Notch signaling and Notch signaling modifiers

Originally discovered nearly a century ago, the Notch signaling pathway is critical for virtually all developmental programs and modulates an astounding variety of pathogenic processes. The DSL (Delta, Serrate, LAG-2 family) proteins have long been considered canonical activators of the core Notch pathway. More recently, a wide and expanding network of non-canonical extracellular factors has also been shown to modulate Notch signaling, conferring newly appreciated complexity to this evolutionarily conserved signal transduction system. Here, I review current concepts in Notch signaling, with a focus on work from the last decade elucidating novel extracellular proteins that up- or down-regulate signal potency.     

外源突变基因AGM3过表达对烟草开花的抑制和花器官发育的影响

为了解AGM3基因在异源植物中对开花及花器官发育的影响,采用农杆菌介导法将dominant negative mutation(DNM)结构基因35S-AGM3-E9导入烟草(Nicotiana tabacum),经PCR和Southern检测获得了一批阳性转化植株.荧光定量分析结果显示,AGM3在各个转基因株系中均有...     

Repeated agonistic encounters in hamsters modulate AVP V1a receptor binding

Arginine vasopressin (AVP) regulates aggression in male Syrian hamsters. In this study, we used radioligand receptor autoradiography to examine whether changes in agonistic behavior following acute and repeated social defeat are accompanied by changes in AVP V1a receptor binding. Social defeat produced high levels of submissive behavior and a loss of territorial aggression when hamsters were subsequently tested with a novel intruder, and repeated agonistic encounters produced similar behavioral changes in subordinates. AVP V1a receptor binding was not reduced by acute social defeat but was affected by repeated agonistic encounters. Dominants had significantly more AVP V1a receptor binding in lateral portions of the ventromedial hypothalamus (VMHL) than did their subordinate opponents, but subordinates were no different from controls. In contrast, receptor binding did not differ in most other brain regions examined. The changes in receptor binding appear to be independent of testosterone levels, as testosterone levels did not differ among dominants, subordinates, and controls. Our results suggest that changes in AVP V1a receptors do not account for the changes in agonistic behavior produced by acute social defeat but AVP V1a binding in the VMHL correlates with, and may modulate, the behavioral changes that occur following repeated experiences of victory.     

Rab27b localizes to zymogen granules and regulates pancreatic acinar exocytosis

To understand the function of pancreatic zymogen granules, we performed a proteomics analysis to identify ZG membrane components. Here we report the identification of Rab27b through this proteomics study and validate its role in granule function. MALDI-MS peptide mass fingerprint was matched to rat Rab27b with 43% sequence coverage, and the identification was also confirmed by tandem mass spectrometry. The localization of Rab27b on ZGs was confirmed by Western blotting and immunocytochemistry. To examine the function of Rab27b in acinar secretion, we overexpressed wild type and mutant Rab27b protein in pancreatic acini using recombinant adenoviruses. Wild type Rab27b had no effect on amylase secretion, while Rab27b Q78L enhanced, and Rab27b N133I inhibited, CCK-induced amylase release by 92+/-13% and 53+/-8%, respectively. This enhancement and inhibition occurred at all points on the CCK dose-response curve and over a 30min time course. These results demonstrate that Rab27b is present on ZGs and plays an important role in regulating acinar exocytosis.     

莴笋地蜘蛛优势种的空间生态位研究

通过对莴笋地蜘蛛优势种的空间生态位研究,发现蜘蛛优势种在每天的上午、中午和下午的空间生态宽度指数值和生态位重叠指数值大小均有较大变化,下午的蜘蛛生态位宽度指数值和生态位重叠指数值较大,上午的次之,中午的最小。     

Benthic community responses to nutrient enrichment and predator exclusion: Influence of background nutrient concentrations and interactive effects

Potential community effects of nutrient enhancement are a topic of theoretical interest and increasing management concern in coastal marine systems. While increased nutrient levels may lead to increased microalgal production and biomass, studies have provided variable evidence regarding the existence of upward cascade effects on macrofauna. In benthic marine communities, limitation by predation or factors preventing recruitment response may contribute to weak coupling between resource availability and macrobenthos abundances. We conducted blocked nutrient addition and predator exclusion experiments in the intertidal of two estuaries that varied in background nutrient concentrations (Cape Fear and White Oak, southeastern North Carolina). Benthic community comparisons were also made among these and two other North Carolina estuaries to examine correlations in distribution patterns. Cape Fear, which had the highest background nitrogen and phosphorus concentrations, also had highest ambient benthic microalgal biomass. There was no significant response of microalgal biomass to local nutrient additions in Cape Fear and only one macrofaunal taxon during one season exhibited abundance responses to nutrient additions. White Oak, with lower background nutrient levels, was characterized by significant microalgal responses to nutrient additions and significant macrofauna abundance responses for 50% of the species examined during summer experiments. However, all of these macrofauna declined in abundance with nutrient enhancement while biomass remained constant or significantly increased with nutrient additions. This suggests a complex response of macrofauna to nutrient additions in this estuary with greater biomass per individual but a corresponding decline in abundances. Top-down/bottom-up interactive effects were observed for haustoriid amphipods, which were uncommon or absent when predators had access, but exhibited strong biomass responses to nutrient enhancement when predators were excluded. These results support a growing body of literature that indicates the importance of background conditions in regulating benthic community responses to nutrient enhancement. However, responses may be complex with biomass per individual rather than densities being the primary response variable for some taxa and predator moderation of responses occurring for some taxa but not others.     

Dominant negative effects of a Gbeta mutant on G-protein coupled inward rectifier K+ channel

HEK293 cells were transfected with cDNAs for Gbeta1(W332A) [a mutant Gbeta1], Ggamma2, and inward rectifier K+ channels (Kir3.1/Kir3.2). Application of Gbeta1gamma2 protein to these cells activated the K+ channels only slightly. When mu-opioid receptors and Kir3.1/Kir3.2 were transfected, application of a mu-opioid agonist induced a Kir3 current. However, co-expression of Gbeta1(W332A) suppressed this current. Most likely, Gbeta1(W332A) inhibited the action of the endogenous Gbeta. Such a dominant negative effect of Gbeta1(W332A) was also observed in neuronal Kir3 channels in locus coeruleus. The mutant, Gbeta1(W332A) protein, although inactive, retains its ability to bind Kir3 and prevents the wild type Gbeta from activating the channel.     

A Dominant Negative Heterozygous G87R Mutation in the Zinc Transporter, ZnT-2 (SLC30A2), Results in Transient Neonatal Zinc Deficiency

Zinc is an essential mineral, and infants are particularly vulnerable to zinc deficiency as they require large amounts of zinc for their normal growth and development. We have recently described the first loss-of-function mutation (H54R) in the zinc transporter ZnT-2 (SLC30A2) in mothers with infants harboring transient neonatal zinc deficiency (TNZD). Here we identified and characterized a novel heterozygous G87R ZnT-2 mutation in two unrelated Ashkenazi Jewish mothers with infants displaying TNZD. Transient transfection of G87R ZnT-2 resulted in endoplasmic reticulum-Golgi retention, whereas the WT transporter properly localized to intracellular secretory vesicles in HC11 and MCF-7 cells. Consequently, G87R ZnT-2 showed decreased stability compared with WT ZnT-2 as revealed by Western blot analysis. Three-dimensional homology modeling based on the crystal structure of YiiP, a close zinc transporter homologue from Escherichia coli, revealed that the basic arginine residue of the mutant G87R points toward the membrane lipid core, suggesting misfolding and possible loss-of-function. Indeed, functional assays including vesicular zinc accumulation, zinc secretion, and cytoplasmic zinc pool assessment revealed markedly impaired zinc transport in G87R ZnT-2 transfectants. Moreover, co-transfection experiments with both mutant and WT transporters revealed a dominant negative effect of G87R ZnT-2 over the WT ZnT-2; this was associated with mislocalization, decreased stability, and loss of zinc transport activity of the WT ZnT-2 due to homodimerization observed upon immunoprecipitation experiments. These findings establish that inactivating ZnT-2 mutations are an underlying basis of TNZD and provide the first evidence for the dominant inheritance of heterozygous ZnT-2 mutations via negative dominance due to homodimer formation.