251 research outputs found
Common and Distinct Roles of Juvenile Hormone Signaling Genes in Metamorphosis of Holometabolous and Hemimetabolous Insects
Insect larvae metamorphose to winged and reproductive adults either directly (hemimetaboly) or through an intermediary pupal stage (holometaboly). In either case juvenile hormone (JH) prevents metamorphosis until a larva has attained an appropriate phase of development. In holometabolous insects, JH acts through its putative receptor Methoprene-tolerant (Met) to regulate Krüppel-homolog 1 (Kr-h1) and Broad-Complex (BR-C) genes. While Met and Kr-h1 prevent precocious metamorphosis in pre-final larval instars, BR-C specifies the pupal stage. How JH signaling operates in hemimetabolous insects is poorly understood. Here, we compare the function of Met, Kr-h1 and BR-C genes in the two types of insects. Using systemic RNAi in the hemimetabolous true bug, Pyrrhocoris apterus, we show that Met conveys the JH signal to prevent premature metamorphosis by maintaining high expression of Kr-h1. Knockdown of either Met or Kr-h1 (but not of BR-C) in penultimate-instar Pyrrhocoris larvae causes precocious development of adult color pattern, wings and genitalia. A natural fall of Kr-h1 expression in the last larval instar normally permits adult development, and treatment with an exogenous JH mimic methoprene at this time requires both Met and Kr-h1 to block the adult program and induce an extra larval instar. Met and Kr-h1 therefore serve as JH-dependent repressors of deleterious precocious metamorphic changes in both hemimetabolous and holometabolous juveniles, whereas BR-C has been recruited for a new role in specifying the holometabolous pupa. These results show that despite considerable evolutionary distance, insects with diverse developmental strategies employ a common-core JH signaling pathway to commit to adult morphogenesis
The Gonium pectorale genome demonstrates co-option of cell cycle regulation during the evolution of multicellularity
Citation: Hanschen, E. R., Marriage, T. N., Ferris, P. J., Hamaji, T., Toyoda, A., Fujiyama, A., . . . Olson, B. (2016). The Gonium pectorale genome demonstrates co-option of cell cycle regulation during the evolution of multicellularity. Nature Communications, 7, 10. doi:10.1038/ncomms11370Additional Authors: Anderson, J.;Bakaric, R.;Luria, V.;Karger, A.;Kirschner, M. W.;Durand, P. M.;Michod, R. E.;Nozaki, H.The transition to multicellularity has occurred numerous times in all domains of life, yet its initial steps are poorly understood. The volvocine green algae are a tractable system for understanding the genetic basis of multicellularity including the initial formation of cooperative cell groups. Here we report the genome sequence of the undifferentiated colonial alga, Gonium pectorale, where group formation evolved by co-option of the retinoblastoma cell cycle regulatory pathway. Significantly, expression of the Gonium retinoblastoma cell cycle regulator in unicellular Chlamydomonas causes it to become colonial. The presence of these changes in undifferentiated Gonium indicates extensive group-level adaptation during the initial step in the evolution of multicellularity. These results emphasize an early and formative step in the evolution of multicellularity, the evolution of cell cycle regulation, one that may shed light on the evolutionary history of other multicellular innovations and evolutionary transitions
Lamb wave ultrasonic evaluation of welded AA2024 specimens at tensile static and fatigue testing
The paper deals with the investigation of Lamb waves ultrasonic testing technique applied for evaluation of different stress-strain and damaged state of aluminum specimens at static and fatigue loading in order to develop a Structural Health Monitoring (SHM) approach. The experimental results of tensile testing of AA2024T3 specimens with welded joints are presented. Piezoelectric transducers used as actuators and sensors were adhesively bonded to the specimen's surface using two component epoxy. The set of static and cyclic tensile tests with two frequencies of acoustic testing (50 kHz and 335 kHz) were performed. The recorded signals were processed to calculate the maximum envelope in order to evaluate the changes of the stress-strain state of the specimen and its microstructure during static tension. The registered data are analyzed and discussed in terms of signal attenuation due to the formation of fatigue defects during cyclic loading. Understanding the relations between acoustic signal features and fatigue damages will provide us the ability to determine the damage state of the structure and its residual lifetime in order to design a robust SHM system
Landau level mixing and spin degeneracy in the quantum Hall effect
We study dynamics of electrons in a magnetic field using a network model with
two channels per link with random mixing in a random intrachannel potential;
the channels represent either two Landau levels or two spin states. We consider
channel mixing as function of the energy separation of the two extended states
and show that its effect changes from repulsion to attraction as the energy
separation increases. For two Landau levels this leads to level floating at low
magnetic fields while for Zeeman split spin states we predict level attraction
at high magnetic fields, accounting for ESR data. We also study random mixing
of two degenerate channels, while the intrachannel potential is periodic
(non-random). We find a single extended state with a localization exponent
for real scattering at nodes; the general case has also a
single extended state, though the localized nature of nearby states sets in at
unusually large scales.Comment: 18 pages, 11 tex-files and 1 ps-file of figure
Metal-insulator transition in two-dimensional disordered systems with power-law transfer terms
We investigate a disordered two-dimensional lattice model for noninteracting
electrons with long-range power-law transfer terms and apply the method of
level statistics for the calculation of the critical properties. The
eigenvalues used are obtained numerically by direct diagonalization. We find a
metal-insulator transition for a system with orthogonal symmetry. The exponent
governing the divergence of the correlation length at the transition is
extracted from a finite size scaling analysis and found to be . The critical eigenstates are also analyzed and the distribution of the
generalized multifractal dimensions is extrapolated.Comment: 4 pages with 4 figures, printed version: PRB, Rapid Communication
Genome-Wide Survey and Expression Analysis Suggest Diverse Roles of Glutaredoxin Gene Family Members During Development and Response to Various Stimuli in Rice
Glutaredoxins (GRXs) are glutathione-dependent oxidoreductase enzymes involved in a variety of cellular processes. In this study, our analysis revealed the presence of 48 genes encoding GRX proteins in the rice genome. GRX proteins could be classified into four classes, namely CC-, CGFS-, CPYC- and GRL-type, based on phylogenetic analysis. The classification was supported with organization of predicted conserved putative motifs in GRX proteins. We found that expansion of this gene family has occurred largely via whole genome duplication events in a species-specific manner. We explored rice oligonucleotide array data to gain insights into the function of GRX gene family members during various stages of development and in response to environmental stimuli. The comprehensive expression analysis suggested diverse roles of GRX genes during growth and development in rice. Some of the GRX genes were expressed in specific organs/developmental stages only. The expression of many of rice GRX genes was influenced by various phytohormones, abiotic and biotic stress conditions, suggesting an important role of GRX proteins in response to these stimuli. The identification of GRX genes showing differential expression in specific tissues or in response to environmental stimuli provide a new avenue for in-depth characterization of selected genes of importance
The random magnetic flux problem in a quantum wire
The random magnetic flux problem on a lattice and in a quasi one-dimensional
(wire) geometry is studied both analytically and numerically. The first two
moments of the conductance are obtained analytically. Numerical simulations for
the average and variance of the conductance agree with the theory. We find that
the center of the band plays a special role. Away from
, transport properties are those of a disordered quantum wire in
the standard unitary symmetry class. At the band center , the
dependence on the wire length of the conductance departs from the standard
unitary symmetry class and is governed by a new universality class, the chiral
unitary symmetry class. The most remarkable property of this new universality
class is the existence of an even-odd effect in the localized regime:
Exponential decay of the average conductance for an even number of channels is
replaced by algebraic decay for an odd number of channels.Comment: 16 pages, RevTeX; 9 figures included; to appear in Physical Review
Crossover from the chiral to the standard universality classes in the conductance of a quantum wire with random hopping only
The conductance of a quantum wire with off-diagonal disorder that preserves a
sublattice symmetry (the random hopping problem with chiral symmetry) is
considered. Transport at the band center is anomalous relative to the standard
problem of Anderson localization both in the diffusive and localized regimes.
In the diffusive regime, there is no weak-localization correction to the
conductance and universal conductance fluctuations are twice as large as in the
standard cases. Exponential localization occurs only for an even number of
transmission channels in which case the localization length does not depend on
whether time-reversal and spin rotation symmetry are present or not. For an odd
number of channels the conductance decays algebraically. Upon moving away from
the band center transport characteristics undergo a crossover to those of the
standard universality classes of Anderson localization. This crossover is
calculated in the diffusive regime.Comment: 22 pages, 9 figure
Integer Quantum Hall Effect in Double-Layer Systems
We consider the localization of independent electron orbitals in double-layer
two-dimensional electron systems in the strong magnetic field limit. Our study
is based on numerical Thouless number calculations for realistic microscopic
models and on transfer matrix calculations for phenomenological network models.
The microscopic calculations indicate a crossover regime for weak interlayer
tunneling in which the correlation length exponent appears to increase.
Comparison of network model calculations with microscopic calculations casts
doubt on their generic applicability.Comment: 14 pages, 12 figures included, RevTeX 3.0 and epsf. Additional
reference
- …