors could be designed.