1,473 research outputs found
Mitonuclear Interactions Produce Diverging Responses to Mild Stress in Drosophila Larvae
Mitochondrial function depends on direct interactions between respiratory proteins encoded by genes in two genomes, mitochondrial and nuclear, which evolve in very different ways. Serious incompatibilities between these genomes can have severe effects on development, fitness and viability. The effect of subtle mitonuclear mismatches has received less attention, especially when subject to mild physiological stress. Here, we investigate how two distinct physiological stresses, metabolic stress (high-protein diet) and redox stress [the glutathione precursor N-acetyl cysteine (NAC)], affect development time, egg-to-adult viability, and the mitochondrial physiology of Drosophila larvae with an isogenic nuclear background set against three mitochondrial DNA (mtDNA) haplotypes: one coevolved (WT) and two slightly mismatched (COX and BAR). Larvae fed the high-protein diet developed faster and had greater viability in all haplotypes. The opposite was true of NAC-fed flies, especially those with the COX haplotype. Unexpectedly, the slightly mismatched BAR larvae developed fastest and were the most viable on both treatments, as well as control diets. These changes in larval development were linked to a shift to complex I-driven mitochondrial respiration in all haplotypes on the high-protein diet. In contrast, NAC increased respiration in COX larvae but drove a shift toward oxidation of proline and succinate. The flux of reactive oxygen species was increased in COX larvae treated with NAC and was associated with an increase in mtDNA copy number. Our results support the notion that subtle mitonuclear mismatches can lead to diverging responses to mild physiological stress, undermining fitness in some cases, but surprisingly improving outcomes in other ostensibly mismatched fly lines
The Diabolo photometer and the future of ground-based millimetric bolometer devices
The millimetric atmospheric windows at 1 and 2 mm are interesting targets for
cosmological studies. Two broad areas appear leading this field: 1) the search
for high redshift star-forming galaxies and 2) the measurement of
Sunyaev-Zel'dovich (SZ) effect in clusters of galaxies at all redshifts. The
Diabolo photometer is a dual-channel photometer working at 1.2 and 2.1 mm and
dedicated to high angular resolution measurements of the Sunyaev--Zel'dovich
effect towards distant clusters. It uses 2 by 3 bolometers cooled down to 0.1 K
with a compact open dilution cryostat. The high resolution is provided by the
IRAM 30 m telescope. The result of several Winter campaigns are reported here,
including the first millimetric map of the SZ effect that was obtained by
Pointecouteau et al. (2001) on RXJ1347-1145, the non-detection of a millimetric
counterpart to the radio decrement towards PC1643+4631 and 2 mm number count
upper limits. We discuss limitations in ground-based single-dish millimetre
observations, namely sky noise and the number of detectors. We advocate the use
of fully sampled arrays of (100 to 1000) bolometers as a big step forward in
the millimetre continuum science. Efforts in France are briefly mentionned.Comment: 7 pages, 6 figures, to appear in the Proceedings of the 2K1BC
``Experimental Astronomy at millimeter wavelengths'', Breuil-Cervinia (AO)
Italy - July 9 - 13, 2001, Eds. M. De Petris et a
Mother's curse is pervasive across a large mitonuclear Drosophila panel
The maternal inheritance of mitochondrial genomes entails a sex-specific selective sieve, whereby mutations in mitochondrial DNA
can only respond to selection acting on females. In theory, this enables male-harming mutations to accumulate in mitochondrial
genomes as long as they are neutral, beneficial, or only slightly deleterious to females. Ultimately, this bias could drive the evolution
of male-specific mitochondrial mutation loads, an idea known as mother’s curse. Earlier work on this hypothesis has mainly used
small Drosophila panels, in which naturally sourced mitochondrial genomes were coupled to an isogenic nuclear background. The
lack of nuclear genetic variation in these designs has precluded robust generalization. Here, we test the predictions of mother’s
curse using a large Drosophila mitonuclear genetic panel, comprising nine isogenic nuclear genomes coupled to nine mitochondrial
haplotypes, giving a total of 81 different mitonuclear genotypes. Following a predictive framework, we tested the mother’s curse
hypothesis by screening our panel for wing size. This trait is tightly correlated with overall body size and is sexually dimorphic in
Drosophila. Moreover, growth is heavily reliant on metabolism and mitochondrial function, making wing size an ideal trait for the
study of the impact of mitochondrial variation. We detect high levels of mitonuclear epistasis, and more importantly, we report
that mitochondrial genetic variance is larger in male than female Drosophila for eight out of the nine nuclear genetic backgrounds
used. These results demonstrate that the maternal inheritance of mitochondrial DNA does indeed modulate male life history traits
in a more generalisable way than previously demonstrated
High temporal variability in the occurrence of consumer-resource interactions in ecological networks
Ecological networks are theoretical abstractions that represent ecological
communities. These networks are usually defined as static entities, in which
the occurrence of a particular interaction between species is considered fixed
despite the intrinsic dynamics of ecological systems. However, empirical
analysis of the temporal variation of trophic interactions is constrained by
the lack of data with high spatial, temporal, and taxonomic resolution. Here,
we evaluate the spatiotemporal variability of multiple consumer-resource
interactions of large marine networks. The tropic interactions of all of the
analyzed networks had low temporal persistence, which was well described by a
common exponential decay in the rank-frequency relationship of
consumer-resource interactions. This common pattern of low temporal persistence
was evident despite the dissimilarities of environmental conditions among
sites. Between-site rank correlations of frequency of occurrence of
interactions ranged from 0.59 to 0.73. After removing the interactions with
<50% frequency, the between-site correlations decreased to values between 0.60
and 0.28, indicating that low-frequency interactions accounted for the apparent
similarities between sites. Our results showed that the communities studied
were characterized by few persistent interactions and a large number of
transient trophic interactions. We suggest that consumer-resource temporal
asynchrony in addition to varying local environmental conditions and
opportunistic foraging could be among the mechanisms generating the observed
rank-frequency relationship of trophic interactions. Therefore, our results
question the analysis of ecological communities as static and persistent
natural entities and stress the need for strengthening the analysis of temporal
variability in ecological networks and long-term studies.Comment: 21 pages, 3 figure
Charting the New Frontier of the Cosmic Microwave Background Polarization
The anisotropies of the cosmic microwave background are a gold mine for
cosmology and fundamental physics. ESA's Planck satellite should soon extract
all information from the temperature vein but will be limited concerning the
measurement of the degree of polarization of the anisotropies. This
polarization information allows new independent tests of the standard
cosmological paradigm, improves knowledge of cosmological parameters and last
but not least is the best window available for constraining the physics of the
very early universe, particularly the expected background of primordial
gravitational waves. But exploiting this vein will be a challenge, since the
sensitivity required is {\em at least} 10 times better than what Planck might
achieve at best, with the necessary matching level of control of all
systematics effects, both instrumental and astrophysical (foregrounds). We here
recall the cosmological context and the case for CMB polarization studies. We
also briefly introduce the SAMPAN project, a design study at CNES that aims at
detecting the primoridal gravitational wave background for a tensor to scalar
ratio T/S as small as 0.001.Comment: 4 pages, to appear in SF2A 2005 proceeding
CHC22 and CHC17 clathrins have distinct biochemical properties and display differential regulation and function
Clathrins are cytoplasmic proteins that play essential roles in endocytosis and other membrane traffic pathways. Upon recruitment to intracellular membranes, the canonical clathrin triskelion assembles into a polyhedral protein coat that facilitates vesicle formation and captures cargo molecules for transport. The triskelion is formed by trimerization of three clathrin heavy-chain subunits. Most vertebrates have two isoforms of clathrin heavy chains, CHC17 and CHC22, generating two clathrins with distinct cellular functions. CHC17 forms vesicles at the plasma membrane for receptor-mediated endocytosis and at the trans-Golgi network for organelle biogenesis. CHC22 plays a key role in intracellular targeting of the insulin-regulated glucose transporter 4 (GLUT4), accumulates at the site of GLUT4 sequestration during insulin resistance, and has also been implicated in neuronal development. Here, we demonstrate that CHC22 and CHC17 share morphological features, in that CHC22 forms a triskelion and latticed vesicle coats. However, cellular CHC22-coated vesicles were distinct from those formed by CHC17. The CHC22 coat was more stable to pH change and was not removed by the enzyme complex that disassembles the CHC17 coat. Moreover, the two clathrins were differentially recruited to membranes by adaptors, and CHC22 did not support vesicle formation or transferrin endocytosis at the plasma membrane in the presence or absence of CHC17. Our findings provide biochemical evidence for separate regulation and distinct functional niches for CHC17 and CHC22 in human cells. Furthermore, the greater stability of the CHC22 coat relative to the CHC17 coat may be relevant to its excessive accumulation with GLUT4 during insulin resistance. [Abstract copyright: Copyright © 2017, The American Society for Biochemistry and Molecular Biology.
Evolution of dopant-induced helium nanoplasmas
Two-component nanoplasmas generated by strong-field ionization of doped
helium nanodroplets are studied in a pump-probe experiment using few-cycle
laser pulses in combination with molecular dynamics simulations. High yields of
helium ions and a pronounced, droplet size-dependent resonance structure in the
pump-probe transients reveal the evolution of the dopant-induced helium
nanoplasma. The pump-probe dynamics is interpreted in terms of strong inner
ionization by the pump pulse and resonant heating by the probe pulse which
controls the final charge states detected via the frustration of electron-ion
recombination
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