Light interception by grain legume row crops

Abstract. Four contrasting grain legume species ( Glycine max, Vigna radiata. Vigna mungo and Vigna angularis ) were grown as row crops with both 0.5 m and 1.0 m spacings between row centres. Light transmission profiles, at ground level, across rows of plants, were obtained for each crop on a number of occasions during growth. The proportion of the incident downward light flux density intercepted by each crop at solar noon was found to be simply and directly related to the product of the proportion of the ground area covered by the crop's leaf canopy and the proportion of the downward light flux density incident at the row centre that was intercepted by the crop. The average proportion of the incident light energy intercepted over the whole day could be related to the proportion intercepted at solar noon.     

Chlamydomonas flagellar outer row dynein assembly protein ODA7 interacts with both outer row and I1 inner row dyneins

We previously found that a mutation at the ODA7 locus in Chlamydomonas prevents axonemal outer row dynein assembly by blocking association of heavy chains and intermediate chains in the cytoplasm. We have now cloned the ODA7 locus by walking in the Chlamydomonas genome from nearby molecular markers, confirmed the identity of the gene by rescuing the mutant phenotype with genomic clones, and identified the ODA7 gene product as a 58-kDa leucine-rich repeat protein unrelated to outer row dynein LC1. Oda7p is missing from oda7 mutant flagella but is present in flagella of other outer row or inner row dynein assembly mutants. However, Oda7 levels are greatly reduced in flagella that lack both outer row dynein and inner row I1 dynein. Biochemical fractionation and rebinding studies support a model in which Oda7 participates in a previously uncharacterized structural link between inner and outer row dyneins.     

Inhibition of IFN-gamma signaling by glucocorticoids

Recent reports suggest that a novel mechanism of glucocorticoid (GC) immunosuppressive action is inhibition of signaling by IL-2 and IL-12, cytokines that use the Janus kinase-STAT signaling pathway. We investigated whether GCs could also block activation of Janus kinase-STAT signaling by IFN-gamma, a potent proinflammatory cytokine. Addition of dexamethasone to PBMC cultures resulted in a dramatic inhibition of IFN-gamma activation of STAT1. Several days of exposure to GCs were required for inhibition of IFN-gamma signaling to become apparent, and the underlying mechanism was down-regulation of STAT1 expression. GCs suppressed the expression of STAT1 mRNA, but did not affect STAT1 protein stability. STAT1 expression and IFN-gamma signaling were preferentially suppressed in macrophages. GCs did not act directly on macrophages, but worked indirectly by regulating macrophage-lymphocyte interactions that control STAT1 expression. GCs inhibited IFN-gamma-inducible gene expression, thus demonstrating the physiological significance of inhibition of signal transduction. Our results identify a novel level of regulation of IFN-gamma signaling, whereby GCs control the amplitude of IFN-gamma signaling by regulating STAT1 expression. These results suggest that inhibition of IFN-gamma signaling contributes to the immunosuppressive action of GCs.     

Signaling by synaptogenic molecules

Multiple signaling pathways initiate and specify the formation of synapses in the central nervous system. General principles that organize nascent synapses have emerged from the studies in multiple model organisms. These include the synapse-organizing roles of dedicated synaptic adhesion molecules, synaptic signaling following receptor-ligand interactions, and the regulation of synapse formation by secreted molecules. Intracellularly, a range of effectors subsequently regulates signaling steps and cytoskeletal changes. Together, a blueprint of synapse formation is emerging into which these distinct signaling steps will need to be integrated temporally and spatially.     

Signaling by the sea

In a spectacular location nestled in the hills on Croatia's coast, a group of 300 scientists from around the world gathered to listen to recent advances in cellular signaling and to gaze across the Adriatic Sea during discussions that surely put this work into perspective. Topics discussed ranged from precise structural details of signaling events to animal models for understanding signaling disorders.     

Modulating Notch signaling by pathway-intrinsic and pathway-extrinsic mechanisms

Despite a relatively simple core-signaling transduction machinery, Notch signaling controls cell differentiation in many different tissues and at multiple stages in a given cell lineage. To understand how Notch generates this multitude of cellular responses, it is important to learn how the Notch-signaling output is modulated at various levels. Pathway-intrinsic as well as pathway-extrinsic mechanisms, including cross-talk between Notch and other major signaling mechanisms, modulate Notch signaling, contributing to the versatile output. In this review, we discuss how Notch signaling is altered in tumors and illustrate the complexity in signaling pathway cross-talk with examples of how Notch synergizes with NF-kappaB signaling and the cellular response to lowered oxygen (hypoxia).     

Non-SH2/PDZ reverse signaling by ephrins

Great strides have been made regarding our understanding of the processes and signaling events influenced by Eph/ephrin signaling that play a role in cell adhesion and cell movement. However, the precise mechanisms by which these signaling events regulate cell and tissue architecture still need further resolution. The Eph/ephrin signaling pathways and the ability to regulate cell-cell adhesion and motility constitutes an impressive system for regulating tissue separation and morphogenesis (Pasquale, 2005, 2008 [1,2]). Moreover, the de-regulation of this signaling system is linked to the promotion of aggressive and metastatic tumors in humans [2]. In the following section, we discuss some of the interesting mechanisms by which ephrins can signal through their own intracellular domains (reverse signaling) either independent of forward signaling or in addition to forward signaling through a cognate receptor. In this review we discuss how ephrins (Eph ligands) "reverse signal" through their intracellular domains to affect cell adhesion and movement, but the focus is on modes of action that are independent of SH2 and PDZ interactions.     

Regulation of Hippo signaling by metabolic pathways in cancer

Hippo signaling is known to maintain balance between cell proliferation and apoptosis via tight regulation of factors, such as metabolic cues, cell-cell contact, and mechanical cues. Cells directly recognize glucose, lipids, and other metabolic cues and integrate multiple signaling pathways, including Hippo signaling, to adjust their proliferation and apoptosis depending on nutrient conditions. Therefore, the dysregulation of the Hippo signaling pathway can promote tumor initiation and progression. Alteration in metabolic cues is considered a major factor affecting the risk of cancer formation and progression. It has recently been shown that the dysregulation of the Hippo signaling pathway, through diverse routes activated by metabolic cues, can lead to cancer with a poor prognosis. In addition, unique crosstalk between metabolic pathways and Hippo signaling pathways can inhibit the effect of anticancer drugs and promote drug resistance. In this review, we describe an integrated perspective of the relationship between the Hippo signaling pathway and metabolic signals in the context of cancer. We also characterize the mechanisms involved in changes in metabolism that are linked to the Hippo signaling pathway in the cancer microenvironment and propose several novel targets for anticancer drug treatment.     

A beta-catenin-independent dorsalization pathway activated by Axin/JNK signaling and antagonized by aida

Axin is a scaffold protein that controls multiple important pathways, including the canonical Wnt pathway and JNK signaling. Here we have identified an Axin-interacting protein, Aida, which blocks Axin-mediated JNK activation by disrupting Axin homodimerization. During investigation of in vivo functions of Axin/JNK signaling and aida in development, it was found that Axin, besides ventralizing activity by facilitating beta-catenin degradation, possesses a dorsalizing activity that is mediated by Axin-induced JNK activation. This dorsalizing activity is repressed when aida is overexpressed in zebrafish embryos. Whereas Aida-MO injection leads to dorsalized embryos, JNK-MO and MKK4-MO can ventralize embryos. The anti-dorsalization activity of aida is conferred by its ability to block Axin-mediated JNK activity. We further demonstrate that dorsoventral patterning regulated by Axin/JNK signaling is independent of maternal or zygotic Wnt signaling. We have thus identified a dorsalization pathway that is exerted by Axin/JNK signaling and its inhibitor Aida during vertebrate embryogenesis.     

MiRNA在TLR信号通路中的负性调控作用

TLR信号是生物体重要的病原体模式识别信号,在免疫识别和炎症反应中具有重要作用,其信号异常会导致许多免疫和炎症相关疾病的发生,因此探讨和明确TLR信号通路的调控机制具有非常重要的意义。近年来研究发现,作为重要的基因表达调控的小分子RNA,微RNA(microRNA,miRNA)能与TLR信号通路中众多靶基因mRNA的3’UTR区结合,从而抑制翻译过程或降解mRNA来发挥负性调控作用。本文就miRNA对TLR信号通路中的一些受体、信号分子、调节因子和细胞因子的负性调控作用方面进行阐述。     

Pathway specificity by the bifunctional receptor frizzled is determined by affinity for wingless

The Frizzled (Fz) protein in Drosophila is a bifunctional receptor that acts through a GTPase pathway in planar polarity signaling and as a receptor for Wingless (Wg) using the canonical Wnt pathway. We found that the ligand-binding domain (CRD) of Fz has an approximately 10-fold lower affinity for Wg than the CRD of DFz2, a Wg receptor without polarity activity. When the Fz CRD is replaced by the high-affinity CRD of DFz2, the resulting chimeric protein gains Wg signaling activity, yet also retains polarity signaling activity. In contrast, the reciprocal exchange of the Fz CRD onto DFz2 is not sufficient to confer polarity activity to DFz2. This suggests that Fz has an intrinsic capacity for polarity signaling and that high-affinity interaction with Wg couples it to the Wnt pathway.     

Signal transfer by Eph receptors

The Eph receptors are a unique family of receptor tyrosine kinases that enforce cellular position in tissues through mainly repulsive signals generated upon cell-cell contact. Together, Eph receptors and their membrane-anchored ligands. the ephrins, are key molecules for establishing tissue organization through signaling pathways that control axonal projection, cell migration, and the maintenance of cellular boundaries. Through their SH2 (Src Homology 2) and PDZ (postsynaptic density protein, disks large, zona occludens) domains, several signaling molecules have been demonstrated to interact with the activated cytoplasmic domain of Eph receptors by using the yeast two-hybrid system and in vitro biochemical assays. Most proteins found to interact with Eph receptors are well-known regulators of cytoskeletal organization and cell adhesion, and also cell proliferation. Promoting growth, however, does not appear to be a primary role of Eph receptors. Explaining which signaling interactions identified for the Eph receptors have physiological significance, how Eph receptor signaling cascades are propagated, and characterizing the intrinsic signaling properties of the ephrins are all exciting questions currently being investigated.     

Subcellular targeting by membrane lipids

The reversible localization of signaling proteins to both the plasma and the internal membranes of cells is critical for the selective activation of downstream functions and depends on interactions with both proteins and membrane lipids. New structural and biochemical analyses of C1, C2, PH, FYVE, FERM and other domains have led to an unprecedented amount of information on the molecular interactions of these signaling proteins with regulatory lipids. A wave of studies using GFP-tagged membrane binding domains as reporters has led to new quantitative insights into the kinetics of these signaling mechanisms.     

Regulation of skeletal myogenesis by Notch

Notch signaling has emerged as a key player in skeletal muscle development and regeneration. Simply stated, Notch signaling inhibits differentiation. Accordingly, fine-tuning the pathway is essential for proper muscle homeostasis. This review will address various aspects of Notch signaling, including our current views of the core pathway, its effects in muscle, its interactions with other signaling pathways, and its relationship with ageing.     

Dynamic control of signaling by modular adaptor proteins

Adaptor proteins are composed exclusively of domains and motifs that mediate molecular interactions, and can thereby link signaling proteins such as activated cell-surface receptors to downstream effectors. Recent data supports the notion that adaptors are not simply coupling devices that hard-wire successive components of signaling pathways. Rather, they display highly dynamic properties that direct the flow of information through signaling networks. The binding activity of adaptors can be regulated by conformational reorganization, and by the cooperative association of domains within the same adaptor. Furthermore, an individual adaptor can deliver different outputs by utilizing distinct combinations of binding partners. Adaptors can also control the oligomerization of receptor signaling complexes, and the subcellular location and duration of signaling events, and act as coincidence detectors to enhance specificity in cellular responses.     

Regulation of signal transduction by endocytosis

Endocytosis of ligand-activated receptors has generally been considered a mechanism to attenuate signaling. There is now a growing body of evidence suggesting that this process is much more sophisticated and that endocytic membrane trafficking regulates both the intensity of signaling and the co-localization of activated receptors with downstream signaling molecules.     

Regulation of Notch signaling by glycosylation

Notch receptors are approximately 300 kDa cell surface glycoproteins whose activation by Notch ligands regulates cell fate decisions in the metazoa. The extracellular domain of Notch receptors has many epidermal growth factor like repeats that are glycosylated with O-fucose and O-glucose glycans as well as N-glycans. Disruption of O-fucose glycan synthesis leads to severe Notch signaling defects in Drosophila and mammals. Removal or addition of O-fucose glycan consensus sites on Notch receptors also leads to Notch signaling defects. Ligand binding and ligand-induced Notch signaling assays have provided insights into how changes in the O-fucose glycans of Notch receptors alter Notch signaling.     

Akt is negatively regulated by Hippo signaling for growth inhibition in Drosophila

Tissue growth is achieved through coordinated cellular growth, cell division and apoptosis. Hippo signaling is critical for monitoring tissue growth during animal development. Loss of Hippo signaling leads to tissue overgrowth due to continuous cell proliferation and block of apoptosis. As cells lacking Hippo signaling are similar in size compared to normal cells, cellular growth must be properly maintained in Hippo signaling-deficient cells. However, it is not clear how Hippo signaling might regulate cellular growth. Here we show that loss of Hippo signaling increased Akt (also called Protein Kinase B, PKB) expression and activity, whereas activation of Hippo signaling reduced Akt expression in developing tissues in Drosophila. While yorkie (yki) is sufficient to increase Akt expression, Akt up-regulation caused by the loss of Hippo signaling is strongly dependent on yki, indicating that Hippo signaling negatively regulates Akt expression through Yki inhibition. Consistently, genetic analysis revealed that Akt plays a critical role in facilitating growth of Hippo signaling-defective tissues. Thus, Hippo signaling not only blocks cell division and promotes apoptosis, but also regulates cellular growth by inhibiting the Akt pathway activity.