bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitation–contraction uncoupling by a human central core disease mutation in the ryanodine receptor
Authors: Avila Guillermo , O'Brien Jennifer J. , Dirksen Robert T.
Published: July 2002

Central core disease (CCD) is a human congenital myopathy
characterized by fetal hypotonia and proximal muscle weakness that is
linked to mutations in the gene encoding the type-1 ryanodine receptor
(RyR1). CCD is thought to arise from Ca
2+
-induced damage
stemming from mutant RyR1 proteins forming “leaky” sarcoplasmic
reticulum (SR) Ca
2+
release channels. A novel mutation in
the C-terminal region of RyR1 (I4898T) accounts for an unusually severe
and highly penetrant form of CCD in humans [Lynch, P. J., Tong,
J., Lehane, M., Mallet, A., Giblin, L., Heffron, J. J., Vaughan,
P., Zafra, G., MacLennan, D. H. & McCarthy, T. V. (1999)
Proc. Natl. Acad. Sci. USA
96, 4164–4169]. We
expressed in skeletal myotubes derived from RyR1-knockout (dyspedic)
mice the analogous mutation engineered into a rabbit RyR1 cDNA
(I4897T). Here we show that homozygous expression of I4897T in dyspedic
myotubes results in a complete uncoupling of sarcolemmal excitation
from voltage-gated SR Ca
2+
release without significantly
altering resting cytosolic Ca
2+
levels, SR Ca
2+
content, or RyR1-mediated enhancement of dihydropyridine receptor
(DHPR) channel activity. Coexpression of both I4897T and wild-type RyR1
resulted in a 60% reduction in voltage-gated SR Ca
2+
release, again without altering resting cytosolic Ca
2+
levels, SR Ca
2+
content, or DHPR channel activity. These
findings indicate that muscle weakness suffered by individuals
possessing the I4898T mutation involves a functional uncoupling of
sarcolemmal excitation from SR Ca
2+
release, rather than
the expression of overactive or leaky SR Ca
2+
release
channels.
Sialylation is essential for early development in mice
Authors: Schwarzkopf Martina , Knobeloch Klaus-Peter , Rohde Elvira , Hinderlich Stephan , Wiechens Nicola , Lucka Lothar , Horak Ivan , Reutter Werner , Horstkorte Rüdiger
Published: July 2002

Sialic acids are widely expressed as terminal carbohydrates on glycoconjugates of eukaryotic cells. Sialylation is crucial for a variety of cellular functions, such as cell adhesion or signal recognition, and regulates the biological stability of glycoproteins. The key enzyme of sialic acid biosynthesis is the bifunctional UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (UDP-GlcNAc 2-epimerase), which catalyzes the first two steps of sialic acid biosynthesis in the cytosol. We report that inactivation of the UDP-GlcNAc 2-epimerase by gene targeting causes early embryonic lethality in mice, thereby emphasizing the fundamental role of this bifunctional enzyme and sialylation during development. The need of UDP-GlcNAc 2-epimerase for a defined sialylation process is exemplified with the polysialylation of the neural cell adhesion molecule in embryonic stem cells.
Influences of aging and caloric restriction on the transcriptional profile of skeletal muscle from rhesus monkeys
Authors: Kayo Tsuyoshi , Allison David B. , Weindruch Richard , Prolla Tomas A.
Published: July 2002

In laboratory rodents, caloric restriction (CR) retards
several age-dependent physiological and biochemical changes in skeletal
muscle, including increased steady-state levels of oxidative damage to
lipids, DNA, and proteins. We have previously used high-density
oligonucleotide arrays to show that CR can prevent or delay most of the
major age-related transcriptional alterations in the gastrocnemius
muscle of C57BL/6 mice. Here we report the effects of aging and
adult-onset CR on the gene expression profile of 7,070 genes in the
vastus lateralis muscle from rhesus monkeys. Gene expression analysis
of aged rhesus monkeys (mean age of 26 years) was compared with that of
young animals (mean age of 8 years). Aging resulted in a selective
up-regulation of transcripts involved in inflammation and oxidative
stress, and a down-regulation of genes involved in mitochondrial
electron transport and oxidative phosphorylation. Middle-aged monkeys
(mean age of 20 years) subjected to CR since early adulthood (mean age
of 11 years) were studied to determine the gene expression profile
induced by CR. CR resulted in an up-regulation of cytoskeletal
protein-encoding genes, and also a decrease in the expression of genes
involved in mitochondrial bioenergetics. Surprisingly, we did not
observe any evidence for an inhibitory effect of adult-onset CR on
age-related changes in gene expression. These results indicate that the
induction of an oxidative stress-induced transcriptional response may
be a common feature of aging in skeletal muscle of rodents and
primates, but the extent to which CR modifies these responses may be
species-specific.
A simple model of global cascades on random networks
Authors: Watts Duncan J.
Published: July 2002

The origin of large but rare cascades that are triggered by small initial shocks is a phenomenon that manifests itself as diversely as cultural fads, collective action, the diffusion of norms and innovations, and cascading failures in infrastructure and organizational networks. This paper presents a possible explanation of this phenomenon in terms of a sparse, random network of interacting agents whose decisions are determined by the actions of their neighbors according to a simple threshold rule. Two regimes are identified in which the network is susceptible to very large cascades—herein called global cascades—that occur very rarely. When cascade propagation is limited by the connectivity of the network, a power law distribution of cascade sizes is observed, analogous to the cluster size distribution in standard percolation theory and avalanches in self-organized criticality. But when the network is highly connected, cascade propagation is limited instead by the local stability of the nodes themselves, and the size distribution of cascades is bimodal, implying a more extreme kind of instability that is correspondingly harder to anticipate. In the first regime, where the distribution of network neighbors is highly skewed, it is found that the most connected nodes are far more likely than average nodes to trigger cascades, but not in the second regime. Finally, it is shown that heterogeneity plays an ambiguous role in determining a system's stability: increasingly heterogeneous thresholds make the system more vulnerable to global cascades; but an increasingly heterogeneous degree distribution makes it less vulnerable.
The root of the angiosperms revisited
Authors: Zanis Michael J. , Soltis Douglas E. , Soltis Pamela S. , Mathews Sarah , Donoghue Michael J.
Published: July 2002

Most recent phylogenetic analyses of basal angiosperms have converged on the placement ofAmborellaas sister to all other extant angiosperms. However, certain recent studies suggest thatAmborellaand Nymphaeales (water lilies) form a clade sister to all remaining angiosperms or that Nymphaeales alone are the sister to the remaining angiosperms. We report here (i) maximum parsimony, maximum likelihood, and Bayesian phylogenetic analyses of 11 genes (>15,000 bp per taxon) for 16 taxa, (ii) maximum parsimony analysis for a subset of these genes for 104 taxa, and (iii) tests of alternative rootings with the nonparametric bootstrap and the likelihood ratio test with the parametric bootstrap. In addition, we use simulation analyses to examine the amount of bias that may be present in our methods of phylogeny estimation.Amborellacontinues to receive strong bootstrap support as the sister to all other extant angiosperms, and three of four tests reject alternative hypotheses of the angiosperm root. Although we cannot conclusively choose betweenAmborellavs.Amborella+ Nymphaeales as sister to all other angiosperms, most analyses favor the former rooting.
Dental microstructure and life history in subfossil Malagasy lemurs
Authors: Schwartz Gary T. , Samonds Karen E. , Godfrey Laurie R. , Jungers William L. , Simons Elwyn L.
Published: July 2002

When compared with their recently extinct relatives, living lemurs represent a mere fraction of a broad radiation that occupied unique niches in the recent past. Among living lemurs, indrids exhibit the fastest rates of dental development. This dental precocity is tightly correlated with rapid pace of postnatal dental eruption, early replacement of the deciduous teeth, high dental endowment at weaning, and relatively slow somatic growth. This pattern is in stark contrast to that seen in extant lemurids, where somatic development is highly accelerated and dental development is relatively slow. We report on the pace of dental development in one species of palaeopropithecid, the sister group to extant indrids. Like much smaller modern indrids, the chimpanzee-sized
Palaeopropithecus ingens
was dentally precocious at birth as evidenced by the advanced state of molar crown formation. This finding implies a pattern characteristic of
Propithecus
and other indrids—rapid dental development despite relatively prolonged gestation. Gestation length in this one species of subfossil lemur was likely greater than 9 months. Our results demonstrate that large body size in primates does not preclude exceedingly rapid dental development.
Pseudoxanthoma elasticum: Mutations in the
MRP6
gene encoding a transmembrane ATP-binding cassette (ABC) transporter
Authors: Ringpfeil Franziska , Lebwohl Mark G. , Christiano Angela M. , Uitto Jouni
Published: July 2002

Pseudoxanthoma elasticum (PXE), the prototypic heritable connective tissue disorder affecting the elastic structures in the body, manifests with cutaneous, ophthalmologic, and cardiovascular findings, with considerable morbidity and mortality. The molecular basis of PXE has remained unknown, but the disease locus has recently been mapped to an ≈500-kb interval on chromosome 16p13.1, without evidence for locus heterogeneity. In this study, we report pathogenetic mutations in
MRP6
, a member of the ABC transporter gene family, in eight kindreds with PXE. The mutation detection strategy consisted of heteroduplex scanning of coding sequences in the
MRP6
gene, which were amplified by PCR by using genomic DNA as template, followed by direct nucleotide sequencing. A total of 13 mutant
MRP6
alleles were disclosed in the eight probands with PXE. These genetic lesions consisted of either single base pair substitutions resulting in missense, nonsense, or splice site mutations, or large deletions resulting in allelic loss of the
MRP6
locus. Examination of clinically unaffected family members in four multiplex families identified heterozygous carriers, consistent with an autosomal recessive inheritance pattern. Collectively, identification of mutations in the
MRP6
gene provides the basis to examine the pathomechanisms of PXE and allows development of DNA-based carrier detection, prenatal testing, and preimplantation genetic diagnosis in families with a history of this disease.
Protein oxidation in response to increased transcriptional or translational errors
Authors: Dukan S. , Farewell A. , Ballesteros M. , Taddei F. , Radman M. , Nyström T.
Published: July 2002

In this study, we show a correlation between synthesis of aberrant proteins and their oxidative modification. The level of aberrant proteins was elevated in
Escherichia coli
cultures by decreasing transcriptional or translational fidelity using specific mutations or drugs. Protein carbonylation, an oxidative modification, increased in parallel to the induction of the heat shock chaperone GroEL. As the protein turnover rates and level of intracellular oxidative stress remained unchanged, it appears that carbonylation results from the increased susceptibility of the misfolded proteins. These studies show that the cellular protein oxidation is not limited only by available reactive oxygen species, but by the levels of aberrant proteins. Thus, protein oxidation seen in aging cells may be the consequence also of reduced transcriptional/translational fidelity, and protein structures appear to have evolved to minimize oxidative damage. In addition, we discuss the possibility that carbonylation, being an unrepairable protein modification, may serve as a tagging system to shunt misfolded proteins between pathways of refolding by chaperones or the proteolytic apparatus.
Ecosystem impacts of three sequential hurricanes (Dennis, Floyd, and Irene) on the United States' largest lagoonal estuary, Pamlico Sound, NC
Authors: Paerl Hans W. , Bales Jerad D. , Ausley Larry W. , Buzzelli Christopher P. , Crowder Larry B. , Eby Lisa A. , Fear John M. , Go Malia , Peierls Benjamin L. , Richardson Tammi L. , Ramus Joseph S.
Published: July 2002

Three sequential hurricanes, Dennis, Floyd, and Irene,
affected coastal North Carolina in September and October 1999. These
hurricanes inundated the region with up to 1 m of rainfall,
causing 50- to 500-year flooding in the watershed of the Pamlico Sound,
the largest lagoonal estuary in the United States and a key West
Atlantic fisheries nursery. We investigated the ecosystem-level impacts
on and responses of the Sound to the floodwater discharge. Floodwaters
displaced three-fourths of the volume of the Sound, depressed salinity
by a similar amount, and delivered at least half of the typical annual
nitrogen load to this nitrogen-sensitive ecosystem. Organic carbon
concentrations in floodwaters entering Pamlico Sound via a major
tributary (the Neuse River Estuary) were at least 2-fold higher than
concentrations under prefloodwater conditions. A cascading set of
physical, chemical, and ecological impacts followed, including strong
vertical stratification, bottom water hypoxia, a sustained increase in
algal biomass, displacement of many marine organisms, and a rise in
fish disease. Because of the Sound's long residence time (≈1 year),
we hypothesize that the effects of the short-term nutrient enrichment
could prove to be multiannual. A predicted increase in the frequency of
hurricane activity over the next few decades may cause longer-term
biogeochemical and trophic changes in this and other estuarine and
coastal habitats.
Nondestructive,in situ, cellular-scale mapping of elemental abundances including organic carbon in permineralized fossils
Authors: Boyce C. K. , Hazen R. M. , Knoll A. H.
Published: July 2002

The electron microprobe allows elemental abundances to be mapped at the μm scale, but until now high resolution mapping of light elements has been challenging. Modifications of electron microprobe procedure permit fine-scale mapping of carbon. When applied to permineralized fossils, this technique allows simultaneous mapping of organic material, major matrix-forming elements, and trace elements with μm-scale resolution. The resulting data make it possible to test taphonomic hypotheses for the formation of anatomically preserved silicified fossils, including the role of trace elements in the initiation of silica precipitation and in the prevention of organic degradation. The technique allows one to understand the localization of preserved organic matter before undertaking destructive chemical analyses and, because it is nondestructive, offers a potentially important tool for astrobiological investigations of samples returned from Mars or other solar system bodies.
Evidence for a dysfunctional prefrontal circuit in patients with an impulsive aggressive disorder
Authors: Best Mary , Williams J. Michael , Coccaro Emil F.
Published: July 2002

Humans with lesions to the orbital/medial prefrontal cortex and interconnected areas display impulsive aggressive behavior. To examine further the relationship between impulsive aggression and orbital/medial prefrontal dysfunction, we measured the behavioral performance of psychiatric patients with a disorder characterized by impulsive aggression, Intermittent Explosive Disorder (IED). Presently, no evidence exists for a localized brain lesion in IED subjects. However, on the basis of the location of brain lesions that produce acquired impulsive aggression, we hypothesized that IED subjects would exhibit test performance similar to patients with lesions to the orbital/medial prefrontal cortex. Subjects with IED and controls were administered three tests sensitive to lesions of the orbital/medial prefrontal circuit: the Iowa Gambling Task, facial emotion recognition, and odor identification, and two control tests of working memory. On the gambling task, IED subjects continued to make disadvantageous decisions throughout the 100 trials, whereas controls learned to avoid disadvantageous decisions. On the facial recognition test, IED subjects were impaired at recognizing “anger,” “disgust,” and “surprise,” and they were biased to label neutral faces with “disgust” and “fear.” On odor identification, IED subjects were mildly anosmic and were impaired relative to controls. However, on the working memory control tests, both groups performed similarly. Across tests, the performance of IED subjects resembles the performance of patients with orbital/medial prefrontal lesions in previous studies. These results extend the link between dysfunction of the orbital/medial prefrontal circuit and impulsive aggressive behavior.
The
Arabidopsis thaliana
salt tolerance gene
SOS1
encodes a putative Na
+
/H
+
antiporter
Authors: Shi Huazhong , Ishitani Manabu , Kim Cheolsoo , Zhu Jian-Kang
Published: July 2002

In
Arabidopsis thaliana
, the
SOS1
(
S
alt
O
verly
S
ensitive
1
) locus is essential for Na
+
and K
+
homeostasis, and
sos1
mutations render plants more sensitive to growth inhibition by high Na
+
and low K
+
environments.
SOS1
is cloned and predicted to encode a 127-kDa protein with 12 transmembrane domains in the N-terminal part and a long hydrophilic cytoplasmic tail in the C-terminal part. The transmembrane region of SOS1 has significant sequence similarities to plasma membrane Na
+
/H
+
antiporters from bacteria and fungi. Sequence analysis of various
sos1
mutant alleles reveals several residues and regions in the transmembrane as well as the tail parts that are critical for SOS1 function in plant salt tolerance.
SOS1
gene expression in plants is up-regulated in response to NaCl stress. This up-regulation is abated in
sos3
or
sos2
mutant plants, suggesting that it is controlled by the SOS3/SOS2 regulatory pathway.
Tracking wakes: The nocturnal predatory strategy of piscivorous catfish
Authors: Pohlmann Kirsten , Grasso Frank W. , Breithaupt Thomas
Published: July 2002

Swimming fish leave wakes containing hydrodynamic and chemical traces. These traces mark their swim paths and could guide predators. We now show that nocturnal European catfish (
Silurus glanis
) locate a piscine prey (guppy,
Poecilia reticulata
) by accurately tracking its three-dimensional swim path before an attack in the absence of visible light. Wakes that were up to 10 s old were followed over distances up to 55 prey-body lengths in our setup. These results demonstrate that prey wakes remain sufficiently identifiable to guide predators, and to extend considerably the area in which prey is detectable. Moreover, wakes elicit rear attacks, which may be more difficult to detect by prey. Wake tracking may be a common strategy among aquatic predators.
The change in oceanic O
2
inventory associated with recent global warming
Authors: Keeling Ralph F. , Garcia Hernan E.
Published: July 2002

Oceans general circulation models predict that global warming may cause a decrease in the oceanic O
2
inventory and an associated O
2
outgassing. An independent argument is presented here in support of this prediction based on observational evidence of the ocean's biogeochemical response to natural warming. On time scales from seasonal to centennial, natural O
2
flux/heat flux ratios are shown to occur in a range of 2 to 10 nmol of O
2
per joule of warming, with larger ratios typically occurring at higher latitudes and over longer time scales. The ratios are several times larger than would be expected solely from the effect of heating on the O
2
solubility, indicating that most of the O
2
exchange is biologically mediated through links between heating and stratification. The change in oceanic O
2
inventory through the 1990s is estimated to be 0.3 ± 0.4 × 10
14
mol of O
2
per year based on scaling the observed anomalous long-term ocean warming by natural O
2
flux/heating ratios and allowing for uncertainty due to decadal variability. Implications are discussed for carbon budgets based on observed changes in atmospheric O
2
/N
2
ratio and based on observed changes in ocean dissolved inorganic carbon.
Polymerase η deficiency in the xeroderma pigmentosum variant uncovers an overlap between the S phase checkpoint and double-strand break repair
Authors: Limoli Charles L. , Giedzinski Erich , Morgan William F. , Cleaver James E.
Published: July 2002

The xeroderma pigmentosum variant (XPV) is a genetic disease involving high levels of solar-induced cancer that has normal excision repair but shows defective DNA replication after UV irradiation because of mutations in the damage-specific polymerase hRAD30. We previously found that the induction of sister chromatid exchanges by UV irradiation was greatly enhanced in transformed XPV cells, indicating the activation of a recombination pathway. We now have identified that XPV cells make use of a homologous recombination pathway involving the hMre11/hRad50/Nbs1 protein complex, but not the Rad51 recombination pathway. The hMre11 complexes form at arrested replication forks, in association with proliferating cell nuclear antigen. In x-ray-damaged cells, in contrast, there is no association between hMre11 and proliferating cell nuclear antigen. This recombination pathway assumes greater importance in transformed XPV cells that lack a functional p53 pathway and can be detected at lower frequencies in excision-defective XPA fibroblasts and normal cells. DNA replication arrest after UV damage, and the associated S phase checkpoint, is therefore a complex process that can recruit a recombination pathway that has a primary role in repair of double-strand breaks from x-rays. The symptoms of elevated solar carcinogenesis in XPV patients therefore may be associated with increased genomic rearrangements that result from double-strand breakage and rejoining in cells of the skin in which p53 is inactivated by UV-induced mutations.
Gene genealogies reveal global phylogeographic structure and reproductive isolation among lineages of
Fusarium graminearum
, the fungus causing wheat scab
Authors: O'Donnell Kerry , Kistler H. Corby , Tacke Beth K. , Casper Howard H.
Published: July 2002

During the past decade, the plant disease called scab or
Fusarium
head blight of wheat and barley has reached epidemic proportions in North America and elsewhere in the world. Scab is an economically devastating plant disease, not only because it causes significant reduction in seed yields and quality, but also because infested seeds are often contaminated with trichothecene and estrogenic mycotoxins that pose a serious threat to animal health and food safety. To test whether the primary etiological agent of scab, the fungus
Fusarium graminearum
, is panmictic throughout its range, allelic genealogies were constructed from six single-copy nuclear genes from strains selected to represent the global genetic diversity of this pathogen. Excluding one hybrid strain, all six genealogies recovered the same seven biogeographically structured lineages, suggesting that they represent phylogenetically distinct species among which gene flow has been very limited during their evolutionary history. Parsimony analysis of the combined data set comprising 7,120 aligned nucleotide characters resolved most relationships among the seven lineages of the
F. graminearum
clade and related fusaria included in the study. Phylogenetic evidence is also presented for introgressive hybridization and intragenic recombination among lineages of the
F. graminearum
clade in nature.
Expression and functional significance of VE-cadherin in aggressive human melanoma cells: Role in vasculogenic mimicry
Authors: Hendrix Mary J. C. , Seftor Elisabeth A. , Meltzer Paul S. , Gardner Lynn M. G. , Hess Angela R. , Kirschmann Dawn A. , Schatteman Gina C. , Seftor Richard E. B.
Published: July 2002

We recently have introduced the term vasculogenic mimicry to describe the unique ability of aggressive melanoma tumor cells to form tubular structures and patterned networks in three-dimensional culture, which “mimics” embryonic vasculogenic networks formed by differentiating endothelial cells. In the current study, we address the biological significance of several endothelial-associated molecules (revealed by microarray analysis) with respect to expression and function in highly aggressive and poorly aggressive human cutaneous melanoma cell lines (established from the same patient). In a comparative analysis, CD31 was not expressed by any of the melanoma cell lines, whereas TIE-1 (tyrosine kinase with Ig and epidermal growth factor homology domains-1) was strongly expressed in the highly aggressive tumor cells with a low level of expression in one of the poorly aggressive cell lines. Vascular endothelial (VE)-cadherin was exclusively expressed by highly aggressive melanoma cells and was undetectable in the poorly aggressive tumor cells, suggesting the possibility of a vasculogenic switch. Down-regulation of VE-cadherin expression in the aggressive melanoma cells abrogated their ability to form vasculogenic networks and directly tested the hypothesis that VE-cadherin is critical in melanoma vasculogenic mimicry. These results highlight the plasticity of aggressive melanoma cells and call into question their possible genetic reversion to an embryonic phenotype. This finding could pose a significant clinical challenge in targeting tumor cells that may masquerade as circulating endothelial cells or other embryonic-like stem cells.
Genome-wide gene expression profiles of the developing mouse hippocampus
Authors: Mody Monica , Cao Yanxiang , Cui Zhenzhong , Tay Khoon-Yen , Shyong Andy , Shimizu Eiji , Pham Kelvin , Schultz Peter , Welsh Douglas , Tsien Joe Z.
Published: July 2002

We have analyzed the developmental molecular programs of the mouse hippocampus, a cortical structure critical for learning and memory, by means of large-scale DNA microarray techniques. Of 11,000 genes and expressed sequence tags examined, 1,926 showed dynamic changes during hippocampal development from embryonic day 16 to postnatal day 30. Gene-cluster analysis was used to group these genes into 16 distinct clusters with striking patterns that appear to correlate with major developmental hallmarks and cellular events. These include genes involved in neuronal proliferation, differentiation, and synapse formation. A complete list of the transcriptional changes has been compiled into a comprehensive gene profile database (
http://BrainGenomics.Princeton.edu
), which should prove valuable in advancing our understanding of the molecular and genetic programs underlying both the development and the functions of the mammalian brain.
Barrier-to-autointegration factor (BAF) bridges DNA in a discrete, higher-order nucleoprotein complex
Authors: Zheng Ronglan , Ghirlando Rodolfo , Lee Myung Soo , Mizuuchi Kiyoshi , Krause Michael , Craigie Robert
Published: July 2002

Barrier-to-autointegration factor (BAF) is a highly conserved cellular protein that was identified by its activity in protecting retroviral DNA against autointegration. We show that BAF has the property of bridging double-stranded DNA in a highly ordered nucleoprotein complex. Whereas BAF protein alone is a dimer in solution, upon binding DNA, BAF forms a dodecamer with DNA bound at multiple discrete sites in the complex. The interactions between BAF and DNA are entirely nonspecific with respect to DNA sequence. The dual interaction of BAF with DNA and LAP2, a protein associated with the nuclear lamina, suggests a role for LAP2 in chromosome organization. Consistent with this idea, RNA interference experiments with
Caenorhabditis
elegans
reveal a defect in mitosis.
A germ-line
Tsc1
mutation causes tumor development and embryonic lethality that are similar, but not identical to, those caused by
Tsc2
mutation in mice
Authors: Kobayashi Toshiyuki , Minowa Osamu , Sugitani Yoshinobu , Takai Setsuo , Mitani Hiroaki , Kobayashi Etsuko , Noda Tetsuo , Hino Okio
Published: July 2002

Tuberous sclerosis (TS) is characterized by the development of hamartomas in various organs and is caused by a germ-line mutation in either
TSC1
or
TSC2
tumor suppressor genes. From the symptomatic resemblance among TS patients, involvement of TSC1 and TSC2 products in a common pathway has been suggested. Here, to analyze the function of the Tsc1 product, we established a line of
Tsc1
(
TSC1
homologue) knockout mouse by gene targeting. Heterozygous
Tsc1
mutant (
Tsc1
+/−
) mice developed renal and extra-renal tumors such as hepatic hemangiomas. In these tumors, loss of wild-type
Tsc1
allele was observed. Homozygous
Tsc1
mutants died around embryonic days 10.5–11.5, frequently associated with neural tube unclosure. As a whole, phenotypes of
Tsc1
knockout mice resembled those of
Tsc2
knockout mice previously reported, suggesting that the presumptive common pathway for Tsc1 and Tsc2 products may also exist in mice. Notably, however, development of renal tumors in
Tsc1
+/−
mice was apparently slower than that in
Tsc2
+/−
mice. The
Tsc1
knockout mouse described here will be a useful model to elucidate the function of Tsc1 and Tsc2 products as well as pathogenesis of TS.
Regulation of myostatin activity and muscle growth
Authors: Lee Se-Jin , McPherron Alexandra C.
Published: July 2002

Myostatin is a transforming growth factor-β family member that acts as a negative regulator of skeletal muscle mass. To identify possible myostatin inhibitors that may have applications for promoting muscle growth, we investigated the regulation of myostatin signaling. Myostatin protein purified from mammalian cells consisted of a noncovalently held complex of the N-terminal propeptide and a disulfide-linked dimer of C-terminal fragments. The purified C-terminal myostatin dimer was capable of binding the activin type II receptors, Act RIIB and, to a lesser extent, Act RIIA. Binding of myostatin to Act RIIB could be inhibited by the activin-binding protein follistatin and, at higher concentrations, by the myostatin propeptide. To determine the functional significance of these interactions
in vivo
, we generated transgenic mice expressing high levels of the propeptide, follistatin, or a dominant-negative form of Act RIIB by using a skeletal muscle-specific promoter. Independent transgenic mouse lines for each construct exhibited dramatic increases in muscle mass comparable to those seen in myostatin knockout mice. Our findings suggest that the propeptide, follistatin, or other molecules that block signaling through this pathway may be useful agents for enhancing muscle growth for both human therapeutic and agricultural applications.
Htra2-β
1
stimulates an exonic splicing enhancer and can restore full-length
SMN
expression to
survival motor neuron
2 (
SMN2
)
Authors: Hofmann Yvonne , Lorson Christian L. , Stamm Stefan , Androphy Elliot J. , Wirth Brunhilde
Published: July 2002

Spinal muscular atrophy (SMA), a common motor neuron disease in humans, results from loss of functional survival motor neuron (
SMN1
) alleles. A nearly identical copy of the gene,
SMN2
, fails to provide protection from SMA because of a single translationally silent nucleotide difference in exon 7. This likely disrupts an exonic splicing enhancer and causes exon 7 skipping, leading to abundant production of a shorter isoform,
SMN2Δ
7
. The truncated transcript encodes a less stable protein with reduced self-oligomerization activity that fails to compensate for the loss of
SMN1.
This report describes the identification of an
in vivo
regulator of
SMN
mRNA processing. Htra2-β1, an SR-like splicing factor and ortholog of
Drosophila melanogaster
transformer-2, promoted the inclusion of
SMN
exon 7, which would stimulate full-length
SMN
2 expression. Htra2-β1 specifically functioned through and bound an AG-rich exonic splicing enhancer in
SMN
exon 7. This effect is not species-specific as expression of Htra2-β1 in human or mouse cells carrying an
SMN2
minigene dramatically increased production of full-length
SMN2.
This demonstrates that
SMN2
mRNA processing can be modulated
in vivo
. Because all SMA patients retain at least one
SMN2
copy, these results show that an
in vivo
modulation of
SMN
RNA processing could serve as a therapeutic strategy to prevent SMA.
Requirement for either a host- or pectin-induced pectate lyase for infection of
Pisum sativum
by
Nectria hematococca
Authors: Rogers Linda M. , Kim Yeon-Ki , Guo Wenjin , González-Candelas Luis , Li Daoxin , Kolattukudy Pappachan E.
Published: July 2002

Fungal pathogens usually have multiple genes that encode
extracellular hydrolytic enzymes that may degrade the physical barriers
in their hosts during the invasion process.
Nectria
hematococca
, a plant pathogen, has two inducible pectate lyase
(PL) genes (
pel
) encoding PL that can help degrade the
carbohydrate barrier in the host.
pel
A is induced by
pectin, whereas
pel
D is induced only
in
planta
. We show that the disruption of either the
pel
A or
pel
D genes alone causes no
detectable decrease in virulence. Disruption of both
pel
A and
pel
D drastically reduces
virulence. Complementation of the double disruptant with
pel
D gene, or supplementation of the infection droplets
of the double disruptant with either purified enzyme, PLA, or PLD,
caused a recovery in virulence. These results show that PL is a
virulence factor. Thus, we demonstrate that disruption of all
functionally redundant genes is required to demonstrate the role of
host barrier-degrading enzymes in pathogenesis and that dismissal of
the role of such enzymes based on the effects of single-gene disruption
may be premature.
Reward and punishment
Authors: Sigmund Karl , Hauert Christoph , Nowak Martin A.
Published: July 2002

Minigames capturing the essence of Public Goods experiments show that even in the absence of rationality assumptions, both punishment and reward will fail to bring about prosocial behavior. This result holds in particular for the well-known Ultimatum Game, which emerges as a special case. But reputation can induce fairness and cooperation in populations adapting through learning or imitation. Indeed, the inclusion of reputation effects in the corresponding dynamical models leads to the evolution of economically productive behavior, with agents contributing to the public good and either punishing those who do not or rewarding those who do. Reward and punishment correspond to two types of bifurcation with intriguing complementarity. The analysis suggests that reputation is essential for fostering social behavior among selfish agents, and that it is considerably more effective with punishment than with reward.
A metallothionein containing a zinc finger within a four-metal cluster protects a bacterium from zinc toxicity
Authors: Blindauer Claudia A. , Harrison Mark D. , Parkinson John A. , Robinson Andrea K. , Cavet Jennifer S. , Robinson Nigel J. , Sadler Peter J.
Published: July 2002

Zinc is essential for many cellular processes, including DNA synthesis, transcription, and translation, but excess can be toxic. A zinc-induced gene,smtA, is required for normal zinc-tolerance in the cyanobacteriumSynechococcusPCC 7942. Here we report that the protein SmtA contains a cleft lined with Cys-sulfur and His-imidazole ligands that binds four zinc ions in a Zn4Cys9His2cluster. The thiolate sulfurs of five Cys ligands provide bridges between the two ZnCys4and two ZnCys3His sites, giving two fused six-membered rings with distorted boat conformations. The inorganic core strongly resembles the Zn4Cys11cluster of mammalian metallothionein, despite different amino acid sequences, a different linear order of the ligands, and presence of histidine ligands. Also, SmtA contains elements of secondary structure not found in metallothioneins. One of the two Cys4-coordinated zinc ions in SmtA readily exchanges with exogenous metal (111Cd), whereas the other is inert. The thiolate sulfur ligands bound to zinc in this site are buried within the protein. Regions of β-strand and α-helix surround the inert site to form a zinc finger resembling the zinc fingers in GATA and LIM-domain proteins. Eukaryotic zinc fingers interact specifically with other proteins or DNA and an analogous interaction can therefore be anticipated for prokaryotic zinc fingers. SmtA now provides structural proof for the existence of zinc fingers in prokaryotes, and sequences related to the zinc finger motif can be identified in several bacterial genomes.
Does oxidative damage to DNA increase with age?
Authors: Hamilton Michelle L. , Van Remmen Holly , Drake Jessica A. , Yang Hong , Guo Zhong Mao , Kewitt Kristen , Walter Christi A. , Richardson Arlan
Published: July 2002

The levels of 8-oxo-2-deoxyguanosine (oxo8dG) in DNA isolated from tissues of rodents (male F344 rats, male B6D2F1 mice, male C57BL/6 mice, and female C57BL/6 mice) of various ages were measured using sodium iodide to prevent oxidative damage to DNA during DNA isolation. Oxo8dG was measured in nuclear DNA (nDNA) isolated from liver, heart, brain, kidney, skeletal muscle, and spleen and in mitochondrial DNA (mtDNA) isolated from liver. We observed a significant increase in oxo8dG levels in nDNA with age in all tissues and strains of rodents studied. The age-related increase in oxo8dG in nDNA from old mice was shown not to the result of the tissue's reduced ability to remove the oxo8dG lesion. Rather, the increase in oxo8dG levels appears to arise from an age-related increase in the sensitivity of these tissues to oxidative stress. We also observed an age-related increase in oxo8dG in mtDNA isolated from the livers of the rats and mice. Dietary restriction, which is known to retard aging and increase the lifespan of rodents, was shown to significantly reduce the age-related accumulation of oxo8dG levels in nDNA in all tissues of male B6D23F1 mice and in most tissues of male F344 rats. Our study also showed that dietary restriction prevented the age-related increase in oxo8dG levels in mtDNA isolated from the livers of both rats and mice.
Effects of exposure to event 176
Bacillus thuringiensis
corn pollen on monarch and black swallowtail caterpillars under field conditions
Authors: Zangerl A. R. , McKenna D. , Wraight C. L. , Carroll M. , Ficarello P. , Warner R. , Berenbaum M. R.
Published: July 2002

The widespread planting of corn genetically modified to produce
Bacillus thuringiensis
endotoxin has led to speculation that pollen from these fields might adversely affect nearby nontarget lepidopterans. A previous study of
Bt
corn engineered with Monsanto event 810 failed to detect an effect of pollen exposure on the black swallowtail,
Papilio polyxenes
, in either the field or the laboratory. Here, we report results of a field study investigating the impact of exposure to pollen from a
Bt
corn hybrid containing Novartis event 176 on two species of Lepidoptera, black swallowtails and monarch butterflies,
Danaus plexippus
. Nearly half of the 600 monarch larvae died within the first 24 h; this and subsequent mortality was not associated with proximity to
Bt
corn and may have been due in part to predation. Survivorship of black swallowtails was much higher than that of the monarchs and was also independent of proximity to the transgenic corn. However, despite five rainfall events that removed much of the pollen from the leaves of their host plants during the experiment, we observed a significant reduction in growth rates of black swallowtail larvae that was likely caused by pollen exposure. These results suggest that
Bt
corn incorporating event 176 can have adverse sublethal effects on black swallowtails in the field and underscore the importance of event selection in reducing environmental impacts of transgenic plants.
Oligodendrocyte lineage genes (
OLIG
) as molecular markers for human glial brain tumors
Authors: Lu Q. Richard , Park John K. , Noll Elizabeth , Chan Jennifer A. , Alberta John , Yuk Dongin , Alzamora M. Garcia , Louis David N. , Stiles Charles D. , Rowitch David H. , Black Peter M.
Published: July 2002

The most common primary tumors of the human brain are thought to be of glial cell origin. However, glial cell neoplasms cannot be fully classified by cellular morphology or with conventional markers for astrocytes, oligodendrocytes, or their progenitors. Recent insights into central nervous system tumorigenesis suggest that novel molecular markers might be found among factors that have roles in glial development. Oligodendrocyte lineage genes (
Olig1/2
) encode basic helix–loop–helix transcription factors. In the rodent central nervous system, they are expressed exclusively in oligodendrocytes and oligodendrocyte progenitors, and
Olig1
can promote formation of an chondroitin sulfate proteoglycon-positive glial progenitor. Here we show that human
OLIG
genes are expressed strongly in oligodendroglioma, contrasting absent or low expression in astrocytoma. Our data provide evidence that neoplastic cells of oligodendroglioma resemble oligodendrocytes or their progenitor cells and may derive from cells of this lineage. They further suggest the diagnostic potential of
OLIG
markers to augment identification of oligodendroglial tumors.
Adult-generated hippocampal and neocortical neurons in macaques have a transient existence
Authors: Gould E. , Vail N. , Wagers M. , Gross C. G.
Published: July 2002

Previously we reported that new neurons are added to the hippocampus and neocortex of adult macaque monkeys. Here we compare the production and survival of adult-generated neurons and glia in the dentate gyrus, prefrontal cortex, and inferior temporal cortex. Twelve adult macaques were injected with the thymidine analogue BrdUrd, and the phenotypes of labeled cells were examined after 2 h, 24 h, 2 wk, 5 wk, 9 wk, and 12 wk by using the following immunocytochemical markers: for immature and mature neurons, class III β-tubulin (TuJ1); for mature neurons, neuronal nuclei; for astrocytes, glial fibrillary acidic protein; and for oligodendrocytes, 2′,3′-cyclic nucleotide 3′ phosphodiesterase. We found that the dentate gyrus had many more BrdUrd-labeled cells than either neocortical area. Furthermore, a greater percentage of BrdUrd-labeled cells expressed a neuronal marker in the dentate gyrus than in either neocortical area. The number of new cells in all three areas declined by 9 wk after BrdUrd labeling, suggesting that some of the new cells have a transient existence. BrdUrd-labeled cells also were found in the subventricular zone and in the white matter between the lateral ventricle and neocortex; some of the latter cells were double-labeled for BrdUrd and TuJ1. Adult neocortical neurogenesis is not restricted to primates. Five adult rats were injected with BrdUrd, and after a 3-wk survival time, there were cells double-labeled for BrdUrd and either TuJ1 or neuronal nuclei in the anterior neocortex as well as the dentate gyrus.
Biosynthesis and insecticidal properties of plant cyclotides: The cyclic knotted proteins from
Oldenlandia affinis
Authors: Jennings Cameron , West Jenny , Waine Clement , Craik David , Anderson Marilyn
Published: July 2002

Several members of the Rubiaceae and Violaceae families produce a series of cyclotides or macrocyclic peptides of 29–31 amino acids with an embedded cystine knot. We aim to understand the mechanism of synthesis of cyclic peptides in plants and have isolated a cDNA clone that encodes the cyclotide kalata B1 as well as three other clones for related cyclotides from the African plant
Oldenlandia affinis
. The cDNA clones encode prepropeptides with a 20-aa signal sequence, an N-terminal prosequence of 46–68 amino acids and one, two, or three cyclotide domains separated by regions of about 25 aa. The corresponding cyclotides have been isolated from plant material, indicating that the cyclotide domains are excised and cyclized from all four predicted precursor proteins. The exact processing site is likely to lie on the N-terminal side of the strongly conserved GlyLeuPro or SerLeuPro sequence that flanks both sides of the cyclotide domain. Cyclotides have previously been assigned an antimicrobial function; here we describe a potent inhibitory effect on the growth and development of larvae from the Lepidopteran species
Helicoverpa punctigera.
Overlapping recognition determinants within the ssrA degradation tag allow modulation of proteolysis
Authors: Flynn Julia M. , Levchenko Igor , Seidel Meredith , Wickner Sue H. , Sauer Robert T. , Baker Tania A.
Published: July 2002

The ssrA tag, an 11-aa peptide added to the C terminus of proteins stalled during translation, targets proteins for degradation by ClpXP and ClpAP. Mutational analysis of the ssrA tag reveals independent, but overlapping determinants for its interactions with ClpX, ClpA, and SspB, a specificity-enhancing factor for ClpX. ClpX interacts with residues 9–11 at the C terminus of the tag, whereas ClpA recognizes positions 8–10 in addition to residues 1–2 at the N terminus. SspB interacts with residues 1–4 and 7, N-terminal to the ClpX-binding determinants, but overlapping the ClpA determinants. As a result, SspB and ClpX work together to recognize ssrA-tagged substrates efficiently, whereas SspB inhibits recognition of these substrates by ClpA. Thus, dissection of the recognition signals within the ssrA tag provides insight into how multiple proteins function in concert to modulate proteolysis.
Ordered upwind methods for static Hamilton–Jacobi equations
Authors: Sethian J. A. , Vladimirsky A.
Published: July 2002

We introduce a family of fast ordered upwind methods for
approximating solutions to a wide class of static Hamilton–Jacobi
equations with Dirichlet boundary conditions. Standard techniques often
rely on iteration to converge to the solution of a discretized version
of the partial differential equation. Our fast methods avoid iteration
through a careful use of information about the characteristic
directions of the underlying partial differential equation. These
techniques are of complexity
O
(
M
log
M
), where
M
is the total number of points
in the domain. We consider anisotropic test problems in optimal
control, seismology, and paths on surfaces.
Aging mechanisms
Authors: Takahashi Yoshiko , Kuro-o Makoto , Ishikawa Fuyuki
Published: July 2002

Aging (senescence) has long been a difficult issue to be
experimentally analyzed because of stochastic processes, which contrast
with the programmed events during early development. However, we have
recently started to learn the molecular mechanisms that control aging.
Studies of the mutant mouse,
klotho,
showing premature
aging, raise a possibility that mammals have an “anti-aging
hormone.” A decrease of cell proliferation ability caused by the
telomeres is also tightly linked to senescence. Frontier experimental
studies of aging at the molecular level are leading to fascinating
hypotheses that aging is the price we had to pay for the evolution of
the sexual reproduction system that produces a variety of genetic
information and complex body structures.