Freezing sensitivity in the sfr4 mutant of Arabidopsis is due to low sugar content and is manifested by loss of osmotic responsiveness

Protoplasts were tested to determine whether the freezing sensitivity of the sfr4 (sensitive to freezing) mutant of Arabidopsis was due to the mutant's deficiency in soluble sugars after cold acclimation. When grown under nonacclimated conditions, sfr4 protoplasts possessed freezing tolerance similar to that of wild type, with the temperature at which 50% of protoplasts are injured (LT(50)) of -4.5 degrees C. In both wild-type and sfr4 protoplasts, expansion-induced lysis was the predominant lesion between -2 degrees C and -4 degrees C, but its incidence was low (approximately 10%); below -5 degrees C, loss of osmotic responsiveness (LOR) was the predominant lesion. After cold acclimation, the LT(50) was decreased to only -5.6 degrees C for sfr4 protoplasts, compared with -9.1 degrees C for wild-type protoplasts. Although expansion-induced lysis was precluded in both types of protoplasts, the sfr4 protoplasts remained susceptible to LOR. After incubation of seedlings in Suc solution in the dark at 2 degrees C, freezing tolerance and the incidence of freeze-induced lesions in sfr4 protoplasts were examined. The freezing tolerance of isolated protoplasts (LT(50) of -9 degrees C) and the incidence of LOR were now similar for wild type and sfr4. These results indicate that the freezing sensitivity of cold-acclimated sfr4 is due to its continued susceptibility to LOR (associated with lyotropic formation of the hexagonal II phase) and associated with the low sugar content of its cells.     

Inhibition of caspase-9 through phosphorylation at Thr 125 by ERK MAPK

Many pro-apoptotic signals activate caspase-9, an initiator protease that activates caspase-3 and downstream caspases to initiate cellular destruction. However, survival signals can impinge on this pathway and suppress apoptosis. Activation of the Ras-Raf-MEK-ERK mitogen-activated protein kinase (MAPK) pathway is associated with protection of cells from apoptosis and inhibition of caspase-3 activation, although the targets are unknown. Here, we show that the ERK MAPK pathway inhibits caspase-9 activity by direct phosphorylation. In mammalian cell extracts, cytochrome c-induced activation of caspases-9 and -3 requires okadaic-acid-sensitive protein phosphatase activity. The opposing protein kinase activity is overcome by treatment with the broad-specificity kinase inhibitor staurosporine or with inhibitors of MEK1/2. Caspase-9 is phosphorylated at Thr 125, a conserved MAPK consensus site targeted by ERK2 in vitro, in a MEK-dependent manner in cells stimulated with epidermal growth factor (EGF) or 12-O-tetradecanoylphorbol-13-acetate (TPA). Phosphorylation at Thr 125 is sufficient to block caspase-9 processing and subsequent caspase-3 activation. We suggest that phosphorylation and inhibition of caspase-9 by ERK promotes cell survival during development and tissue homeostasis. This mechanism may also contribute to tumorigenesis when the ERK MAPK pathway is constitutively activated.     

Binding Characteristics of a Potent AMPA Receptor Antagonist [3H]Ro 48-8587 in Rat Brain

Abstract: A new AMPA receptor antagonist, Ro 48-8587, was characterized pharmacologically in vitro. It is highly potent and selective for AMPA receptors as shown by its effects on [³H]AMPA, [³H]kainate, and [³H]MK-801 binding to rat brain membranes and on AMPA- or NMDA-induced depolarization in rat cortical wedges. [³H]Ro 48-8587 bound with a high affinity ( K _D = 3 n M ) to a single population of binding sites with a B _max of 1 pmol/mg of protein in rat whole brain membranes. [³H]Ro 48-8587 binding to rat whole brain membranes was inhibited by several compounds with the following rank order of potency: Ro 48-8587 > 6-nitro-7-sulphamoylbenzo[ f ]quinoxaline-2,3-dione (NBQX) > YM 90K > 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) > quisqualate > AMPA > glutamate > kainate > NMDA. The distribution and abundance of specific binding sites (∼95% of total) in sections of rat CNS, revealed by quantitative receptor radioautography and image analysis, indicated a very discrete localization. Highest binding values were observed in cortical layers (binding in layers 1 and 2 > binding in layers 3–6), hippocampal formation, striatum, dorsal septum, reticular thalamic nucleus, cerebellar molecular layer, and spinal cord dorsal horn. At 1 n M , the values for specific binding were highest in the cortical layers 1 and 2 and lowest in the brainstem (∼2.6 and 0.4 pmol/mg of protein, respectively). Ro 48-8587 is a potent and selective AMPA receptor antagonist with improved binding characteristics (higher affinity, selectivity, and specific binding) compared with those previously reported.     

Interaction of COP1 and UVR8 regulates UV‐B‐induced photomorphogenesis and stress acclimation in Arabidopsis

The ultraviolet‐B (UV‐B) portion of the solar radiation functions as an environmental signal for which plants have evolved specific and sensitive UV‐B perception systems. The UV‐B‐specific UV RESPONSE LOCUS 8 (UVR8) and the multifunctional E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) are key regulators of the UV‐B response. We show here that uvr8‐null mutants are deficient in UV‐B‐induced photomorphogenesis and hypersensitive to UV‐B stress, whereas overexpression of UVR8 results in enhanced UV‐B photomorphogenesis, acclimation and tolerance to UV‐B stress. By using sun simulators, we provide evidence at the physiological level that UV‐B acclimation mediated by the UV‐B‐specific photoregulatory pathway is indeed required for survival in sunlight. At the molecular level, we demonstrate that the wild type but not the mutant UVR8 and COP1 proteins directly interact in a UV‐B‐dependent, rapid manner in planta. These data collectively suggest that UV‐B‐specific interaction of COP1 and UVR8 in the nucleus is a very early step in signalling and responsible for the plant's coordinated response to UV‐B ensuring UV‐B acclimation and protection in the natural environment.     

RUNX3-mediated repression of RUNX1 in B cells

Are there three different RUNX genes in the human genome just to allow differential expression in different cell types or are the RUNX proteins functionally different? Much previous evidence has suggested that the RUNX proteins were functionally redundant but, in human B cells, RUNX1 and RUNX3 have clearly been shown to have different functions at a key developmental stage. RUNX1 is expressed in mature resting B cells but proliferating B cell lines express RUNX3. Repression of RUNX1 by RUNX3 is required to allow the cell proliferation and this provides an experimental system to investigate the mechanism of the different activities of RUNX1 and RUNX3 in these cells. J. Cell. Physiol. 221: 283–287, 2009. © 2009 Wiley-Liss, Inc.     

Impacts and Recovery from Severe Tropical Cyclone Yasi on the Great Barrier Reef

Full recovery of coral reefs from tropical cyclone (TC) damage can take decades, making cyclones a major driver of habitat condition where they occur regularly. Since 1985, 44 TCs generated gale force winds (≥17 metres/second) within the Great Barrier Reef Marine Park (GBRMP). Of the hurricane strength TCs (≥H1—Saffir Simpson scale; ≥ category 3 Australian scale), TC Yasi (February, 2011) was the largest. In the weeks after TC Yasi crossed the GBRMP, participating researchers, managers and rangers assessed the extent and severity of reef damage via 841 Reef Health and Impact Surveys at 70 reefs. Records were scaled into five damage levels representing increasingly widespread colony-level damage (1, 2, 3) and reef structural damage (4, 5). Average damage severity was significantly affected by direction (north vs south of the cyclone track), reef shelf position (mid-shelf vs outer-shelf) and habitat type. More outer-shelf reefs suffered structural damage than mid-shelf reefs within 150 km of the track. Structural damage spanned a greater latitudinal range for mid-shelf reefs than outer-shelf reefs (400 vs 300 km). Structural damage was patchily distributed at all distances, but more so as distance from the track increased. Damage extended much further from the track than during other recent intense cyclones that had smaller circulation sizes. Just over 15% (3,834 km²) of the total reef area of the GBRMP is estimated to have sustained some level of coral damage, with ~4% (949 km²) sustaining a degree of structural damage. TC Yasi likely caused the greatest loss of coral cover on the GBR in a 24-hour period since 1985. Severely impacted reefs have started to recover; coral cover increased an average of 4% between 2011 and 2013 at re-surveyed reefs. The in situ assessment of impacts described here is the largest in scale ever conducted on the Great Barrier Reef following a reef health disturbance.     

Inflammatory Signalling in Fetal Membranes: Increased Expression Levels of TLR 1 in the Presence of Preterm Histological Chorioamnionitis

Histological chorioamnionitis (HCA) is an established marker of ascending infection, a major cause of preterm birth. No studies have characterised the global change in expression of genes involved in the toll-like receptor (TLR) signalling pathways in the presence of HCA in the setting of preterm birth (pHCA). Fetal membranes were collected immediately after delivery and underwent histological staging for inflammation to derive 3 groups; term spontaneous labour without HCA (n = 9), preterm birth <34 weeks gestation without HCA (n = 8) and pHCA <34 weeks (n = 12). Profiling arrays ran in triplicate for each group were used to determine the expression of 84 genes associated with TLR signalling and screen for genes of interest (fold change >2; p<0.1). Expression of identified genes was validated individually for all samples, relative to GAPDH, using RT-PCR. Expression of TLR 1, TLR 2, lymphocyte antigen 96, interleukin 8 and Interleukin-1 receptor-associated kinase-like 2 was increased in pHCA (p<0.05). Degree of expression was positively associated with histological staging of both maternal and fetal inflammation (p<0.05). The inflammatory expression profile at the maternal/fetal interface associated with pHCA, a reflection of ascending infection, is extremely heterogeneous suggesting polymicrobial involvement with activation of a common pathway. Antagonism of TLR 1 and TLR 2 signalling in this setting warrants further assessment.