The gelation kinetics of platelet extracts

The kinetics of the gelation process that occurs upon warming cold platelet extracts were studied using a sensitive rheometer. At micromolar or less free Ca²⁺ concentrations and in the presence of 1 mM ATP, the gel rigidity curves showed several peaks, indicating that platelet extract proteins went through network assembling/disassembling cycles during gelation. The gelation kinetics were accelerated by increasing the free Ca²⁺ concentration up to about 2 μM. At 4–15 μM free Ca²⁺, the gelation cycles were completely abolished except for the first peak. The gelation process became one of monotonically increasing elastic modulus at millimolar free Ca²⁺ concentrations. Trifluoperazine (50 μM), a calmodulin inhibitor, did not affect gelation at micromolar free Ca²⁺ concentrations. Except for the first gelation step, which was completed within 5 min after warming, the rest of the gelation process was found to be affected by K⁺, ATP, cytochalasin E and colchicine. K⁺ at concentrations higher than 10 mM retarded the gelation kinetics. Extracts prepared with low (0.1 mM) ATP content showed impaired gelations, and this was partially reversed by adding 1 mM ATP, but not 1 mM adenylylimidodiphosphate (p[NH]ppA). Both cytochalasin E (1 μM) and colchicine (1 mM) interfered with the gelation process.     

Inflammasomes in infection and inflammation

Two of the main challenges that multicellular organisms faced during evolution were to cope with invading microorganisms and eliminate and replace dying cells. Our innate immune system evolved to handle both tasks. Key aspects of innate immunity are the detection of invaders or tissue injury and the activation of inflammation that alarms the system through the action of cytokine and chemokine cascades. While inflammation is essential for host resistance to infections, it is detrimental when produced chronically or in excess and is linked to various diseases, most notably auto-immune diseases, auto-inflammatory disorders, cancer and septic shock. Essential regulators of inflammation are enzymes termed “the inflammatory caspases”. They are activated by cellular sensors of danger signals, the inflammasomes, and subsequently convert pro-inflammatory cytokines into their mature active forms. In addition, they regulate non-conventional protein secretion of alarmins and cytokines, glycolysis and lipid biogenesis, and the execution of an inflammatory form of cell death termed “pyroptosis”. By acting as key regulators of inflammation, energy metabolism and cell death, inflammatory caspases and inflammasomes exert profound influences on innate immunity and infectious and non-infectious inflammatory diseases. Christian R. McIntire and Garabet Yeretssian have contributed equally to this review.     

The role of HLA-G in human pregnancy

Pregnancy in mammals featuring hemochorial placentation introduces a major conflict with the mother's immune system, which is dedicated to repelling invaders bearing foreign DNA and RNA. Numerous and highly sophisticated strategies for preventing mothers from rejecting their genetically different fetus(es) have now been identified. These involve production of novel soluble and membrane-bound molecules by uterine and placental cells. In humans, the placenta-derived molecules include glycoproteins derived from the HLA class Ib gene, HLA-G. Isoforms of HLA-G saturate the maternal-fetal interface and circulate in mothers throughout pregnancy. Uteroplacental immune privilege for the fetus and its associated tissues is believed to result when immune cells encounter HLA-G. Unequivocally demonstration of this concept requires experiments in animal models. Both the monkey and the baboon express molecules that are similar but not identical to HLA-G, and may comprise suitable animal models for establishing a central role for these proteins in pregnancy.     

A novel zf-MYND protein, CHB-3, mediates guanylyl cyclase localization to sensory cilia and controls body size of Caenorhabditis elegans

Cilia are important sensory organelles, which are thought to be essential regulators of numerous signaling pathways. In Caenorhabditis elegans, defects in sensory cilium formation result in a small-body phenotype, suggesting the role of sensory cilia in body size determination. Previous analyses suggest that lack of normal cilia causes the small-body phenotype through the activation of a signaling pathway which consists of the EGL-4 cGMP-dependent protein kinase and the GCY-12 receptor-type guanylyl cyclase. By genetic suppressor screening of the small-body phenotype of a cilium defective mutant, we identified a chb-3 gene. Genetic analyses placed chb-3 in the same pathway as egl-4 and gcy-12 and upstream of egl-4. chb-3 encodes a novel protein, with a zf-MYND motif and ankyrin repeats, that is highly conserved from worm to human. In chb-3 mutants, GCY-12 guanylyl cyclase visualized by tagged GFP (GCY-12::GFP) fails to localize to sensory cilia properly and accumulates in cell bodies. Our analyses suggest that decreased GCY-12 levels in the cilia of chb-3 mutants may cause the suppression of the small-body phenotype of a cilium defective mutant. By observing the transport of GCY-12::GFP particles along the dendrites to the cilia in sensory neurons, we found that the velocities and the frequencies of the particle movement are decreased in chb-3 mutant animals. How membrane proteins are trafficked to cilia has been the focus of extensive studies in vertebrates and invertebrates, although only a few of the relevant proteins have been identified. Our study defines a new regulator, CHB-3, in the trafficking process and also shows the importance of ciliary targeting of the signaling molecule, GCY-12, in sensory-dependent body size regulation in C. elegans. Given that CHB-3 is highly conserved in mammal, a similar system may be used in the trafficking of signaling proteins to the cilia of other species.     

Turning Down the Heat: Vegetation Feedbacks Limit Fire Regime Responses to Global Warming

Ecosystems - Climate change is projected to dramatically increase boreal wildfire activity, with broad ecological and socioeconomic consequences. As global temperatures rise, periods with elevated...     

Mechanochemical coupling of formin-induced actin interaction at the level of single molecular complex

Biomechanics and Modeling in Mechanobiology - Formins promote actin assembly and are involved in force-dependent cytoskeletal remodeling. However, how force alters the formin functions still needs...     

Loss of Catalytically Inactive Lipid Phosphatase Myotubularin-related Protein 12 Impairs Myotubularin Stability and Promotes Centronuclear Myopathy in Zebrafish

X-linked myotubular myopathy (XLMTM) is a congenital disorder caused by mutations of the myotubularin gene, MTM1. Myotubularin belongs to a large family of conserved lipid phosphatases that include both catalytically active and inactive myotubularin-related proteins (i.e., “MTMRs”). Biochemically, catalytically inactive MTMRs have been shown to form heteroligomers with active members within the myotubularin family through protein-protein interactions. However, the pathophysiological significance of catalytically inactive MTMRs remains unknown in muscle. By in vitro as well as in vivo studies, we have identified that catalytically inactive myotubularin-related protein 12 (MTMR12) binds to myotubularin in skeletal muscle. Knockdown of the mtmr12 gene in zebrafish resulted in skeletal muscle defects and impaired motor function. Analysis of mtmr12 morphant fish showed pathological changes with central nucleation, disorganized Triads, myofiber hypotrophy and whorled membrane structures similar to those seen in X-linked myotubular myopathy. Biochemical studies showed that deficiency of MTMR12 results in reduced levels of myotubularin protein in zebrafish and mammalian C2C12 cells. Loss of myotubularin also resulted in reduction of MTMR12 protein in C2C12 cells, mice and humans. Moreover, XLMTM mutations within the myotubularin interaction domain disrupted binding to MTMR12 in cell culture. Analysis of human XLMTM patient myotubes showed that mutations that disrupt the interaction between myotubularin and MTMR12 proteins result in reduction of both myotubularin and MTMR12. These studies strongly support the concept that interactions between myotubularin and MTMR12 are required for the stability of their functional protein complex in normal skeletal muscles. This work highlights an important physiological function of catalytically inactive phosphatases in the pathophysiology of myotubular myopathy and suggests a novel therapeutic approach through identification of drugs that could stabilize the myotubularin-MTMR12 complex and hence ameliorate this disorder.     

Predicting the points of interaction of small molecules in the NF-κB pathway

Background  

The similarity property principle has been used extensively in drug discovery to identify small compounds that interact with specific drug targets. Here we show it can be applied to identify the interactions of small molecules within the NF-κB signalling pathway.     

Masting in whitebark pine (Pinus albicaulis) depletes stored nutrients

? In masting trees, synchronized, heavy reproductive events are thought to deplete stored resources and to impose a replenishment period before subsequent masting. However, direct evidence of resource depletion in wild, masting trees is very rare. Here, we examined the timing and magnitude (local vs individual-level) of stored nutrient depletion after a heavy mast event in Pinus albicaulis. ? In 2005, the mast year, we compared seasonal changes in leaf and sapwood nitrogen (N) and phosphorus (P) concentrations and leaf photosynthetic rates in cone-bearing branches, branches that never produced cones, and branches with experimentally removed cones. We also compared nutrient concentrations in cone branches and branches that had never had cones between 2005 and 2006, and measured tree ring width and new shoot growth during 2005. ? During the mast year, N or P depletion occurred only in tissue fractions of reproductive branches, where photosynthetic rates were reduced. However, by the end of the following year, nutrients were depleted in all branches, indicating individual-level resource depletion. New shoot and radial growth were not affected by masting. ? We provide direct evidence that mast events in wild trees deplete stored nutrients. Our results highlight the importance of evaluating reproductive costs over time and at the individual level.