Employing optical lightning data to identify lightning flashes associated to terrestrial gamma-ray flashes.

Terrestrial gamma-ray flashes (TGFs) are bursts of energetic X- and gamma-rays emitted from thunderstorms. The Atmosphere-Space Interactions Monitor (ASIM) mounted onto the International Space Station (ISS) is dedicated to measure TGFs and optical signatures of lightning; ISS LIS (Lightning Imaging Sensor) detects lightning flashes allowing for simultaneous measurements with ASIM. Whilst ASIM measures ∼300-400 TGFs per year, ISS LIS detects ∼106 annual lightning flashes giving a disproportion of four orders of magnitude. Based on the temporal evolution of lightning flashes and the spatial pattern of the constituing events, we present an algorithm to reduce the number of space-detected flashes potentially associated with TGFs by ∼ 60% and of associated LIS groups by ∼ 95%. We use ASIM measurements to confirm that the resulting flashes are indeed those associated with TGFs detected at approx. 400 km altitude and thus benchmark our algorithm preserving 70-80% of TGFs from concurrent ASIM-LIS measurements. We compare how the radiance, footprint size and the global distribution of lightning flashes of the reduced set relates to the average of all measured lightning flashes and do not observe any significant difference. Finally, we present a parameter study of our algorithm and discuss which parameters can be tweaked to maximize the reduction efficiency whilst keeping flashes associated to TGFs. In the future, this algorithm will hence be capable of facilitating the search for TGFs in a reduced set of lightning flashes measured from space.

Sublytic terminal complement attack on myotubes decreases the expression of mRNAs encoding muscle-specific proteins.

Activation of inflammatory and cytotoxic complement effectors that include the C5b-9 complex plays an important pathogenic role in myasthenia gravis, an inflammatory autoimmune disease of the muscle. Altered muscle-specific gene expression has been observed in experimental myasthenic rats. In this study, we have examined the effect of sublytic C5b-9 on myotubes differentiated from C2C12 myoblasts, by generating C5b-9 with C7-deficient serum with or without C7. Within 2 h, C7-deficient serum plus C7, compared with C7-deficient serum alone, induced markedly decreased levels of mRNAs encoding alpha-actin, troponin I slow twitch isoform, acetylcholine receptor alpha, and muscle aldolase A, whereas the heat shock protein 83 mRNA level remained constant, by northern analysis. Because the half-life of the acetylcholine receptor alpha was estimated to be > 8 h, the C5b-9 effect was, in part, due to enhanced mRNA decay. Because C5b-9 also induced c-jun mRNA and reduced the myoD mRNA level, a possible inhibition of muscle gene transcription by C5b-9 was examined in myotubes transfected with troponin promoter-luciferase gene constructs. Luciferase activity was reduced to 50% in response to C5b-9 at 2 h. Thus, C5b-9 appears to inhibit the muscle-specific gene expression by stimulating mRNA decay and by decreasing the transcription process. The data also indicate a possible pathogenic role of C5b-9 in immune-mediated inflammatory muscle disorders in which complement activation has been implicated.

Activation of the alternative complement pathway and production of factor H by skeletal myotubes.

Skeletal muscle myotubes from neonatal rats were used to study the interaction of skeletal muscle with complement. Serum from guinea pig, rabbit, and human, in the absence of muscle-specific antibody, caused creatine phosphokinase release, which required activation of the terminal complement cascade. Cleavage of serum C3 and Factor B in the presence of myotubes was dependent on Mg2+, but not Ca2+, and C3 cleavage occurred only in the presence of Factor B. Rat myotubes caused significant consumption of C8 and C9 in rat serum, which also required Mg2+, but not Ca2+. All of these findings are typical of a tissue capable of activating the alternative pathway. In addition, the C2 myotube cell line was shown to produce Factor H, an inhibitory protein of the alternative pathway, as demonstrated by Factor H mRNA expression and immunoprecipitation of the protein.

Multiple signal messengers generated by terminal complement complexes and their role in terminal complement complex elimination.

The best established function of C5b-9 is the ability to lyse or kill cells after assembly in the plasma membrane. In addition to this cytolytic function, increasing evidence suggests that C5b-9 also stimulate a variety of cell functions in vitro. Relatively little is known about the C5b-9 signals responsible for cell activation other than a transient increase in cytosolic Ca2+ primarily due to Ca2+ influx that have been determined in a cell population. In this report, signal messenger generation in Ehrlich cells by the sublytic terminal complement complexes (TCC), C5b-9, C5b-8, and C5b-7, was further examined, as well as the role of signal messengers in stimulating elimination of TCC from the cell surface. Changes in cytosolic Ca2+ were monitored in individual cells after a single dose of C5b-9 by digital imaging fluorescence microscopy that revealed oscillations in cytosolic Ca2+ over a period of 10 min. Sublytic C5b-9 substantially increased protein kinase C (PKC) activity at an external Ca2+ concentration of 1.5 mM. C5b-9-mediated PKC activation could be inhibited by 60 to 80% when external Ca2+ was reduced to 0.015 mM. C5b-8, but not C5b-7, activated PKC to a lesser extent. C5b-8 and C5b-7 also stimulated an increase in cAMP. Rapid elimination of TCC known to be stimulated by Ca2+ signal was partially inhibited by protein kinase inhibitors, H-7 and to a lesser extent by HA1004, suggesting a role for PKC in the elimination response. TCC elimination was not accelerated by agents that increase cAMP.

Developmental and protein modification defects caused by mutations in the Drosophila gene l(3)c21R.

A temperature-sensitive Drosophila mutation, l(3)c21RRW630 (abbreviated RW630), has been previously shown to have biochemical as well as developmental defects. To analyze further the relationship between the biochemical and developmental defects, recombinational mapping, deletion analysis, and complementation studies with other l(3)c21R alleles were performed. These experiments showed that the biochemical and developmental defects in RW630 can be attributed to a single mutation. Four non-temperature-sensitive l(3)c21R alleles were found to have biochemical defects similar to those seen in RW630 at restrictive temperature. In RW630 and in these four other l(3)c21R alleles, the severity of expression of the biochemical and the developmental defects was closely correlated. Temperature-shift studies of the expression of the RW630 maternal lethal effect on embryogenesis in females transheterozygous for RW630 and other l(3)c21R alleles yielded results which indicated that these defects must accumulate over a period of time before the maternal lethal effect can be detected. These data provide further support for the hypothesis that defects in protein modification produce developmental defects in l(3)c21R mutants.

Defects in protein modification precede developmental defects in l(3)c21RRW630, a temperature-sensitive Drosophila developmental mutant.

The temperature-sensitive Drosophila developmental mutation, l(3)c21RRW630 (abbreviated RW630) disturbs oogenesis and has a maternal effect on embryogenesis. At restrictive temperature, RW630 alters post-translational modification of three abundant proteins. To examine the causal relationship between these biochemical defects and the developmental defects in RW630, a series of temperature-shift experiments was performed. It was found that defects in protein modification could be detected in RW630 ovaries after RW630 females had been exposed to restrictive temperature for 1 day. RW630 females treated in this fashion produce embryos which contain a low level of unmodified proteins. Nevertheless, these embryos hatch at a normal rate. Since these ovaries and these embryos are developmentally normal, but do show defects in protein modification, it is unlikely that the RW630 developmental defects cause the biochemical defects in RW630. It is more likely that accumulation of unmodified proteins after extended exposure to restrictive temperature produces the developmental defects in RW630.

Specific protein modifications are altered in a temperature-sensitive Drosophila developmental mutant.

The temperature-sensitive Drosophila mutation l(3)c21RRW630 disturbs oogenesis and imaginal disc development and has a maternal effect on embryogenesis. Two-dimensional gel electrophoretic analysis of protein synthesis in mutant tissue at a restrictive temperature shows that the synthesis of three proteins is elevated and the synthesis of three other proteins is reduced, when compared to wild type. Each protein with increased synthesis is similar to a protein whose synthesis is reduced, as judged by comparison of partial proteolytic digests of these proteins. To explain these findings, we propose that the wild-type c21R gene codes for a protein-modifying enzyme. This enzyme catalyzes the acidic modification of three abundant proteins. The correct modification of these proteins is required for cell division, cell motility, and the formation of adult hairs and bristles. In the mutant at restrictive temperature, the enzyme does not function properly and so the unmodified substrate proteins accumulate. This study correlates the morphological defects in a Drosophila developmental mutant with an altered molecular process.

Quantitative variability in requirements for opsonization of strains within the Bacteroides fragilis group.

Requirements for opsonization of various strains within the species Bacteroides fragilis, Bacteroides thetaiotaomicron, Bacteroides vulgatus, and Bacteroides distasonis were investigated. The minimal concentration of normal human serum that facilitated maximal uptake by human peripheral leukocytes of 14C-labeled strains ranged from 5% to 80%. Heated (56 C at 30 min) serum produced less uptake than untreated serum, suggesting that complement was required for opsonization. Using human serum depleted of C4 by immunoadsorption as the source of opsonins, predominant utilization of the alternative complement pathway during opsonization was established. Acidic polyanionic exopolymer on the strains was also assessed by ruthenium red staining, electron microscopy, and India ink wet mounts. Strains of the species B thetaiotaomicron, B vulgatus, and B fragilis possessed exopolymer, and a unique configuration of this material was observed on two strains that resisted opsonization. Utilization of classical and/or alternative complement pathway activity during opsonization was not related to the presence of exopolymer.