For T Cell Receptors, Some Breakups Might Not Last Forever

Does the affinity or half-life of peptide-MHC-T cell receptor (TCR) interactions determine T cell activation? In this issue of Immunity, Aleksic et al. (2010) propose a role for the on rate through multiple rebindings to the same TCR

THE 2004 UNITED STATES-AUSTRALIA FREE TRADE AGREEMENT

This note is primarily a short report from Australia on a new bilateral FTA between Australia and the United States (AUSFTA). While it conveys the experience of a very small country, at the other end of the earth, I want to use this example for what it says about the increasingly complex and fluid nature of law making in trans-national commercial law fields like foreign investment and intellectual property. Australia has been a strong supporter of the multilateral trade agreements at the WTO.1 AUSFTA is not Australia’ first bilateral FTA, but it is significant because the partner this time is the strongest of the developed countries. In many ways, the constituents of Australia’s commercial law already reflect the Washington policy consensus. Nonetheless, this agreement with the United States lays down detailed requirements for changes to Australian domestic law. The requirements are not simply a direct translation of United States law. They represent another building block in an edifice of global economic law

Dysregulated RasGRP1 Responds to Cytokine Receptor Input in T Cell Leukemogenesis

Enhanced signaling by the small guanosine triphosphatase Ras is common in T cell acute lymphoblastic leukemia/lymphoma (T-ALL), but the underlying mechanisms are unclear. We identified the guanine nucleotide exchange factor RasGRP1 (Rasgrp1 in mice) as a Ras activator that contributes to leukemogenesis. We found increased RasGRP1 expression in many pediatric T-ALL patients, which is not observed in rare early T cell precursor T-ALL patients with KRAS and NRAS mutations, such as K-Ras[superscript G12D]. Leukemia screens in wild-type mice, but not in mice expressing the mutant K-Ras[superscript G12D] that encodes a constitutively active Ras, yielded frequent retroviral insertions that led to increased Rasgrp1 expression. Rasgrp1 and oncogenic K-Ras[superscript G12D] promoted T-ALL through distinct mechanisms. In K-Ras[superscript G12D] T-ALLs, enhanced Ras activation had to be uncoupled from cell cycle arrest to promote cell proliferation. In mouse T-ALL cells with increased Rasgrp1 expression, we found that Rasgrp1 contributed to a previously uncharacterized cytokine receptor–activated Ras pathway that stimulated the proliferation of T-ALL cells in vivo, which was accompanied by dynamic patterns of activation of effector kinases downstream of Ras in individual T-ALLs. Reduction of Rasgrp1 abundance reduced cytokine-stimulated Ras signaling and decreased the proliferation of T-ALL in vivo. The position of RasGRP1 downstream of cytokine receptors as well as the different clinical outcomes that we observed as a function of RasGRP1 abundance make RasGRP1 an attractive future stratification marker for T-ALL.National Institutes of Health (U.S.). Pioneer AwardNational Cancer Institute (U.S.). Physical Sciences-Oncology Center (U54CA143874)National Institutes of Health (U.S.). (P01 AI091580

Signaling Cascades Modulate the Speed of Signal Propagation through Space

Cells are not mixed bags of signaling molecules. As a consequence, signals must travel from their origin to distal locations. Much is understood about the purely diffusive propagation of signals through space. Many signals, however, propagate via signaling cascades. Here, we show that, depending on their kinetics, cascades speed up or slow down the propagation of signals through space, relative to pure diffusion.We modeled simple cascades operating under different limits of Michaelis-Menten kinetics using deterministic reaction-diffusion equations. Cascades operating far from enzyme saturation speed up signal propagation; the second mobile species moves more quickly than the first through space, on average. The enhanced speed is due to more efficient serial activation of a downstream signaling module (by the signaling molecule immediately upstream in the cascade) at points distal from the signaling origin, compared to locations closer to the source. Conversely, cascades operating under saturated kinetics, which exhibit zero-order ultrasensitivity, can slow down signals, ultimately localizing them to regions around the origin.Signal speed modulation may be a fundamental function of cascades, affecting the ability of signals to penetrate within a cell, to cross-react with other signals, and to activate distant targets. In particular, enhanced speeds provide a way to increase signal penetration into a cell without needing to flood the cell with large numbers of active signaling molecules; conversely, diminished speeds in zero-order ultrasensitive cascades facilitate strong, but localized, signaling

Stochastic Responses May Allow Genetically Diverse Cell Populations to Optimize Performance with Simpler Signaling Networks

Two theories have emerged for the role that stochasticity plays in biological responses: first, that it degrades biological responses, so the performance of biological signaling machinery could be improved by increasing molecular copy numbers of key proteins; second, that it enhances biological performance, by enabling diversification of population-level responses. Using T cell biology as an example, we demonstrate that these roles for stochastic responses are not sufficient to understand experimental observations of stochastic response in complex biological systems that utilize environmental and genetic diversity to make cooperative responses. We propose a new role for stochastic responses in biology: they enable populations to make complex responses with simpler biochemical signaling machinery than would be required in the absence of stochasticity. Thus, the evolution of stochastic responses may be linked to the evolvability of different signaling machineries.National Institutes of Health (U.S.). Pioneer Awar

Digital Signaling and Hysteresis Characterize Ras Activation in Lymphoid Cells

Activation of Ras proteins underlies functional decisions in diverse cell types. Two molecules, RasGRP and SOS, catalyze Ras activation in lymphocytes. Binding of active Ras to SOS' allosteric pocket markedly increases SOS' activity establishing a positive feedback loop for SOS-mediated Ras activation. Integrating in silico and in vitro studies, we demonstrate that digital signaling in lymphocytes (cells are “on” or “off”) is predicated upon feedback regulation of SOS. SOS' feedback loop leads to hysteresis in the dose-response curve, which can enable a capacity to sustain Ras activation as stimuli are withdrawn and exhibit “memory” of past encounters with antigen. Ras activation via RasGRP alone is analog (graded increase in amplitude with stimulus). We describe how complementary analog (RasGRP) and digital (SOS) pathways act on Ras to efficiently convert analog input to digital output. Numerous predictions regarding the impact of our findings on lymphocyte function and development are noted.National Institutes of Health (U.S.). Pioneer AwardNational Institutes of Health (U.S.) (1PO1/AI071195/01

Monovalent engagement of the BCR activates ovalbumin-specific transnuclear B cells

Valency requirements for B cell activation upon antigen encounter are poorly understood. OB1 transnuclear B cells express an IgG1 B cell receptor (BCR) specific for ovalbumin (OVA), the epitope of which can be mimicked using short synthetic peptides to allow antigen-specific engagement of the BCR. By altering length and valency of epitope-bearing synthetic peptides, we examined the properties of ligands required for optimal OB1 B cell activation. Monovalent engagement of the BCR with an epitope-bearing 17-mer synthetic peptide readily activated OB1 B cells. Dimers of the minimal peptide epitope oriented in an N to N configuration were more stimulatory than their C to C counterparts. Although shorter length correlated with less activation, a monomeric 8-mer peptide epitope behaved as a weak agonist that blocked responses to cell-bound peptide antigen, a blockade which could not be reversed by CD40 ligation. The 8-mer not only delivered a suboptimal signal, which blocked subsequent responses to OVA, anti-IgG, and anti-kappa, but also competed for binding with OVA. Our results show that fine-tuning of BCR-ligand recognition can lead to B cell nonresponsiveness, activation, or inhibition

Métodos multivariados aplicados ao melhoramento genético do feijoeiro visando ao aumento da tolerância ao estresse osmótico e biofortificação de grãos

O feijoeiro (Phaseolus vulgaris L.) é uma cultura agrícola muito importante economicamente e nutricionalmente para a população brasileira e necessita de metodologias simples e eficazes que auxiliem o processo de melhoramento genético. As técnicas empregadas devem minimizar os efeitos indesejáveis da multicolinearidade entre as características estudadas durante o processo de seleção. A produção de sementes de feijão, normalmente, é limitada pela escassez hídrica e solos salinos. No entanto, devido a grande variabilidade genética, característica da espécie, é possível encontrar materiais genéticos mais tolerantes a esses estresses osmóticos. A germinação e o desenvolvimento inicial da plântula são fases críticas e desta maneira é importante selecionar os matérias genéticos mais tolerantes nestas fases. Além de selecionar genótipos tolerantes é necessário selecionar materiais genéticos que sejam ricos nutricionalmente, principalmente, em relação à composição mineralógica. Os principais objetivos almejados com este trabalho foram reduzir a multicolinearidade e selecionar genótipos para a tolerância ao estresse osmótico e a biofortificação dos grãos do feijoeiro, com base nos valores genéticos. Desta maneira, foram utilizadas duas técnicas para reduzir a influência da multicolinearidade: o descarte de variáveis redundantes pelas variáveis canônicas, e o uso das análises de fatores para reduzir o número de variáveis. As variáveis analisadas foram: porcentagem de germinação e de plântulas normais, tempo médio de germinação, índice de velocidade de germinação, comprimentos de raiz e de hipocótilo, massas seca de raiz e da parte aérea, razão raiz/parte aérea e o produto da porcentagem de plântulas normais pelo comprimento das plântulas. Avaliou-se também a composição mineralógica dos grãos em relação à concentração de cálcio, ferro, zinco, potássio, magnésio, manganês e fósforo. Adicionalmente, para estimar os parâmetros e os valores genéticos realizou-se análise via modelos mistos, utilizando-se a técnica de REML/BLUP. Os genótipos foram selecionados com base da média genética, estabilidade e adaptabilidade, utilizando-se a técnica da média harmônica da performance relativa dos valores genéticos. Os genótipos que apresentaram as maiores tolerâncias, adaptabilidade e estabilidade quanto aos estresses osmóticos foram: CNFC 15466, CNFC 15462, CNFC 15630, BRS Valente, Capixaba Precoce, CNFP 15290, CNFP 15292 e CNFP 15302. Enquanto os genótipos mais ricos e divergentes geneticamente do grupo comercial carioca foram: CNFC 15475 e CNFC 15625, e do grupo comercial preto foram: CNFP 15310 e CNFP 15304. Conclui-se que a utilização de técnicas multivariadas facilita a seleção de genótipos promissores como parentais na formação de linhagens tolerantes ao estresse osmótico e biofortificados. Palavras-chave: feijoeiro comum; seleção de genótipos; estresse hídrico e salino; multicolinearidade; composição mineral

Population Health Metrics Research Consortium gold standard verbal autopsy validation study: design, implementation, and development of analysis datasets

Background: Verbal autopsy methods are critically important for evaluating the leading causes of death in populations without adequate vital registration systems. With a myriad of analytical and data collection approaches, it is essential to create a high quality validation dataset from different populations to evaluate comparative method performance and make recommendations for future verbal autopsy implementation. This study was undertaken to compile a set of strictly defined gold standard deaths for which verbal autopsies were collected to validate the accuracy of different methods of verbal autopsy cause of death assignment.Methods: Data collection was implemented in six sites in four countries: Andhra Pradesh, India; Bohol, Philippines; Dar es Salaam, Tanzania; Mexico City, Mexico; Pemba Island, Tanzania; and Uttar Pradesh, India. The Population Health Metrics Research Consortium (PHMRC) developed stringent diagnostic criteria including laboratory, pathology, and medical imaging findings to identify gold standard deaths in health facilities as well as an enhanced verbal autopsy instrument based on World Health Organization (WHO) standards. A cause list was constructed based on the WHO Global Burden of Disease estimates of the leading causes of death, potential to identify unique signs and symptoms, and the likely existence of sufficient medical technology to ascertain gold standard cases. Blinded verbal autopsies were collected on all gold standard deaths.Results: Over 12,000 verbal autopsies on deaths with gold standard diagnoses were collected (7,836 adults, 2,075 children, 1,629 neonates, and 1,002 stillbirths). Difficulties in finding sufficient cases to meet gold standard criteria as well as problems with misclassification for certain causes meant that the target list of causes for analysis was reduced to 34 for adults, 21 for children, and 10 for neonates, excluding stillbirths. To ensure strict independence for the validation of methods and assessment of comparative performance, 500 test-train datasets were created from the universe of cases, covering a range of cause-specific compositions.Conclusions: This unique, robust validation dataset will allow scholars to evaluate the performance of different verbal autopsy analytic methods as well as instrument design. This dataset can be used to inform the implementation of verbal autopsies to more reliably ascertain cause of death in national health information systems