Signaling Pathways In Animals Research Articles

Evolutionary and Ontogenetic Plasticity of Conserved Signaling Pathways in Animals’ Development

Evolutionary and Ontogenetic Plasticity of Conserved Signaling Pathways in Animals’ Development

Genome-wide analysis of TRAF gene family and its response to bacterial infection in noble scallop Chlamys nobilis with different carotenoids content

Tumor necrosis factor (TNF) receptor-associated factors (TRAFs) are multifunctional adaptor proteins in the immune system, which play significant roles in the regulation of Toll-like receptor and RIG-I-like receptor signaling pathway in animals. Although many TRAF genes have been identified in mollusks, the systematic identification of the TRAF gene family in noble scallop Chlamys nobilis has not been reported, and very little is known about its roles in scallop innate immunity. In this study, four TRAF genes (CnTRAF 2, CnTRAF3, CnTRAF4 and CnTRAF6) were identified and characterized from C. nobilis. Sequence and phylogenetic analysis revealed that CnTRAFs contain typical conserved domains closely related to TRAFs of other mollusks. The motifs analysis of C. nobilis CnTRAFs also showed that the conserved motifs were identical to other mollusks and vertebrates. The expression pattern of CnTRAF genes in tissues of brown and golden scallops (the carotenoid content of golden scallops is significantly higher than that of brown scallops) were not statistically significant, but in hemolymph of scallops challenged with bacteria, the expression of CnTRAF genes was significantly higher than that of control, suggesting that the CnTRAF genes play vital roles in the immunity of mollusks. Furthermore, at several time points after bacteria challenge, the expression level of CnTRAF genes in golden scallops were significantly higher than that of brown scallops, indicating that carotenoids may enhance CnTRAF genes expression and immunity. The systematic analysis of the roles of TRAFs in C. nobilis provides valuable information for the further researches of CnTRAF genes.

Metacaspases versus caspases in development and cell fate regulation.

Initially found to be critically involved in inflammation and apoptosis, caspases have since then been implicated in the regulation of various signaling pathways in animals. How caspases and caspase-mediated processes evolved is a topic of great interest and hot debate. In fact, caspases are just the tip of the iceberg, representing a relatively small group of mostly animal-specific enzymes within a broad family of structurally related cysteine proteases (family C14 of CD clan) found in all kingdoms of life. Apart from caspases, this family encompasses para- and metacaspases, and all three groups of proteases exhibit significant variation in biochemistry and function in vivo. Notably, metacaspases are present in all eukaryotic lineages with a remarkable absence in animals. Thus, metacaspases and caspases must have adapted to operate under distinct cellular and physiological settings. Here we discuss biochemical properties and biological functions of metacaspases in comparison to caspases, with a major focus on the regulation of developmental aspects in plants versus animals.

NCP1/AtMOB1A Plays Key Roles in Auxin-Mediated Arabidopsis Development

MOB1 protein is a core component of the Hippo signaling pathway in animals where it is involved in controlling tissue growth and tumor suppression. Plant MOB1 proteins display high sequence homology to animal MOB1 proteins, but little is known regarding their role in plant growth and development. Herein we report the critical roles of Arabidopsis MOB1 (AtMOB1A) in auxin-mediated development in Arabidopsis. We found that loss-of-function mutations in AtMOB1A completely eliminated the formation of cotyledons when combined with mutations in PINOID (PID), which encodes a Ser/Thr protein kinase that participates in auxin signaling and transport. We showed that atmob1a was fully rescued by its Drosophila counterpart, suggesting functional conservation. The atmob1a pid double mutants phenocopied several well-characterized mutant combinations that are defective in auxin biosynthesis or transport. Moreover, we demonstrated that atmob1a greatly enhanced several other known auxin mutants, suggesting that AtMOB1A plays a key role in auxin-mediated plant development. The atmob1a single mutant displayed defects in early embryogenesis and had shorter root and smaller flowers than wild type plants. AtMOB1A is uniformly expressed in embryos and suspensor cells during embryogenesis, consistent with its role in embryo development. AtMOB1A protein is localized to nucleus, cytoplasm, and associated to plasma membrane, suggesting that it plays roles in these subcellular localizations. Furthermore, we showed that disruption of AtMOB1A led to a reduced sensitivity to exogenous auxin. Our results demonstrated that AtMOB1A plays an important role in Arabidopsis development by promoting auxin signaling.

Structure and function of insulin-like growth factor acid-labile subunits in mammalian homologues

Insulin-like growth factors (IGFs) act as a critical signaling pathway in animals and play significant roles in body growth, development, and occurrence and progression of animal diseases. In the past, structural and functional studies of ligands, receptors and even specific binding proteins in the IGFs system have been extensively investigated. However, the functional study of insulin-like growth factor acid-labile subunit (IGFALS) mainly focused on the prolonging half-life of IGFs. Increasing number of studies indicated that mutations in the IGFALS DNA sequence and low expression level of IGFALS proteins can lead to growth and development retardation in animals. In this review, we summarize recent structural and functional studies of IGFALS in mammals, aiming to further identify detailed genetic mechanism of IGFALS.

Nitrated cyclic GMP modulates guard cell signaling in Arabidopsis.

Nitric oxide (NO) is a ubiquitous signaling molecule involved in diverse physiological processes, including plant senescence and stomatal closure. The NO and cyclic GMP (cGMP) cascade is the main NO signaling pathway in animals, but whether this pathway operates in plant cells, and the mechanisms of its action, remain unclear. Here, we assessed the possibility that the nitrated cGMP derivative 8-nitro-cGMP functions in guard cell signaling. Mass spectrometry and immunocytochemical analyses showed that abscisic acid and NO induced the synthesis of 8-nitro-cGMP in guard cells in the presence of reactive oxygen species. 8-Nitro-cGMP triggered stomatal closure, but 8-bromoguanosine 3',5'-cyclic monophosphate (8-bromo-cGMP), a membrane-permeating analog of cGMP, did not. However, in the dark, 8-bromo-cGMP induced stomatal opening but 8-nitro-cGMP did not. Thus, cGMP and its nitrated derivative play different roles in the signaling pathways that lead to stomatal opening and closure. Moreover, inhibitor and genetic studies showed that calcium, cyclic adenosine-5'-diphosphate-ribose, and SLOW ANION CHANNEL1 act downstream of 8-nitro-cGMP. This study therefore demonstrates that 8-nitro-cGMP acts as a guard cell signaling molecule and that a NO/8-nitro-cGMP signaling cascade operates in guard cells.

Identification of the kinase that activates a nonmetazoan STAT gives insights into the evolution of phosphotyrosine-SH2 domain signaling.

SH2 domains are integral to many animal signaling pathways. By interacting with specific phosphotyrosine residues, they provide regulatable protein-protein interaction domains. Dictyostelium is the only nonmetazoan with functionally characterized SH2 domains, but the cognate tyrosine kinases are unknown. There are no orthologs of the animal tyrosine kinases, but there are very many tyrosine kinase-like kinases (TKLs), a group of kinases which, despite their family name, are classified mainly as serine-threonine kinases. STATs are transcription factors that dimerize via phosphotyrosine-SH2 domain interactions. STATc is activated by phosphorylation on Tyr922 when cells are exposed to the prestalk inducer differentiation inducing factor (DIF-1), a chlorinated hexaphenone. We show that in a null mutant for Pyk2, a tyrosine-specific TKL, exposure to DIF-1 does not activate STATc. Conversely, overexpression of Pyk2 causes constitutive STATc activation. Pyk2 phosphorylates STATc on Tyr922 in vitro and complexes with STATc both in vitro and in vivo. This demonstration that a TKL directly activates a STAT has significant implications for understanding the evolutionary origins of SH2 domain-phosphotyrosine signaling. It also has mechanistic implications. Our previous work suggested that a predicted constitutive STATc tyrosine kinase activity is counterbalanced in vivo by the DIF-1-regulated activity of PTP3, a Tyr922 phosphatase. Here we show that the STATc-Pyk2 complex is formed constitutively by an interaction between the STATc SH2 domain and phosphotyrosine residues on Pyk2 that are generated by autophosphorylation. Also, as predicted, Pyk2 is constitutively active as a STATc kinase. This observation provides further evidence for this highly atypical, possibly ancestral, STAT regulation mechanism.

Arabidopsis MKS1 Is Involved in Basal Immunity and Requires an Intact N-terminal Domain for Proper Function

BackgroundInnate immune signaling pathways in animals and plants are regulated by mitogen-activated protein kinase (MAPK) cascades. MAP kinase 4 (MPK4) functions downstream of innate immune receptors via a nuclear substrate MKS1 to regulate the activity of the WRKY33 transcription factor, which in turn controls the production of anti-microbial phytoalexins.Methodology/Principal FindingsWe investigate the role of MKS1 in basal resistance and the importance of its N- and C-terminal domains for MKS1 function. We used the information that mks1 loss-of-function partially suppresses the mpk4 loss-of-function phenotype, and that transgenic expression of functional MKS1 in mpk4/mks1 double mutants reverted the mpk4 dwarf phenotype. Transformation of mks1/mpk4 with mutant versions of MKS1 constructs showed that a single amino acid substitution in a putative MAP kinase docking domain, MKS1-L32A, or a truncated MKS1 version unable to interact with WRKY33, were deficient in reverting the double mutant to the mpk4 phenotype. These results demonstrate functional requirement in MKS1 for the interaction with MPK4 and WRKY33. In addition, nuclear localization of MKS1 was shown to depend on an intact N-terminal domain. Furthermore, loss-of-function mks1 mutants exhibited increased susceptibility to strains of Pseudomonas syringae and Hyaloperonospora arabidopsidis, indicating that MKS1 plays a role in basal defense responses.ConclusionsTaken together, our results indicate that MKS1 function and subcellular location requires an intact N-terminus important for both MPK4 and WRKY33 interactions.

Innate Immune Signaling Pathways in Animals: Beyond Reductionism

The immune system plays a crucial role in the maintenance of the stability and equilibrium of the internal environment in living organisms. The field of animal innate immunity has been the global focus of immunological research for decades. It is now known that the functions of innate immunity inevitably rely on the action of the molecular machines of the cascades or network of immune signaling pathways. Up to date, many researches on the immune signaling pathways in animals were focused on identifying the component functions or cascade molecules in details, which essentially followed a reductionist paradigm without paying high attention to the integrated features. The main purpose of this article was dedicated to accentuating the shift of this field from a reductionist to a systemic view. First, the former part of this article made efforts to summarize the main aspects of the signaling pathways of animal innate immunity including the web resources, the recapitulation of highlighted pathways, the cross-talks, and the evolutionary considerations, which heavily emphasized the integrated characteristics of the immune signaling pathways. Subsequently, the later part of this article was based on the holistic feature of the immune signaling pathways, mainly dedicated to propose a novel hypothesis. From a whole perspective, the oscillating balance hypothesis was deliberately formulated to characterize the holistic pattern of the signaling transduction network of animal innate immune system, which might help to understand some immunological phenomena through the integral principle of the immune network.

Endogenous morphine synthetic pathway preceded and gave rise to catecholamine synthesis in evolution (Review)

The biological presence and regulatory function of the plant alkaloid morphine in relatively simple and complex integrated animal systems has previously been shown. The pivotal role of dopamine as a chemical intermediate in the morphine biosynthetic pathway in plants establishes a functional basis for its expansion into an essential role as the progenitor catecholamine signaling molecule. In invertebrate neural systems, dopamine serves as the preeminent catecholamine signaling molecule, with the emergence and limited utilization of norepinephrine and its biosynthetic enzyme dopamine beta-hydroxylase in newly defined adaptational chemical circuits required by a rapidly expanding set of physiological demands. In vertebrates, epinephrine emerges as the major end of the catecholamine synthetic pathway consistent with a newly incorporated regulatory modification, i.e. N-methylation of norepinephrine. Given the striking similarities between the enzymatic steps in the morphine biosynthetic pathway and those driving the evolutionary adaptation of catecholamine chemical species to accommodate an expansion of interactive but distinct signaling systems, we surmise that the evolutionary emergence of catecholamine systems required conservation and selective 'retrofit' of specific enzyme activities, i.e. catechol O-methyl transferase and phenylethanol-amine N-methyl transferase, drawn from cellular morphine expression. This hypothesis is further supported by the critical recruitment of enzymatically synthesized tetrahydrobiopterin (BH4) both as an essential cofactor for tyrosine hydroxylase-mediated dopamine production and as a secondary electron donor for nitric oxide synthase-mediated nitric oxide (NO) production. The establishment of a reciprocal regulatory linkage between NO and catecholaminergic processes, as mediated by BH4, subserves a pivotal capacity to promote autocrine and paracrine regulation of signaling molecules. In summary, ongoing development and adaptation of catecholamine signaling pathways in animals appear to be related to their mobile lifestyle associated with complex feeding, sexual and protective processes, which also generate free radicals, thus requiring morphinergic signaling coupling to NO release.

A Proteasome-regulated Glycogen Synthase Kinase-3 Modulates Disease Response in Plants

Glycogen synthase kinase-3 (GSK-3) is a key player in various important signaling pathways in animals. The activity of GSK-3 is known to be modulated by protein phosphorylation and differential complex formation. However, little information is available regarding the function and regulation of plant GSK-3/shaggy-like kinases (GSKs). Analysis of the in vivo kinase activity of MsK1, a GSK from Medicago sativa, revealed that MsK1 is active in healthy plants and that MsK1 activity is down-regulated by the elicitor cellulase in a time- and dose-dependent manner. Surprisingly, cellulase treatment triggered the degradation of the MsK1 protein in a proteasome-dependent manner suggesting a novel mechanism of GSK-3 regulation. Inhibition of MsK1 kinase activity and degradation of the protein were two successive processes that could be uncoupled. In a transgenic approach, stimulus-induced inhibition of MsK1 was impeded by constant replenishment of MsK1 by a strong constitutive promoter. MsK1 overexpressing plants exhibited enhanced disease susceptibility to the virulent bacterial pathogen Pseudomonas syringae. MAP kinase activation in response to pathogen infection was compromised in plants with elevated MsK1 levels. These data strongly suggest that tight regulation of the plant GSK-3, MsK1, may be important for innate immunity to limit the severity of virulent bacterial infection.

Abscisic Acid Signal Transduction: Function of G Protein–Coupled Receptor 1 in Arabidopsis

GTP binding proteins, called G proteins, are important signaling molecules in eukaryotes. Heterotrimeric G proteins, which consist of three subunits, α, β, and γ, make up one of the major classes of G proteins involved in many signaling pathways in animals, including the perception of light, odor

Enzymatic hydrogen atom abstraction from polyunsaturated fatty acids.

The oxidation of polyunsaturated fatty acids such as arachidonic and linoleic acid initiates a plethora of cell signaling pathways in animals and plants. The chemistry of the enzymatic oxidation has been investigated for several enzymes, most notably prostaglandin synthase and the lipoxygenases, revealing many surprises and impressive examples of enzymatic control of hydrogen atom abstraction and subsequent oxygenation.

Life with 25,000 genes.

Life with 25,000 genes.

A Plant 126-kDa Phosphatidylinositol 4-Kinase with a Novel Repeat Structure: CLONING AND FUNCTIONAL EXPRESSION IN BACULOVIRUS-INFECTED INSECT CELLS

Phosphatidylinositol metabolism plays a central role in signaling pathways in animals and is also believed to be of importance in signal transduction in higher plants. We report here the molecular cloning of a cDNA encoding a previously unidentified 126-kDa phosphatidylinositol (PI) 4-kinase (AtPI4Kbeta) from the higher plant Arabidopsis thaliana. The novel protein possesses the conserved domains present in animal and yeast PI 4-kinases, namely a lipid kinase unique domain and a catalytic domain. An additional domain, approximately 300 amino acids long, containing a high percentage (46%) of charged amino acids is specific to this plant enzyme. Recombinant AtPI4Kbeta expressed in baculovirus-infected insect (Spodoptera frugiperda) cells phosphorylated phosphatidylinositol exclusively at the D4 position of the inositol ring. Recombinant protein was maximally activated by 0.6% Triton X-100 but was inhibited by adenosine with an IC50 of approximately 200 microM. Wortmannin at a concentration of 10 microM inhibited AtPI4Kbeta activity by approximately 90%. AtPI4Kbeta transcript levels were similar in all tissues analyzed. Light or treatment with hormones or salts did not change AtPI4Kbeta transcript levels to a great extent, indicating constitutive expression of the AtPI4Kbeta gene.