Eltrombopag for the Treatment of Refractory Pure RBC Aplasia after Major ABO Incompatible Hematopoietic Stem Cell Transplantation

Pure RBC aplasia (PRCS) is a well-recognized complication after allogeneic hematopoietic stem cell transplantation (HSCT). Many therapeutic options are available to treat this condition, including erythropoietin, rituximab, bortezomib, plasma exchange, immunoadsorption, donor lymphocyte infusion, mesenchymal stem cells, antithymocyte globulin, and high-dose steroids; however, treatment outcomes are often variable and can sometimes lead to disappointing results. In this brief article we report our experience with 2 patients with PRCA after major ABO-incompatible HSCT who were resistant to multiple therapeutic interventions and who eventually benefited from treatment with eltrombopag, a thrombopoietin mimetic approved by the US Food and Drug Administration for the treatment of patients with immune thrombocytopenic purpura or severe aplastic anemia refractory to immunosuppressive agents or not eligible for HSCT. Data from these 2 patients show that eltrombopag was effective in treating erythroid aplasia and transfusion dependence after HSCT in patients who did not benefit from multiple previous treatments. Moreover, eltrombopag was well tolerated, with only a transient thrombocytosis requiring dose adjustment and no evidence of clonal evolution. Based on the positive results obtained in these 2 patients, we suggest that eltrombopag may have a favorable effect on unilineage cytopenias such as PRCA. Further studies in a large proportion of patients are mandatory to confirm these preliminary results.     

Seasonal fluxes of carbonyl sulfide in a midlatitude forest

Carbonyl sulfide (OCS), the most abundant sulfur gas in the atmosphere, has a summer minimum associated with uptake by vegetation and soils, closely correlated with CO₂. We report the first direct measurements to our knowledge of the ecosystem flux of OCS throughout an annual cycle, at a mixed temperate forest. The forest took up OCS during most of the growing season with an overall uptake of 1.36 ± 0.01 mol OCS per ha (43.5 ± 0.5 g S per ha, 95% confidence intervals) for the year. Daytime fluxes accounted for 72% of total uptake. Both soils and incompletely closed stomata in the canopy contributed to nighttime fluxes. Unexpected net OCS emission occurred during the warmest weeks in summer. Many requirements necessary to use fluxes of OCS as a simple estimate of photosynthesis were not met because OCS fluxes did not have a constant relationship with photosynthesis throughout an entire day or over the entire year. However, OCS fluxes provide a direct measure of ecosystem-scale stomatal conductance and mesophyll function, without relying on measures of soil evaporation or leaf temperature, and reveal previously unseen heterogeneity of forest canopy processes. Observations of OCS flux provide powerful, independent means to test and refine land surface and carbon cycle models at the ecosystem scale.Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere (1), and biogeochemical cycling of OCS affects both the stratosphere and the troposphere. The tropospheric OCS mixing ratio is between 300 and 550 parts per trillion (ppt) (1) (10⁻¹² mol OCS per mol dry air), decreasing sharply with altitude in the stratosphere (2). In times of low volcanic activity, the sulfur budget and aerosol loading of the stratosphere are largely controlled by transport and photooxidation of OCS from the troposphere (3). The processes regulating emission and uptake of OCS are thus important factors in determining how changes in climate and land cover may affect the stratospheric sulfate layer.Oceans are the dominant source of atmospheric OCS (4), with smaller emissions from anthropogenic and terrestrial sources, such as wetlands and anoxic soils (e.g., refs. 5 and 6) and oxic soils during times of heat or drought stress (e.g., refs. 7 and 8). The terrestrial biosphere is the largest sink for OCS (1, 4, 9, 10) with uptake by both oxic soils (e.g., ref. 11) and vegetation (e.g., ref. 9). Once OCS molecules pass through the stomata of leaves, the uptake rate of OCS is controlled by reaction with carbonic anhydrase (CA) within the mesophyll, to produce H₂S and CO₂. CA is the same enzyme that hydrolyzes carbon dioxide (CO₂) in the first chemical step of photosynthesis (12).Studies considering the large-scale atmospheric variability of OCS have linked OCS fluxes and the photosynthetic uptake of CO₂ for regional and global scales (1, 4, 13). Leaf-scale studies have confirmed the OCS link to photosynthesis (14, 15). Initial OCS ecosystem flux estimations were made using flask sampling followed by analysis via gas chromatography–mass spectrometry (GC-MS) (13, 16), but these studies did not have sufficient resolution to examine daily or hourly controls on the OCS flux. Laser spectrometers have been developed (17, 18) to enable direct, in situ measurement of OCS fluxes by eddy covariance, and measurements of OCS ecosystem fluxes have been reported, for periods of up to a few weeks, above arid forests (19) and an agricultural field (8, 20).Net carbon exchange in terrestrial ecosystems [net ecosystem exchange (NEE)] can be measured by eddy flux methods. NEE may be regarded as the sum of two gross fluxes: gross ecosystem productivity (GEP) and ecosystem respiration (R_eco). GEP is the light-dependent part of NEE, estimated by subtracting daytime ecosystem respiration (R_eco), computed by extrapolation of the temperature dependence of nighttime NEE (NEE – R_eco = GEP) (e.g., refs. 21–24). At night, NEE includes all autotrophic and heterotrophic respiration processes. During the day, GEP approximates the carboxylation rate minus photorespiration at the ecosystem scale (25). Extrapolation of nighttime R_eco introduces major uncertainty in the interpretation of GEP, which could be reduced, and the ecological significance of GEP increased, by developing independent methods of measuring rates of photosynthetic processes. As shown below, fluxes of OCS give more direct information on one of the major controls on GEP, stomatal conductance, rather than GEP itself, providing a powerful means for testing and improving ecosystem models and for scaling up leaf-level processes to the whole ecosystem.Here we describe the factors controlling the hourly, daily, seasonal, and total fluxes of OCS in a forest ecosystem, using a year (2011) of high-frequency, direct measurements at Harvard Forest, MA. We report the seasonal cycle, the response to environmental conditions, and the total deposition flux of OCS throughout the year 2011. We compare these fluxes to corresponding measurements of CO₂ flux and to simulations using the Simple Biosphere model (SiB3).     

From the Cover: PNAS Plus: The essential gene set of a photosynthetic organism

Synechococcus elongatus PCC 7942 is a model organism used for studying photosynthesis and the circadian clock, and it is being developed for the production of fuel, industrial chemicals, and pharmaceuticals. To identify a comprehensive set of genes and intergenic regions that impacts fitness in S. elongatus, we created a pooled library of ∼250,000 transposon mutants and used sequencing to identify the insertion locations. By analyzing the distribution and survival of these mutants, we identified 718 of the organism’s 2,723 genes as essential for survival under laboratory conditions. The validity of the essential gene set is supported by its tight overlap with well-conserved genes and its enrichment for core biological processes. The differences noted between our dataset and these predictors of essentiality, however, have led to surprising biological insights. One such finding is that genes in a large portion of the TCA cycle are dispensable, suggesting that S. elongatus does not require a cyclic TCA process. Furthermore, the density of the transposon mutant library enabled individual and global statements about the essentiality of noncoding RNAs, regulatory elements, and other intergenic regions. In this way, a group I intron located in tRNA^Leu, which has been used extensively for phylogenetic studies, was shown here to be essential for the survival of S. elongatus. Our survey of essentiality for every locus in the S. elongatus genome serves as a powerful resource for understanding the organism’s physiology and defines the essential gene set required for the growth of a photosynthetic organism.Determining the sets of genes necessary for survival of diverse organisms has helped to identify the fundamental processes that sustain life across an array of environments (1). This research has also served as the starting point for efforts by synthetic biologists to design organisms from scratch (2, 3). Despite the importance of essential gene sets, they have traditionally been challenging to gather because of the difficulty of observing mutations that result in lethal phenotypes. More recently, the pairing of transposon mutagenesis with next generation sequencing, referred to collectively as transposon sequencing (Tn-seq), has resulted in a dramatic advance in the identification of essential gene sets (4–7). The key characteristic of Tn-seq is the use of high-throughput sequencing to screen for the fitness of every transposon mutant in a pooled population to measure each mutation’s impact on survival. These data can be used to quantitatively ascertain the effect of loss-of-function mutations at any given locus, intragenic or intergenic, in the conditions under which the library is grown (8). Essential gene sets for 42 diverse organisms distributed across all three domains have now been defined, largely through the use of Tn-seq (9). A recently developed variation on Tn-seq, random barcode transposon site sequencing (RB-TnSeq) (10), further minimizes the library preparation and sequencing costs of whole-genome mutant screens.Despite the proliferation of genome-wide essentiality screens, a complete essential gene set has yet to be defined for a photosynthetic organism. A collection of phenotyped Arabidopsis thaliana mutants has been created but extends to only one-tenth of Arabidopsis genes (11). In algae, efforts are underway to produce a Tn-seq–like system in Chlamydomonas reinhardtii; however, the mutant library currently lacks sufficient saturation to determine gene essentiality (12). To date, the essential genes for photoautotrophs have only been estimated by indirect means, such as by comparative genomics (13). The absence of experimentally determined essential gene sets in photosynthetic organisms, despite their importance to the environment and industrial production, is largely because of the difficulty and time required for genetic modification of these organisms.Cyanobacteria comprise an extensively studied and ecologically important photosynthetic phylum. They are responsible for a large portion of marine primary production and have played a foundational role in research to decipher the molecular components of photosynthesis (14, 15). Synechococcus elongatus PCC 7942 is a particularly well-studied member of this phylum because of its genetic tractability and streamlined genome (16). As a result, it has been developed as a model photosynthetic organism and a production platform for a number of fuel products and high-value chemicals (17). Despite the importance of S. elongatus for understanding photosynthesis and industrial production, 40% of its genes have no functional annotation, and only a small portion of those that do have been studied experimentally.Here, we use RB-TnSeq, a method that pairs high-density transposon mutagenesis and pooled mutant screens, to probe the S. elongatus genome for essential genes and noncoding regions. We categorized 96% of 2,723 genes in S. elongatus as either essential (lethal when mutated), beneficial (growth defect when mutated), or nonessential (no phenotype when mutated) under standard laboratory conditions. Furthermore, we determined the genome-wide essentiality of noncoding RNAs (ncRNAs), regulatory regions, and intergenic regions. Our investigation has produced an extensive analysis of the loci essential for the growth of a photosynthetic organism and developed a powerful genomic tool that can be used for additional screens under a wide array of ecologically and industrially relevant growth conditions.     

Factors Influencing Improvement of Trauma-Related Symptoms Among Somali Refugee Youth in Urban Kenya

Somali refugee youth present with a heightened risk for common mental disorders (CMDs), and yet few studies have discussed factors influencing mental health outcomes after psychosocial interventions. This study aimed to identify key factors that contribute to the improvement of CMD symptoms among Somali youth displaced in urban Kenya. Logistic regression analyses revealed that trauma exposure and emotional coping predict overall symptom improvement, pointing to a differential intervention effect on those with differing levels of religious belief and attitudes toward violence. This study provides insights into how psychosocial factors likely contribute to positive intervention outcomes in Somali refugee youth.

     

Developmental Trajectories of Delinquent and Aggressive Behavior: Evidence for Differential Heritability

Child Psychiatry & Human Development - The developmental course of antisocial behavior is often described in terms of qualitatively distinct trajectories. However, the genetic etiology of...