p75 neurotrophin receptor is involved in proliferation of undifferentiated mouse embryonic stem cells

Neurotrophins and their receptors are known to play a role in the proliferation and survival of many different cell types of neuronal and non-neuronal lineages. In addition, there is much evidence in the literature showing that the p75 neurotrophin receptor (p75^NTR), alone or in association with members of the family of Trk receptors, is expressed in a wide variety of stem cells, although its role in such cells has not been completely elucidated. In the present work we have investigated the expression of p75^NTR and Trks in totipotent and pluripotent cells, the mouse pre-implantation embryo and embryonic stem and germ cells (ES and EG cells). p75^NTR and TrkA can be first detected in the blastocyst from which ES cell lines are derived. Mouse ES cells retain p75^NTR/TrkA expression. Nerve growth factor is the only neurotrophin able to stimulate ES cell growth in culture, without affecting the expression of stem cell markers, alkaline phosphatase, Oct4 and Nanog. Such proliferation effect was blocked by antagonizing either p75^NTR or TrkA. Interestingly, immunoreactivity to anti-p75^NTR antibodies is lost upon ES cell differentiation. The expression pattern of neurotrophin receptors in murine ES cells differs from human ES cells, that only express TrkB and C, and do not respond to NGF. In this paper we also show that, while primordial germ cells (PGC) do not express p75^NTR, when they are made to revert to an ES-like phenotype, becoming EG cells, expression of p75^NTR is turned on.     

Ethylene action blockade and cold storage affect ripening of ‘Golden’ papaya fruit

The purpose of this work was to evaluate the effects of ethylene action blockade and cold storage on the ripening of ‘Golden’ papaya fruit. Papayas harvested at maturity stage 1 (up to 15% yellow skin) were evaluated. Half of the fruits, whether treated or not treated with 100 nL L⁻¹ of 1-methylcyclopropene (1-MCP), were stored at 23°C, while the other half were stored at 11°C for 20 days prior to being stored at 23°C. Non-refrigerated fruits receiving 1-MCP application presented a reduction in respiratory activity, ethylene production, skin color development and pectinmethylesterase activity. Even with a gradual increase in ethylene production at 23°C, fruits treated with 1-MCP maintained a high firmness, but presented a loss of green skin color. Cold storage caused a decrease in ethylene production when fruits were transferred to 23°C. The results suggest that pulp softening is more dependent on ethylene than skin color development, and that some processes responsible for loss of firmness do not depend on ethylene.     

Carotenoids provide the major antioxidant defence in the globally significant N2-fixing marine cyanobacterium Trichodesmium

Photosynthetic oxygen-evolving microorganisms contend with continuous self-production of molecular oxygen and reactive oxygen species. The deleterious effects of reactive oxygen species are exacerbated for cyanobacterial nitrogen-fixers (diazotrophs) due to the innate sensitivity of nitrogenase to oxygen. This renders incompatible the processes of oxygen-evolving photosynthesis and N-fixation. We examined total antioxidative potential of various diazotrophic and non-diazotrophic cyanobacteria. We focused on Trichodesmium spp., a bloom-forming marine diazotroph that contributes significantly to global nitrogen fixation. Among the species tested, Trichodesmium possessed the highest antioxidant activity. Moreover, while proteins constituted the dominant antioxidative component of all other cyanobacteria tested, Trichodesmium was unique in that small-molecule natural products provided the majority of antioxidant activity, while proteins constituted only 13% of total antioxidant activity. Bioassay-guided fractionation followed by high-performance liquid chromatography profiling of antioxidant purified fractions identified the highly potent antioxidant all- trans -β-carotene, and small amounts of 9- cis -β-carotene and retinyl palmitate. Search of the Trichodesmium genome identified protein sequences homologous to key enzymes in the β-carotene to retinyl palmitate biosynthetic pathway, including 33–37% identity to lecithin retinol acyltransferase. The present study demonstrates the importance of carotenoids in Trichodesmium 's arsenal of defensive compounds against oxidative damage and protection of nitrogenase from oxygen and its radicals.     

Escherichia coli MazF Leads to the Simultaneous Selective Synthesis of Both “Death Proteins” and “Survival Proteins”

The Escherichia coli mazEF module is one of the most thoroughly studied toxin–antitoxin systems. mazF encodes a stable toxin, MazF, and mazE encodes a labile antitoxin, MazE, which prevents the lethal effect of MazF. MazF is an endoribonuclease that leads to the inhibition of protein synthesis by cleaving mRNAs at ACA sequences. Here, using 2D-gels, we show that in E. coli, although MazF induction leads to the inhibition of the synthesis of most proteins, the synthesis of an exclusive group of proteins, mostly smaller than about 20 kDa, is still permitted. We identified some of those small proteins by mass spectrometry. By deleting the genes encoding those proteins from the E. coli chromosome, we showed that they were required for the death of most of the cellular population. Under the same experimental conditions, which induce mazEF-mediated cell death, other such proteins were found to be required for the survival of a small sub-population of cells. Thus, MazF appears to be a regulator that induces downstream pathways leading to death of most of the population and the continued survival of a small sub-population, which will likely become the nucleus of a new population when growth conditions become less stressful.     

Spatial regulation of histidine kinases governing biofilm formation in Bacillus subtilis

Bacillus subtilis is able to form architecturally complex biofilms on solid medium due to the production of an extracellular matrix. A master regulator that controls the expression of the genes involved in matrix synthesis is Spo0A, which is activated by phosphorylation via a phosphorelay involving multiple histidine kinases. Here we report that four kinases, KinA, KinB, KinC, and KinD, help govern biofilm formation but that their contributions are partially masked by redundancy. We show that the kinases fall into two categories and that the members of each pair (one pair comprising KinA and KinB and the other comprising KinC and KinD) are partially redundant with each other. We also show that the kinases are spatially regulated: KinA and KinB are active principally in the older, inner regions of the colony, and KinC and KinD function chiefly in the younger, outer regions. These conclusions are based on the morphology of kinase mutants, real-time measurements of gene expression using luciferase as a reporter, and confocal microscopy using a fluorescent protein as a reporter. Our findings suggest that multiple signals from the older and younger regions of the colony are integrated by the kinases to determine the overall architecture of the biofilm community.     

Genome sequence of Ostreococcus tauri virus OtV-2 throws light on the role of picoeukaryote niche separation in the ocean

Ostreococcus tauri, a unicellular marine green alga, is the smallest known free-living eukaryote and is ubiquitous in the surface oceans. The ecological success of this organism has been attributed to distinct low- and high-light-adapted ecotypes existing in different niches at a range of depths in the ocean. Viruses have already been characterized that infect the high-light-adapted strains. Ostreococcus tauri virus (OtV) isolate OtV-2 is a large double-stranded DNA algal virus that infects a low-light-adapted strain of O. tauri and was assigned to the algal virus family Phycodnaviridae, genus Prasinovirus. Our working hypothesis for this study was that different viruses infecting high- versus low-light-adapted O. tauri strains would provide clues to propagation strategies that would give them selective advantages within their particular light niche. Sequence analysis of the 184,409-bp linear OtV-2 genome revealed a range of core functional genes exclusive to this low-light genotype and included a variety of unexpected genes, such as those encoding an RNA polymerase sigma factor, at least four DNA methyltransferases, a cytochrome b(5), and a high-affinity phosphate transporter. It is clear that OtV-2 has acquired a range of potentially functional genes from its host, other eukaryotes, and even bacteria over evolutionary time. Such piecemeal accretion of genes is a trademark of large double-stranded DNA viruses that has allowed them to adapt their propagation strategies to keep up with host niche separation in the sunlit layers of the oceanic environment.