γCOP Is Required for Apical Protein Secretion and Epithelial Morphogenesis in Drosophila melanogaster

Background: There is increasing evidence that tissue-specific modifications of basic cellular functions play an important role in development and disease. To identify the functions of COPI coatomer-mediated membrane trafficking in Drosophila development, we were aiming to create loss-of-function mutations in the γCOP gene, which encodes a subunit of the COPI coatomer complex. Principal Findings: We found that γCOP is essential for the viability of the Drosophila embryo. In the absence of zygotic γCOP activity, embryos die late in embryogenesis and display pronounced defects in morphogenesis of the embryonic epidermis and of tracheal tubes. The coordinated cell rearrangements and cell shape changes during tracheal tube morphogenesis critically depend on apical secretion of certain proteins. Investigation of tracheal morphogenesis in γCOP loss-of-function mutants revealed that several key proteins required for tracheal morphogenesis are not properly secreted into the apical lumen. As a consequence, γCOP mutants show defects in cell rearrangements during branch elongation, in tube dilation, as well as in tube fusion. We present genetic evidence that a specific subset of the tracheal defects in γCOP mutants is due to the reduced secretion of the Zona Pellucida protein Piopio. Thus, we identified a critical target protein of COPI-dependent secretion in epithelial tube morphogenesis. Conclusions/Significance: These studies highlight the role of COPI coatomer-mediated vesicle trafficking in both general and tissue-specific secretion in a multicellular organism. Although COPI coatomer is generally required for protein secretion, we show that the phenotypic effect of γCOP mutations is surprisingly specific. Importantly, we attribute a distinct aspect of the γCOP phenotype to the effect on a specific key target protein

Exogenous quinones inhibit photosynthetic electron transfer in Chloroflexus aurantiacus by specific quenching of the excited bacteriochlorophyll c antenna

AbstractIn the photosynthetic green filamentous bacterium Chloroflexus aurantiacus, excitation energy is transferred from a large bacteriochlorophyll (BChl) c antenna via smaller BChl a antennas to the reaction center. The effects of substituted 1,4-naphthoquinones on BChl c and BChl a fluorescence and on flash-induced cytochrome c oxidation were studied in whole cells under aerobic conditions. BChl c fluorescence in a cell suspension with 5.4 μM BChl c was quenched to 50% by addition of 0.6 μM shikonin ((R)-2-(1-hydroxy-4-methyl-3-pentenyl)-5,8-dihydroxy-1,4-naphthoquinone), 0.9 μM 5-hydroxy-1,4-naphthoquinone, or 4 μM 2-acetyl-3-methyl-1,4-naphthoquinone. Between 25 and 100 times higher quinone concentrations were needed to quench BChl a fluorescence to a similar extent. These quinones also efficiently inhibited flash-induced cytochrome c oxidation when BChl c was excited, but not when BChl a was excited. The quenching of BChl c fluorescence induced by these quinones correlated with the inhibition of flash-induced cytochrome c oxidation. We concluded that the quinones inhibited electron transfer in the reaction center by specifically quenching the excitation energy in the BChl c antenna. Our results provide a model system for studying the redox-dependent antenna quenching in green sulfur bacteria because the antennas in these bacteria inherently exhibit a sensitivity to O2 similar to the quinone-supplemented cells of Cfx. aurantiacus

Measurement of the lifetime of the first 2+^{\bf +} state in 124^{124}Ba

The lifetime of the first 2$^{+}$ state in the nucleus $^{124}$Ba has been measured by $\gamma$-$\gamma$ coincidence recoil-distance Doppler shift method. The $^{109}$Ag($^{19}$F, 4$n$)$^{124}$Ba reaction at a beam energy of 75 MeV was employed to populate excited states in $^{124}$Ba. The mean lifetime was determined to be 275(12) ps using the differential decay curve method. The value of $B({\rm E}2;0_{1}^{+}\rightarrow 2_{1}^{+})$ for $^{124}$Ba deduced from the lifetime is in reasonable agreement with the prediction of the proton-neutron interacting boson model(IBM-2) without Pauli blocking effect