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Other Signalling Pathways (other + signalling_pathway)
Selected AbstractsStomatal responses to CO2 during a diel Crassulacean acid metabolism cycle in Kalanchoe daigremontiana and Kalanchoe pinnataPLANT CELL & ENVIRONMENT, Issue 5 2009SUSANNE VON CAEMMERER ABSTRACT To investigate the diurnal variation of stomatal sensitivity to CO2, stomatal response to a 30 min pulse of low CO2 was measured four times during a 24 h time-course in two Crassulacean acid metabolism (CAM) species Kalanchoe daigremontiana and Kalanchoe pinnata, which vary in the degree of succulence, and hence, expression and commitment to CAM. In both species, stomata opened in response to a reduction in pCO2 in the dark and in the latter half of the light period, and thus in CAM species, chloroplast photosynthesis is not required for the stomatal response to low pCO2. Stomata did not respond to a decreased pCO2 in K. daigremontiana in the light when stomata were closed, even when the supply of internal CO2 was experimentally reduced. We conclude that stomatal closure during phase III is not solely mediated by high internal pCO2, and suggest that in CAM species the diurnal variability in the responsiveness of stomata to pCO2 could be explained by hypothesizing the existence of a single CO2 sensor which interacts with other signalling pathways. When not perturbed by low pCO2, CO2 assimilation rate and stomatal conductance were correlated both in the light and in the dark in both species. [source] Calmodulin activity and cAMP signalling modulate growth and apical secretion in pollen tubesTHE PLANT JOURNAL, Issue 6 2004Cláudia Rato Summary Our present understanding implicates both calmodulin (CaM) and 3,,5,-cyclicAMP (cAMP) in the regulation of pollen tube growth. However, downstream molecules of these signalling pathways and the cellular processes they modulate remain largely unknown. In order to elucidate the role of CaM, we mapped its activity in growing pollen tubes. 2-chloro-(,-amino-Lys75)-[6-4-(N,N, -diethylaminophenyl)-1,3,5-triazin-4-yl]-calmodulin (TA-CaM) and fluorescein-calmodulin (FL-CaM), fluorescent analogues of CaM, were loaded into pollen tubes and CaM activity was mapped by fluorescence ratio imaging. It was found that CaM activity exhibits a tip-focused gradient, similar to the distribution of cytosolic-free calcium ([Ca2+]c). In long pollen tubes, apical CaM activity was also found to oscillate with a period similar to [Ca2+]c (40,80 sec). This oscillatory behaviour was not observed in small pollen tubes or in tubes that had stopped growing. Changes in CaM activity within the dome of the pollen tube apex resulting from the photolysis of caged photolysis of RS-20 (a peptide antagonist of CaM) induced re-orientation of the growth axis, suggesting that CaM is also involved in the guidance mechanism. CaM activity was strongly modulated by intracellular changes in cAMP (induced by activators and antagonists of adenylyl cyclase). These results indicate that the action of this protein is dependent not solely on [Ca2+]c but also on a cross-talk with other signalling pathways. A putative target of this cross-talk is the secretory machinery as observed in pollen tubes loaded with the FM (N -(3-triethylammoniumpropyl)-4-(4-dibutylamino)styryl)pyridinium dibromide 1-43 dye and exposed to different antagonists and activators of these molecules. Our data thus suggest that pollen tube growth and orientation depend on an intricate cross-talk between multiple signalling pathways in which CaM is a key element. [source] Molecular Characterization of the NCoA-1,STAT,6 InteractionCHEMBIOCHEM, Issue 8 2008Markus Seitz Abstract Many protein,protein interactions involved in cell signalling, cell adhesion and regulation of transcription are mediated by short ,-helical recognition motifs with the sequence Leu-Xaa-Xaa-Leu-Leu (LXXLL, where Xaa is any amino acid). Originally observed in cofactors that interact with hormone-activated nuclear receptors, LXXLL motifs are now known to occur in many transcription factors, including the STAT family, which transmit signals from activated cytokine receptors at the cell surface to target genes in the nucleus. STAT,6 becomes activated in response to IL-4 and IL-13, which regulate immune and anti-inflammatory responses. Structural studies have revealed how an LXXLL motif located in 2.5 turns of an ,-helical peptide derived from STAT,6 provide contacts through the leucine side chains to the coactivator of transcription, NCoA-1. However, since many protein,protein interactions are mediated by LXXLL motifs, it is important to understand how specificity is achieved in this and other signalling pathways. Here, we show that energetically important contacts between STAT,6 and NCoA-1 are made in residues that flank the LXXLL motif, including the underlined residues in the sequence LLPPTEQDLTKLL. We also demonstrate how the affinity for NCoA-1 of peptides derived from this region of STAT,6 can be significantly improved by optimising knobs-into-holes contacts on the surface of the protein. The results provide important new insights into the origins of binding specificity, and might be of practical value in the design of novel small-molecule inhibitors of this important protein,protein interaction. [source] CHARACTERIZATION OF THE ACUTE CARDIOVASCULAR EFFECTS OF INTRAVENOUSLY ADMINISTERED INSULIN-LIKE GROWTH FACTOR-I IN CONSCIOUS SPRAGUE-DAWLEY RATSCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 12 2006Nga Cao SUMMARY 1Insulin-like growth factor (IGF)-I has acute effects on cardiovascular function, including a well-characterized vasodilator response in isolated arteries. In addition to increasing the release of nitric oxide, IGF-I also has effects on a variety of other signalling pathways that affect vascular tone, in particular interactions with the sympathetic nervous system and the renin,angiotensin,aldosterone system. We sought to characterize the effects of intravenous IGF-I on blood pressure and on responses to noradrenaline (NA), angiotensin II, acetylcholine and dobutamine. 2Administration of IGF-I administration caused small decreases in mean arterial pressure (5.4 ± 1.5%) and responsiveness to the prazosin-sensitive vasoconstrictor effects of NA (a 2.1 ± 0.6-fold increase in ED50; n = 40; P < 0.01) and both effects were maximal at 200 µg/kg IGF-I. In addition, IGF-I significantly increased pulse pressure increases induced by low doses of dobutamine (from an increase in pulse pressure of 9.9 ± 1.2 to 13.4 ± 1.9 mmHg; n = 39; P < 0.05). Administration of IGF-I had no significant effect on responses to AngII or ACh. 3Intravenous administration of IGF-I receptor antisense oligonucleotides (400 µg/kg) abolished the effects of IGF-I on NA-induced vasoconstriction (n = 11; P < 0.05), whereas administration of a mismatch oligonucleotide did not. 4These data indicate that the maximal effects of exogenously administered IGF-I include modest direct vasodilation and inhibition of constrictor responses to NA and an increase in the effect of dobutamine on pulse pressure. The magnitude of these effects was less than what previous in vitro studies and those performed in anaesthetized animals may have indicated likely. 5The modest magnitude of the dilator effects of IGF-I observed in conscious rats in vivo in the present study suggests that IGF-I is unlikely to be a major player in regulating vascular tone in normotensive animals. [source] | ||||||||||