Genetic Models of Apoptosis-Induced Proliferation Decipher Activation of JNK and Identify a Requirement of EGFR Signaling for Tissue Regenerative Responses in Drosophila

Recent work in several model organisms has revealed that apoptotic cells are able to stimulate neighboring surviving cells to undergo additional proliferation, a phenomenon termed apoptosis-induced proliferation. This process depends critically on apoptotic caspases such as Dronc, the Caspase-9 ortholog in Drosophila, and may have important implications for tumorigenesis. While it is known that Dronc can induce the activity of Jun N-terminal kinase (JNK) for apoptosis-induced proliferation, the mechanistic details of this activation are largely unknown. It is also controversial if JNK activity occurs in dying or in surviving cells. Signaling molecules of the Wnt and BMP families have been implicated in apoptosis-induced proliferation, but it is unclear if they are the only ones. To address these questions, we have developed an efficient assay for screening and identification of genes that regulate or mediate apoptosis-induced proliferation. We have identified a subset of genes acting upstream of JNK activity including Rho1. We also demonstrate that JNK activation occurs both in apoptotic cells as well as in neighboring surviving cells. In a genetic screen, we identified signaling by the EGFR pathway as important for apoptosis-induced proliferation acting downstream of JNK signaling. These data underscore the importance of genetic screening and promise an improved understanding of the mechanisms of apoptosis-induced proliferation.     

GABAA Receptors Containing ρ1 Subunits Contribute to In Vivo Effects of Ethanol in Mice

GABA_A receptors consisting of ρ1, ρ2, or ρ3 subunits in homo- or hetero-pentamers have been studied mainly in retina but are detected in many brain regions. Receptors formed from ρ1 are inhibited by low ethanol concentrations, and family-based association analyses have linked ρ subunit genes with alcohol dependence. We determined if genetic deletion of ρ1 in mice altered in vivo ethanol effects. Null mutant male mice showed reduced ethanol consumption and preference in a two-bottle choice test with no differences in preference for saccharin or quinine. Null mutant mice of both sexes demonstrated longer duration of ethanol-induced loss of righting reflex (LORR), and males were more sensitive to ethanol-induced motor sedation. In contrast, ρ1 null mice showed faster recovery from acute motor incoordination produced by ethanol. Null mutant females were less sensitive to ethanol-induced development of conditioned taste aversion. Measurement of mRNA levels in cerebellum showed that deletion of ρ1 did not change expression of ρ2, α2, or α6 GABA_A receptor subunits. (S)-4-amino-cyclopent-1-enyl butylphosphinic acid (“ρ1” antagonist), when administered to wild type mice, mimicked the changes that ethanol induced in ρ1 null mice (LORR and rotarod tests), but the ρ1 antagonist did not produce these effects in ρ1 null mice. In contrast, (R)-4-amino-cyclopent-1-enyl butylphosphinic acid (“ρ2” antagonist) did not change ethanol actions in wild type but produced effects in mice lacking ρ1 that were opposite of the effects of deleting (or inhibiting) ρ1. These results suggest that ρ1 has a predominant role in two in vivo effects of ethanol, and a role for ρ2 may be revealed when ρ1 is deleted. We also found that ethanol produces similar inhibition of function of recombinant ρ1 and ρ2 receptors. These data indicate that ethanol action on GABA_A receptors containing ρ1/ρ2 subunits may be important for specific effects of ethanol in vivo.     

Tetraether-linked membrane monolayers in <Emphasis Type="Italic">Ferroplasma</Emphasis> spp: a key to survival in acid

Ferroplasma acidarmanus thrives in hot, extremely low pH, metal-rich solutions associated with dissolving metal sulfide ore deposits. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and thin layer chromatography analyses of F. acidarmanus membranes indicate that tetraether lipids predominate, with at least three core lipid structures. NMR measurements indicate that the cytoplasmic pH of F. acidarmanus is ~5.6. The optimal growth pH is ~1.2, and the lowest growth pH is ~0.0. Thus, these organisms maintain pH gradients across their membranes that approach 5 pH units. Tetraether lipids were originally thought to be specifically associated with thermophiles but are now known to be widely distributed within the archaeal domain. Our data, in combination with recently published results for thermophilic and mesothermophilic acidophilic archaea, indicate that there may be a stronger association between tetraether lipids and tolerance to acid and/or large metal ion gradients.     

Solid‐state NMR reveals differences in the packing arrangements of peptide aggregates derived from the aortic amyloid polypeptide medin

Several polypeptides aggregate into insoluble amyloid fibrils associated with pathologies such as Alzheimer's disease, Parkinson's disease and type 2 diabetes. Understanding the structural and sequential motifs that drive fibrillisation may assist in the discovery and refinement of effective therapies. Here we investigate the effects of three predicted amyloidogenic regions on the structure of aggregates formed by medin, a poorly characterised polypeptide associated with aortic medial amyloidosis. Solid‐state NMR is used to compare the dynamics and sheet packing arrangement of the C‐terminal region encompassing residues F⁴³GSV within full‐length medin (Med_1‐50) and two shorter peptide fragments, Med_30‐50 and Med_42‐49, lacking specific sequences predicted to be amyloidogenic._. Results show that all three peptides have different aggregate morphologies, and Med_30‐50 and Med_1‐50 have different sheet packing arrangements and dynamics to Med_42‐49. These results imply that at least two of the three predicted amyloidogenic regions are required for the formation and elongation of medin fibres observed in the disease state. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Glycan Antagonists and Inhibitors: A Fount for Drug Discovery

ABSTRACT

Glycans, the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids, represent a relatively unexploited area for drug development compared with other macromolecules. This review describes the major classes of glycans synthesized by animal cells, their mode of assembly, and available inhibitors for blocking their biosynthesis and function. Many of these agents have proven useful for studying the biological activities of glycans in isolated cells, during embryological development, and in physiology. Some are being used to develop drugs for treating metabolic disorders, cancer, and infection, suggesting that glycans are excellent targets for future drug development.     

Predicting the timing and duration of sleep in an operational setting using social factors

In recent years, there has been increasing interest in the use of bio-mathematical models to predict alertness, performance, and/or fatigue in operational settings. Current models use only biological factors to make their estimations, which can be limited in operational settings where social and geo-physical factors also dictate when sleep occurs. The interaction between social and biological factors that help determine the timing and duration of sleep during layover periods have been investigated in order to create and initially validate a mathematical model that may better predict sleep in the field. Participants were 32 male transmeridian airline pilots (17 captains, 10 first officers, and 5 second officers) flying the Sydney-Bangkok-London-Singapore-Sydney (SYD-LHR) pattern. Participants continued their regular schedule while wearing activity monitors and completing sleep and work diaries. The theoretical sleep timing model underpinning this analysis consists of separate formulations for short (<32 h) and long (>32 h) break periods. Longer break periods are split into three distinct phases-recovery (break start until first local night), personal (first local night until last local night), and preparation phases (last local night until break end)-in order to exploit potential differences specific to each. Furthermore, an iterative procedure combining prediction and retrodiction (i.e., using future duty timing information to predict current sleep timing) was developed to optimize predictive ability. Analysis found an interaction between the social and circadian sleep pressures that changed over the break period. Correlation analysis indicated a strong relationship between the actual sleep and new model's predictions (r = 0.7-0.9), a significant improvement when compared to existing models (r = 0.1-0.4). Social and circadian pressures play important roles in regulating sleep for international flight crews. An initial model has been developed in order to regulate sleep in these crews. The initial results have shown promise when applied to small sets of data; however, more rigorous validation must be carried out.     

Colour and Escape Behaviour in Polymorphic Populations of an Aposematic Poison Frog

The phenomenon of aposematism, or the pairing of antipredator defence with conspicuous or distinctive signals, serves as an excellent example of how traits act in concert to shape fitness. Not only does this complex phenotype require the integration of multiple traits, it alters the fitness pay‐offs of yet others. The protection offered by aposematism may, for example, reduce the costs associated with foraging or sexual display. Thus, well‐protected aposematic lineages should be bolder, more active and less likely to respond to perceived threats of predation than more cryptic lineages. Comparisons of differently coloured morphs of the polytypic strawberry poison frog (Oophaga pumilio) have supported the predicted behavioural correlates of aposematism, with the exception of those regarding responsiveness to simulated predators. We tested the key prediction that aposematic coloration will be associated with reduced sensitivity to predators in two polymorphic O. pumilio populations. The novel approach of studying polymorphic populations allowed us to assess the effect of colour in the absence of potentially confounding habitat differences. We found that colour was associated with the probability that a frog would attempt escape and the distance at which it fled, but only in one population, and not in the predicted direction. An overall comparison of the two populations superficially supported our predictions, but this pattern actually arose because frogs occupying higher perches were less likely to respond, a pattern that may reflect the value of high perches and the costs associated with returning to them after attempted escape. These results highlight the complexity of the relationship between predators and prey, the challenges associated with understanding how and why traits are correlated, and the intimate ties between behaviour and morphological evolution.     

A presenilin-independent aspartyl protease prefers the gamma-42 site cleavage

beta-Amyloid peptides (Abeta40 and Abeta42) are the major constituents of amyloid plaques, which are one of the hallmarks of Alzheimer's disease (AD). The Abeta is derived from sequential cleavages of amyloid precursor protein (APP) by beta- and gamma-secretases. gamma-Secretase consists of at least four proteins where presenilins (PS1 and PS2 or PS) are the catalytic subunit involved in the gamma-site cleavage of APP. Secretion of both Abeta40 and Abeta42 is significantly reduced in PS1 knock-out cells and completely abolished in cells deficient for both PS1 and PS2. Consequently, both the PS proteins play essential roles in the production of the secretory of Abeta from cells. Recent studies in primary neurons, however, suggest that PSs are not required for intracellular Abeta42 accumulation; thus the intracellular Abeta42 appears to be generated in a PS-independent manner. Here we present the first biochemical evidence indicating that Abeta, especially Abeta42, can be generated in the absence of PS based on an in vitrogamma-secretase assay employing membranes prepared from PS-deficient Blastocyst-derived (BD) cells. This PS-independent gamma-secretase (PSIG) activity is sensitive to the changes in pH and displays an optimal activity at pH 6.0. Pepstatin A is a potent inhibitor for this proteolytic activity with IC50 of 1.2 nm and 0.4 nm for Abeta40 and Abeta42 generation, respectively. These results indicate that these PS-independent gamma-site cleavages are mediated by an aspartyl protease. More importantly, the PSIG activity displays a distinct preference in mediating the 42-site cleavage over the 40-site cleavage, thereby generating Abeta42 as the predominant product.