253 research outputs found
Five dimensional relativity and two times
It is possible that null paths in 5D appear as the timelike paths of massive
particles in 4D, where there is an oscillation in the fifth dimension around
the hypersurface we call spacetime. A particle in 5D may be regarded as
multiply imaged in 4D, and the 4D weak equivalence principle may be regarded as
a symmetry of the 5D metric.Comment: 15 pages, in press in Phys. Lett.
Sexual selection in mushroom-forming basidiomycetes
We expect that sexual selection may play an important role in the evolution of mushroom-forming basidiomycete fungi. Although these fungi do not have separate sexes, they do play female and male roles: the acceptance and the donation of a nucleus, respectively. The primary mycelium (monokaryon) of basidiomycete fungi, growing from a germinating sexual spore, is hermaphroditic, but it loses female function upon the acceptance of a second nucleus. The resulting dikaryon with two different nuclei in each cell retains a male potential as both nuclei can fertilize receptive mycelia. We tested the occurrence of sexual selection in the model species of mushroom-forming basidiomycetes, Schizophyllum commune, by pairing monokaryons with fully compatible dikaryons. In most pairings, we found a strong bias for one of the two nuclei although both were compatible with the monokaryon when paired alone. This shows that sexual selection can occur in mushroom-forming basidiomycetes. Since the winning nucleus of a dikaryon occasionally varied depending on the receiving monokaryon, we infer that sexual selection can operate through choosiness of the receiving individual (analogous to female choice). However, in other cases the same nucleus won, irrespective of the receiving monokaryon, suggesting that competition between the two nuclei of the donating mycelium (analogous to male–male competition) might also play a role
Effect-Directed Analysis of Municipal Landfill Soil Reveals Novel Developmental Toxicants in the Zebrafish Danio rerio
Effect-directed analysis (EDA) is an approach used to identify (unknown) contaminants in complex samples which cause toxicity, using a combination of biology and chemistry. The goal of this work was to apply EDA to identify developmental toxicants in soil samples collected from a former municipal landfill site. Soil samples were extracted, fractionated, and tested for developmental effects with an embryotoxicity assay in the zebrafish Danio rerio. Gas chromatograph mass selective detection (GC-MSD) chemical screening was used to reveal candidate developmental toxicants in fractions showing effects. In a parallel study, liquid chromatography-hybrid linear ion trap Orbitrap mass spectrometry was also applied to one polar subfraction (Hoogenboom et al. J. Chromatogr. A2009, 1216, 510-519). EDA resulted in the identification of a number of previously unknown developmental toxicants, which were confirmed to be present in soil by GC-MS. These included 11H-benzo[b]fluorene, 9-methylacridine, 4-azapyrene, and 2-phenylquinoline, as well as one known developmental toxicant (retene). This work revealed the presence of novel contaminants in the environment that may affect vertebrate development, which are not subject to monitoring or regulation under current soil quality assessment guidelines. © 2011 American Chemical Society
Neurospora from natural populations: Population genomics insights into the Life history of a model microbial Eukaryote
The ascomycete filamentous fungus Neurospora crassa played a historic role in experimental biology and became a model system for genetic research. Stimulated by a systematic effort to collect wild strains initiated by Stanford geneticist David Perkins, the genus Neurospora has also become a basic model for the study of evolutionary processes, speciation, and population biology. In this chapter, we will first trace the history that brought Neurospora into the era of population genomics. We will then cover the major contributions of population genomic investigations using Neurospora to our understanding of microbial biogeography and speciation, and review recent work using population genomics and genome-wide association mapping that illustrates the unique potential of Neurospora as a model for identifying the genetic basis of (potentially adaptive) phenotypes in filamentous fungi. The advent of population genomics has contributed to firmly establish Neurospora as a complete model system and we hope our review will entice biologists to include Neurospora in their research
Repeated evolution of self-compatibility for reproductive assurance
Sexual reproduction in eukaryotes requires the fusion of two compatible gametes of opposite sexes or mating types. To meet the challenge of finding a mating partner with compatible gametes evolutionary mechanisms such as hermaphroditism and self-fertilisation have repeatedly evolved. Combining insight from comparative genomics, computer simulations and experimental evolution in fission yeast, we shed light on the conditions promoting separate mating types or self-compatibility by mating-type switching. Analogous to multiple independent transitions between switchers and non-switchers in natural populations mediated by structural genomic changes, novel switching genotypes were readily evolving under selection in experimental populations. Detailed fitness measurements accompanied by computer simulations show the benefits and costs of switching during sexual and asexual reproduction governing the occurrence of both strategies in nature. Our findings illuminate the trade-off between the benefits of reproductive assurance and its fitness costs under benign conditions governing the evolution of self-compatibility
An unusual occurrence of Kleine-Levin syndrome in a man with refractory immune thrombocytopenic purpura: a case report
Reduced cytochrome P4501A activity and recovery from oxidative stress during subchronic benzo[a]pyrene and benzo[e]pyrene treatment of rainbow trout
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Toxicology and Applied Pharmacology 254 (2011): 1-7, doi:10.1016/j.taap.2011.04.015.This
study
assessed
the
role
of
aryl
hydrocarbon
receptor
(AHR)
affinity,
and
cytochrome
P4501A
(CYP1A)
protein
and
activity
in
polyaromatic
hydrocarbon
(PAH)-‐induced
oxidative
stress.
In
the
1-‐100
nM
concentration
range
benzo[a]pyrene
(BaP)
but
not
benzo[e]pyrene
(BeP)
competitively
displaced
2
nM
[3H]2,
3,
7,
8-‐tetrachloro-‐dibenzo-‐p-‐dioxin
from
rainbow
trout
AHR2α.
Based
on
appearance
of
fluorescent
aromatic
compounds
in
bile
over
3,
7,
14,
28
or
50
days
of
feeding
3
μg
of
BaP
or
BeP/g
fish/day,
rainbow
trout
liver
readily
excreted
these
polyaromatic
hydrocarbons
(PAHs)
and
their
metabolites
at
near
steady
state
rates.
CYP1A
proteins
catalyzed
more
than
98%
of
ethoxyresorufin-‐O-‐deethylase
(EROD)
activity
in
rainbow
trout
hepatic
microsomes.
EROD
activity
of
hepatic
microsomes
initially
increased
and
then
decreased
to
control
activities
after
50
days
of
feeding
both
PAHs.
Immunohistochemistry
of
liver
confirmed
CYP1A
protein
increased
in
fish
fed
both
PAHs
after
3
days
and
remained
elevated
for
up
to
28
days.
Neither
BaP
nor
BeP
increased
hepatic
DNA
adduct
concentrations
at
any
time
up
to
50
days
of
feeding
these
PAHs.
Comet
assays
of
blood
cells
demonstrated
marked
DNA
damage
after
14
days
of
feeding
both
PAHs
that
was
not
significant
after
50
days.
There
was
a
strong
positive
correlation
between
hepatic
EROD
activity
and
DNA
damage
in
blood
cells
over
time
for
both
PAHs.
Neither
CYP1A
protein
nor
3-‐
nitrotyrosine
(a
biomarker
for
oxidative
stress)
immunostaining
in
trunk
kidney
were
significantly
altered
by
BaP
or
BeP
after
3,
7,
14,
or
28
days.
There
was
no
clear
association
between
AHR2α
affinity
and
BaP
and
BeP-‐induced
oxidative
stress.The
Oregon
Agricultural
Experiment
Station,
Northwest
Fisheries
Science
Center,
and
RO1ES006272
from
the
National
Institute
of
Health
supported
this
work
Ror2 modulates the canonical Wnt signaling in lung epithelial cells through cooperation with Fzd2
<p>Abstract</p> <p>Background</p> <p>Wnt signaling is mediated through 1) the beta-catenin dependent canonical pathway and, 2) the beta-catenin independent pathways. Multiple receptors, including Fzds, Lrps, Ror2 and Ryk, are involved in Wnt signaling. Ror2 is a single-span transmembrane receptor-tyrosine kinase (RTK). The functions of Ror2 in mediating the non-canonical Wnt signaling have been well established. The role of Ror2 in canonical Wnt signaling is not fully understood.</p> <p>Results</p> <p>Here we report that Ror2 also positively modulates Wnt3a-activated canonical signaling in a lung carcinoma, H441 cell line. This activity of Ror2 is dependent on cooperative interactions with Fzd2 but not Fzd7. In addition, Ror2-mediated enhancement of canonical signaling requires the extracellular CRD, but not the intracellular PRD domain of Ror2. We further provide evidence that the positive effect of Ror2 on canonical Wnt signaling is inhibited by Dkk1 and Krm1 suggesting that Ror2 enhances an Lrp-dependent STF response.</p> <p>Conclusion</p> <p>The current study demonstrates the function of Ror2 in modulating canonical Wnt signaling. These findings support a functional scheme whereby regulation of Wnt signaling is achieved by cooperative functions of multiple mediators.</p
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