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1.
The Drosophila salivary glands (SGs) were well known for the puffing patterns of their polytene chromosomes and so became a tissue of choice to study sequential gene activation by the steroid hormone ecdysone. One well‐documented function of these glands is to produce a secretory glue, which is released during pupariation to fix the freshly formed puparia to the substrate. Over the past two decades SGs have been used to address specific aspects of developmentally‐regulated programmed cell death (PCD) as it was thought that they are doomed for histolysis and after pupariation are just awaiting their fate. More recently, however, we have shown that for the first 3–4 h after pupariation SGs undergo tremendous endocytosis and vacuolation followed by vacuole neutralization and membrane consolidation. Furthermore, from 8 to 10 h after puparium formation (APF) SGs display massive apocrine secretion of a diverse set of cellular proteins. Here, we show that during the period from 11 to 12 h APF, the prepupal glands are very active in calcium oxalate (CaOx) extrusion that resembles renal or nephridial excretory activity. We provide genetic evidence that Prestin, a Drosophila homologue of the mammalian electrogenic anion exchange carrier SLC26A5, is responsible for the instantaneous production of CaOx by the late prepupal SGs. Its positive regulation by the protein kinases encoded by fray and wnk lead to increased production of CaOx. The formation of CaOx appears to be dependent on the cooperation between Prestin and the vATPase complex as treatment with bafilomycin A1 or concanamycin A abolishes the production of detectable CaOx. These data demonstrate that prepupal SGs remain fully viable, physiologically active and engaged in various cellular activities at least until early pupal period, that is, until moments prior to the execution of PCD.  相似文献   
2.
Wolfgang Horn 《Hydrobiologia》1991,225(1):115-120
Planktonic crustacean biomass as well as structure are important factors influencing water transparency. The significant dependence of the water quality (Secchi depth) on the concentration and the share of the Daphnia biovolume and not on the total Crustacea biovolume in the Saidenbach reservoir indicates that the density of the Crustacea is only a measure of the cleaning performance, if Daphnia dominates. Using the mean size, the influence of the crustacean structure on the Secchi depth can be recorded. If big size categories prevail (like Daphnia) the water transparency is high. The mainly occurrence of little species (Mesocyclops, Bosmina) results in lower Secchi depths. However, a well defined (significant) relationship is being prevented by the different feeding behaviour of the several species.  相似文献   
3.
Peanuts and other seed and grain crops are commonly contaminated with carcinogenic aflatoxins, secondary metabolites produced by Aspergillus flavus and A. parasiticus. Aflatoxin contamination of peanuts in the field can be reduced by 77–98% with biological control through the application of nontoxigenic strains of these species, which competitively exclude native aflatoxin-producing strains from developing peanuts. In this study, viable peanut seeds were artificially wounded and inoculated with field soil containing natural fungal populations that were supplemented with conidia of nontoxigenic A. flavus NRRL 21882 (niaD nitrate-nonutilizing mutant) and A. parasiticus NRRL 21369 (conidial color mutant). Increasing soil densities of applied nontoxigenic strains generally resulted in an increase in the incidence of seed colonization by applied nontoxigenic strains, a decrease in seed colonization by native A. flavus and A. parasiticus, and a decrease in aflatoxin concentration in seeds. Reduction of aflatoxins in peanut seeds depended on both the density and the aflatoxin-producing potential of native populations and on the fungal strain used for biological control. Wild-type strain A. flavus NRRL 21882 and its niaD mutant were equally effective in reducing aflatoxins in peanuts, indicating that nitrate-nonutilizing mutants, which are easily monitored in the field, can be used for evaluating the efficacy of biocontrol strains.  相似文献   
4.
Acquired or intrinsic resistance to apoptotic and necroptotic stimuli is considered a major hindrance of therapeutic success in malignant melanoma. Inhibitor of apoptosis proteins (IAPs) are important regulators of apoptotic and necroptotic cell death mediated by numerous cell death signalling platforms. In this report we investigated the impact of IAPs for cell death regulation in malignant melanoma. Suppression of IAPs strongly sensitized a panel of melanoma cells to death ligand-induced cell death, which, surprisingly, was largely mediated by apoptosis, as it was completely rescued by addition of caspase inhibitors. Interestingly, the absence of necroptosis signalling correlated with a lack of receptor-interacting protein kinase-3 (RIPK3) mRNA and protein expression in all cell lines, whereas primary melanocytes and cultured nevus cells strongly expressed RIPK3. Reconstitution of RIPK3, but not a RIPK3-kinase dead mutant in a set of melanoma cell lines overcame CD95L/IAP antagonist-induced necroptosis resistance independent of autocrine tumour necrosis factor secretion. Using specific inhibitors, functional studies revealed that RIPK3-mediated mixed-lineage kinase domain-like protein (MLKL) phosphorylation and necroptosis induction critically required receptor-interacting protein kinase-1 signalling. Furthermore, the inhibitor of mutant BRAF Dabrafenib, but not Vemurafenib, inhibited necroptosis in melanoma cells whenever RIPK3 is present. Our data suggest that loss of RIPK3 in melanoma and selective inhibition of the RIPK3/MLKL axis by BRAF inhibitor Dabrafenib, but not Vemurafenib, is critical to protect from necroptosis. Strategies that allow RIPK3 expression may allow unmasking the necroptotic signalling machinery in melanoma and points to reactivation of this pathway as a treatment option for metastatic melanoma.Over the past few years, necroptosis has been established as an alternative programmed form of cell death, contrasting caspase-dependent apoptosis. It is now evident that an ordered activation of the receptor-interacting protein kinases-1 and -3 (RIPK1 and RIPK3), and their downstream substrates is mandatory for the execution of necroptosis.1, 2, 3 Under caspase-limited conditions, the necroptotic cell signalling machinery is regulated by RIPK1, with the impact of scaffolding function as compared with kinase function still unclear.1, 4, 5, 6 RIPK1 interacts with and either autophosphorylates or transphosphorylates RIPK3 (for review, see Cho et al.,1 Zhang et al.,2 He et al.,3 and Vanden Berghe et al.7). When RIPK1 is active, RIPK3 phosphorylation and activation occurs within the assembled Necrosome (for review, see Remijsen et al.8) or Ripoptosome.4, 9, 10 RIPK3 then phosphorylates the pseudo kinase mixed-lineage kinase domain-like protein (MLKL).11 MLKL in its active form allows its oligomerization, membrane accumulation, and complex formation within cellular membranes of the mitochondria12 and cell membranes,13 and finally results in necroptosis.14The RIPK1/RIPK3/MLKL signalling network acts as a sensor for genotoxic stress9 and also has a key role in necroptosis regulation in keratinocyte skin cancer (SCC).4 In these epithelial cancers, cellular inhibitors of apoptosis proteins (cIAPs) block both apoptotic and necroptotic cell death.4, 5 Both apoptosis and necroptosis can be increasingly initiated by intrinsic or extrinsic stimuli when IAPs are suppressed by IAP antagonist. Extrinsic apoptosis mediated by activation of death receptors (DRs) such as cluster of differentiation 95 (CD95), TRAILR1/R2 or tumour necrosis factor receptor-1 (TNFR1) through ligation of respective death ligands (DLs) such as CD95L, TNF-related apoptosis-inducing ligand (TRAIL), and TNF initiates apoptosis either by direct activation of the caspase cascade (caspase-8/caspase-3) or via the intrinsic cell death signalling machinery regulated by pro-apoptotic members of the Bcl-2 family followed by caspase-3 activation.15 Inhibition of caspase-8 within the death-inducing signalling complex or complex II, or within the Ripoptosome can trigger CD95L-mediated,5 TRAIL-mediated16 or TNF-induced necroptosis.8, 17 A role for apoptosis resistance, cancer maintenance, and progression is widely assumed (for review, see Obexer et al.18), but the pathophysiological inhibitory or propagating function of necroptosis has not formally been demonstrated in cancer.Metastatic melanoma has an overall poor prognosis but novel therapeutics have revolutionized clinical practice for different subsets of patients. The use of inhibitors of the V600E- or V600K-mutated proto-oncogene serine/threonine protein kinase B-RAF (e.g., Dabrafenib or Vemurafenib) results in suppression of Ras/Raf/mitogen-activated protein kinase pathways and translate into unfortunately transient clinical responses (for review, see Spagnolo et al.19). The high recrudescence of metastatic melanoma following the treatment with BRAF inhibitors will potentially require combination therapies that activate additional tumour-inhibitory pathways. Combinations such as BRAF inhibitors with mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) inhibitors have already yielded impressive results20 and other combination therapies may further improve clinical outcome.21 As BRAF inhibitors target the cell death pathway at best in an indirect manner, we reasoned that necroptosis induction could represent a novel option to improve melanoma therapy. Our investigations demonstrate for the first time that loss of RIPK3 during melanoma development is critical for necroptosis protection. Reactivation of the RIPK1/RIPK3/MLKL signalling machinery by RIPK3 reconstitution allows IAP antagonist/DL-mediated necroptosis in the presence of Vemurafenib, but not Dabrafenib. Here, Dabrafenib blocks necroptosis by interference with RIPK3-mediated MLKL phosphorylation. Therefore, strategies that increase RIPK3 expression in combination with Vemurafenib, but not Dabrafenib, likely represent an attractive strategy to overcome cell death resistance in melanoma.  相似文献   
5.
6.
The aim of this study was to identify and characterize mechanisms of resistance to antifolate drugs in African trypanosomes. Genome-wide RNAi library screens were undertaken in bloodstream form Trypanosoma brucei exposed to the antifolates methotrexate and raltitrexed. In conjunction with drug susceptibility and folate transport studies, RNAi knockdown was used to validate the functions of the putative folate transporters. The transport kinetics of folate and methotrexate were further characterized in whole cells. RNA interference target sequencing experiments identified a tandem array of genes encoding a folate transporter family, TbFT1–3, as major contributors to antifolate drug uptake. RNAi knockdown of TbFT1–3 substantially reduced folate transport into trypanosomes and reduced the parasite''s susceptibly to the classical antifolates methotrexate and raltitrexed. In contrast, knockdown of TbFT1–3 increased susceptibly to the non-classical antifolates pyrimethamine and nolatrexed. Both folate and methotrexate transport were inhibited by classical antifolates but not by non-classical antifolates or biopterin. Thus, TbFT1–3 mediates the uptake of folate and classical antifolates in trypanosomes, and TbFT1–3 loss-of-function is a mechanism of antifolate drug resistance.  相似文献   
7.
Epitheliocystis, a disease characterised by cytoplasmic bacterial inclusions (cysts) in the gill and less commonly skin epithelial cells, has been reported in many marine and freshwater fish species and may be associated with mortality. Previously, molecular and ultrastructural analyses have exclusively associated members of the Chlamydiae with such inclusions. Here we investigated a population of farmed Atlantic salmon from the west coast of Norway displaying gill epitheliocystis. Although 'Candidatus Piscichlamydia salmonis', previously reported to be present in such cysts, was detected by PCR in most of the gill samples analysed, this bacterium was found to be a rare member of the gill microbiota, and not associated with the observed cysts as demonstrated by fluorescence in situ hybridization assays. The application of a broad range 16 S rRNA targeted PCR assay instead identified a novel betaproteobacterium as an abundant member of the gill microbiota. Fluorescence in situ hybridization demonstrated that this bacterium, tentatively classified as 'Candidatus Branchiomonas cysticola', was the cyst-forming agent in these samples. While histology and ultrastructure of 'Ca. B. cysticola' cysts revealed forms similar to the reticulate and intermediate bodies described in earlier reports from salmon in seawater, no elementary bodies typical of the chlamydial developmental cycle were observed. In conclusion, this study identified a novel agent of epitheliocystis in sea-farmed Atlantic salmon and demonstrated that these cysts can be caused by bacteria phylogenetically distinct from the Chlamydiae.  相似文献   
8.
Ecosystems that are heavily invaded by an exotic species often contain abundant populations of other invasive species. This may reflect shared responses to a common factor, but may also reflect positive interactions among these exotic species. Armand Bayou (Pasadena, TX) is one such ecosystem where multiple species of invasive aquatic plants are common. We used this system to investigate whether presence of one exotic species made subsequent invasions by other exotic species more likely, less likely, or if it had no effect. We performed an experiment in which we selectively removed exotic rooted and/or floating aquatic plant species and tracked subsequent colonization and growth of native and invasive species. This allowed us to quantify how presence or absence of one plant functional group influenced the likelihood of successful invasion by members of the other functional group. We found that presence of alligatorweed (rooted plant) decreased establishment of new water hyacinth (free-floating plant) patches but increased growth of hyacinth in established patches, with an overall net positive effect on success of water hyacinth. Water hyacinth presence had no effect on establishment of alligatorweed but decreased growth of existing alligatorweed patches, with an overall net negative effect on success of alligatorweed. Moreover, observational data showed positive correlations between hyacinth and alligatorweed with hyacinth, on average, more abundant. The negative effect of hyacinth on alligatorweed growth implies competition, not strong mutual facilitation (invasional meltdown), is occurring in this system. Removal of hyacinth may increase alligatorweed invasion through release from competition. However, removal of alligatorweed may have more complex effects on hyacinth patch dynamics because there were strong opposing effects on establishment versus growth. The mix of positive and negative interactions between floating and rooted aquatic plants may influence local population dynamics of each group and thus overall invasion pressure in this watershed.  相似文献   
9.
A protein (Mr = 63,000) from calf serum that promotes the pigmentation of cultured chick neural crest and mouse melanoma cells has been partially isolated and characterized in this study. The stimulation of melanin synthesis in cultured cells was used to follow its activity during purification. The pigment-promoting factor was isolated by sequential column chromatography on dye-agarose matrices followed by hydroxyapatite and high pressure molecular sieve chromatography. The factor was found to stimulate melanin biosynthesis at 2-4 micrograms/ml and was specific for melanin-producing cells and their precursors. Antibodies raised in rabbits against the factor inhibited its pigment-promoting activity as well as that of whole calf serum. Enzyme-linked immunoadsorbent assays demonstrated that calf and bovine sera contain molecules that cross-react with the pigment-promoting factor. Horse, human, rat, and chicken sera, which lack the biological activity, also lacked immunological cross-reactivity. Extracts of certain tissues, particularly the submaxillary gland, were observed to be rich sources of pigment-promoting activity.  相似文献   
10.
When sarcolemma membranes isolated from rat skeletal muscle were incubated with [gamma-32P]ATP, a membrane protein of apparent Mr 95,000 was rapidly phosphorylated, with the 32P content reaching a maximum within 2 s. On the basis of immunoprecipitation with anti-insulin-receptor antiserum, phosphoamino acid analysis and Mr, this protein probably represents the beta-subunit of the insulin receptor. Similarly, on incubation of the membrane with adenosine 5'-[gamma-[35S]thio] triphosphate the 95 kDa protein was thiophosphorylated, indicating thiophosphorylation of the beta-subunit of the insulin receptor on the basis of immunoprecipitation studies. The effect of insulin on the phosphorylation of this protein in the membrane was studied. Insulin induced a 20% decrease in the 32P labelling of the protein when the membranes were phosphorylated for 10 s. This insulin effect was dose-dependent, with half-maximal effect obtained at 2-3 nM-insulin. Addition of GTP, but not GDP or guanosine 5'-[beta, gamma-imido]triphosphate, enhanced the effect to 35% inhibition, with half-maximal effect of GTP obtained at 0.5 microM. GTP had no effect on the phosphorylation of the protein in the absence of insulin. Analysis of this insulin effect showed that insulin increased the rate of dephosphorylation of the 95 kDa protein in the membrane. In contrast, insulin had no effect on thiophosphorylation of the 95 kDa membrane protein after incubation with adenosine 5'-[gamma-[35S]thio]triphosphate. Since thiophosphorylated proteins are less sensitive to phosphatase action, these investigations suggest that insulin stimulated a protein phosphatase activity in a GTP-dependent manner. The possibility that GTP-regulatory proteins are involved in the action of insulin on the phosphorylation of the insulin receptor and other membrane proteins is discussed.  相似文献   
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