bluuebunny/crossref_metadata_2025 huggingface dataset:
Group B streptococci escape host immunity by deletion of tandem repeat elements of the alpha C protein.
Authors: Madoff L C , Michel J L , Gong E W , Kling D E , Kasper D L
Published: July 2002

Group B streptococci (GBS) are the most common cause of neonatal sepsis, pneumonia, and meningitis. The alpha C protein is a surface-associated antigen; the gene (bca) for this protein contains a series of tandem repeats (each encoding 82 aa) that are identical at the nucleotide level and express a protective epitope. We previously reported that GBS isolates from two of 14 human maternal and neonatal pairs differed in the number of repeats contained in their alpha C protein; in both pairs, the alpha C protein of the neonatal isolate was smaller in molecular size. We now demonstrate by PCR that the neonatal isolates contain fewer tandem repeats. Maternal isolates were susceptible to opsonophagocytic killing in the presence of alpha C protein-specific antiserum, whereas the discrepant neonatal isolates proliferated. An animal model was developed to further study this phenomenon. Adult mice passively immunized with antiserum to the alpha C protein were challenged with an alpha C protein-expressing strain of GBS. Splenic isolates of GBS from these mice showed a high frequency of mutation in bca--most commonly a decrease in repeat number. Isolates from non-immune mice were not altered. Spontaneous deletions in the repeat region were observed at a much lower frequency (6 x 10(-4)); thus, deletions in that region are selected for under specific antibody pressure and appear to lower the organism's susceptibility to killing by antibody specific to the alpha C protein. This mechanism of antigenic variation may provide a means whereby GBS evade host immunity.
Viral dynamics in hepatitis B virus infection.
Authors: Nowak M A , Bonhoeffer S , Hill A M , Boehme R , Thomas H C , McDade H
Published: July 2002

Treatment of chronic hepatitis B virus (HBV) infections with the reverse transcriptase inhibitor lamivudine leads to a rapid decline in plasma viremia and provides estimates for crucial kinetic constants of HBV replication. We find that in persistently infected patients, HBV particles are cleared from the plasma with a half-life of approximately 1.0 day, which implies a 50% daily turnover of the free virus population. Total viral release into the periphery is approximately 10(11) virus particles per day. Although we have no direct measurement of the infected cell mass, we can estimate the turnover rate of these cells in two ways: (i) by comparing the rate of viral production before and after therapy or (ii) from the decline of hepatitis B antigen during treatment. These two independent methods give equivalent results: we find a wide distribution of half-lives for virus-producing cells, ranging from 10 to 100 days in different patients, which may reflect differences in rates of lysis of infected cells by immune responses. Our analysis provides a quantitative understanding of HBV replication dynamics in vivo and has implications for the optimal timing of drug treatment and immunotherapy in chronic HBV infection. This study also represents a comparison for recent findings on the dynamics of human immunodeficiency virus (HIV) infection. The total daily production of plasma virus is, on average, higher in chronic HBV carriers than in HIV-infected patients, but the half-life of virus-producing cells is much shorter in HIV. Most strikingly, there is no indication of drug resistance in HBV-infected patients treated for up to 24 weeks.
Functional expression of a novel human neurokinin-3 receptor homolog that binds [
3
H]senktide and [
125
I-MePhe
7
]neurokinin B, and is responsive to tachykinin peptide agonists
Authors: Krause J. E. , Staveteig P. T. , Mentzer J. Nave , Schmidt S. K. , Tucker J. B. , Brodbeck R. M. , Bu J.-Y. , Karpitskiy V. V.
Published: July 2002

In 1992, Xie
et al
. identified a cDNA sequence in the expression cloning search for the κ opioid receptor. When the cDNA was expressed in Cos-7 cells, binding of opioid compounds was observed to be of low affinity and without κ, μ, or δ selectivity [Xie, G.-X., Miyajima, A. and Goldstein, A. (1992)
Proc. Natl. Acad. Sci. USA
89, 4124–4128]. This cDNA was highly homologous to the human neurokinin-3 (NK-3) receptor sequence, and displayed lower homology to NK-1 and NK-2 sequences. This sequence was stably expressed in Chinese hamster ovary cells, which do not express neurokinin receptors naturally, and ligand binding and second messenger characteristics were compared with a human NK-3 receptor. The NK-3 receptor homolog bound [
3
H]senktide with a
K
d
of 39 nM, similar to that of the NK-3 receptor. The rank order of tachykinin peptides competing for [
3
H]senktide binding at the NK-3 receptor homolog was [MePhe
7
]neurokinin B > senktide > substance P = neurokinin A > neurokinin B. This cell line also bound [
125
I-MePhe
7
]neurokinin B; however, neurokinin B was an effective competitor. Tachykinin peptides stimulated both inositol phospholipid hydrolysis and arachidonic acid release at NK-3 and NK-3 receptor homolog cell lines, with similar rank orders of potency of [MePhe
7
]neurokinin B = neurokinin B = senktide > NKA = substance P. These results indicate that expression of the NK-3 receptor homolog cDNA in the Chinese hamster ovary cell system induces the expression of a receptor site with many similarities but certain key differences from that of the human NK-3 receptor. The results are discussed with reference to the existence of a novel human tachykinin receptor.
Copper-mediated repression of the activation domain in the yeast Mac1p transcription factor
Authors: Graden Janet A. , Winge Dennis R.
Published: July 2002

The expression of a number of genes encoding products involved in copper ion uptake in yeast is specifically inhibited by copper ions. We show here that copper metalloregulation occurs through Cu-dependent repression of the transactivation activity of Mac1p. A segment of the yeast transcription factor Mac1p was identified that activated transcription
in vivo
in a heterologous system using fusion polypeptides with the yeast Gal4 DNA-binding domain. The Gal4/Mac1p hybrid exhibits transactivation activity that is repressed in cells cultured in the presence of copper salts and derepressed in cells with reduced copper uptake. The repressive effect is specific for copper ions. The concentration dependency of the Cu-inactivation of Gal4/Mac1p is similar to that of Cu-inhibition of
CTR1
expression, a known Cu-regulated gene
in vivo
. Copper inhibition of gene expression is not observed with a Gal4/Mac1p chimera containing the
MAC1

up1

substitution within the transactivation domain. Cells harboring the
MAC1

up1

allele fail to attenuate
FRE1
and
CTR1
expression in a Cu-dependent manner. Additional
MAC1

up

alleles exist within the first of two cysteine-rich sequence motifs adjacent to the His → Gln
MAC1

up1

encoded substitution. Thus, Cu-regulation of Mac1p function arises from a novel Cu-specific repression of the transactivation domain function. Models for the mechanism of Cu-repression of Mac1p function will be discussed.
Interaction of protein kinase C ζ with ZIP, a novel protein kinase C-binding protein
Authors: Puls Axel , Schmidt Sandra , Grawe Ferdi , Stabel Silvia
Published: July 2002

The atypical protein kinase C (PKC) member PKC-ζ has been implicated in several signal transduction pathways regulating differentiation, proliferation or apoptosis of mammalian cells. We report here the identification of a cytoplasmic and membrane-associated protein that we name zeta-interacting protein (ZIP) and that interacts with the regulatory domain of PKC-ζ but not classic PKCs. The structural motifs in ZIP include a recently defined ZZ zinc finger as a potential protein binding module, two PEST sequences and a novel putative protein binding motif with the consensus sequence
Y
X
DED
X
5
SDEE/D
. ZIP binds to the pseudosubstrate region in the regulatory domain of PKC-ζ and is phosphorylated by PKC-ζ
in vitro
. ZIP dimerizes via the same region that promotes binding to PKC-ζ suggesting a competitive situation between ZIP:ZIP and ZIP:PKC-ζ complexes. In the absence of PKC-ζ proper subcellular localization of ZIP is impaired and we show that intracellular targeting of ZIP is dependent on a balanced interaction with PKC-ζ. Taking into account the recent isolation of ZIP by others in different contexts we propose that ZIP may function as a scaffold protein linking PKC-ζ to protein tyrosine kinases and cytokine receptors.
Direct isolation of human
BRCA2
gene by transformation-associated recombination in yeast
Authors: Larionov Vladimir , Kouprina Natalya , Solomon Gregory , Barrett J. Carl , Resnick Michael A.
Published: July 2002

Mutant forms of the
BRCA2
gene contribute significantly to hereditary breast cancer. Isolation of the normal and mutant forms of the
BRCA2
gene with its natural promoter would greatly facilitate analysis of the gene and its contribution to breast cancer. We have accomplished the direct isolation of the 90-kb gene from total human DNA by transformation-associated recombination in yeast using a small amount of 5′ and 3′
BRCA2
sequence information. Because the entire isolation procedure of a single chromosomal gene could be accomplished in approximately 2 weeks, the transformation-associated recombination cloning approach is readily applicable to studies of chromosome alterations and human genetic diseases.
A natural polymorphism in β-lactamase is a global suppressor
Authors: Huang Wanzhi , Palzkill Timothy
Published: July 2002

A M182T substitution was discovered as a second-site suppressor of a missense mutation in TEM-1 β-lactamase. The combination of the M182T substitution with other substitutions in the enzyme indicates the M182T substitution is a global suppressor of missense mutations in β-lactamase. The M182T substitution also is found in natural variants of TEM-1 β-lactamase with altered substrate specificity that have evolved in response to antibiotic therapy. The M182T substitution may have been selected in natural isolates as a suppressor of folding or stability defects resulting from mutations associated with drug resistance. This pathway of protein evolution may occur in other targets of antimicrobial drugs such as the HIV protease.
The β subunit of CKII negatively regulates
Xenopus
oocyte maturation
Authors: Chen Mingzi , Cooper Jonathan A.
Published: July 2002

CKII (formerly known as casein kinase II) is a ubiquitously expressed enzyme that plays an important role in regulating cell growth and differentiation. The β subunit of CKII (CKIIβ) is not catalytic but forms heterotetramers with the catalytic subunit α to generate an α
2
β
2
holoenzyme. In
Xenopus
oocytes, CKIIβ also associates with another serine/threonine kinase, Mos. As a key regulator of meiosis, Mos is necessary and sufficient to initiate oocyte maturation. We have previously shown that the binding of CKIIβ to Mos represses Mos-mediated mitogen-activated protein kinase (MAPK) activation and that the ectopic expression of CKIIβ inhibits progesterone-induced
Xenopus
oocyte maturation. We have now used an antisense oligonucleotide technique to reduce the endogenous CKIIβ protein level in
Xenopus
oocytes, and we find that oocytes with a reduced content of CKIIβ are more sensitive to low doses of progesterone and show accelerated MAPK activation and germinal vesicle breakdown. Furthermore, ectopic expression of a Mos-binding fragment of CKIIβ suppressed the effect of antisense oligonucleotide. These results suggest that the endogenous CKIIβ normally sets a threshold level for Mos protein, which must be exceeded for Mos to activate the MAPK signaling pathway and induce oocyte maturation.
In vitro
repair of oxidative DNA damage by human nucleotide excision repair system: Possible explanation for neurodegeneration in Xeroderma pigmentosum patients
Authors: Reardon Joyce T. , Bessho Tadayoshi , Kung Hsiang Chuan , Bolton Philip H. , Sancar Aziz
Published: July 2002

Xeroderma pigmentosum (XP) patients fail to remove pyrimidine dimers caused by sunlight and, as a consequence, develop multiple cancers in areas exposed to light. The second most common sign, present in 20–30% of XP patients, is a set of neurological abnormalities caused by neuronal death in the central and peripheral nervous systems. Neural tissue is shielded from sunlight-induced DNA damage, so the cause of neurodegeneration in XP patients remains unexplained. In this study, we show that two major oxidative DNA lesions, 8-oxoguanine and thymine glycol, are excised from DNA
in vitro
by the same enzyme system responsible for removing pyrimidine dimers and other bulky DNA adducts. Our results suggest that XP neurological disease may be caused by defective repair of lesions that are produced in nerve cells by reactive oxygen species generated as by-products of an active oxidative metabolism.
Biochemical changes in the frontal lobe of HIV-infected individuals detected by magnetic resonance spectroscopy
Authors: López-Villegas Dolores , Lenkinski Robert E. , Frank Ian
Published: July 2002

We have developed a proton magnetic resonance spectroscopy method that selectively can sample cortical gray matter and adjacent white matter in the frontal lobe. We have used this approach to study a group of patients (
n
= 7) infected with HIV and clinical manifestations of the AIDS dementia complex (ADC), a group of patients (
n
= 8) infected with HIV without any indications of ADC, and seven controls. The patients without ADC had a statistically significant increase in the ratio of myo-inositol to creatine in white matter compared with normal controls. In contrast, the group of patients with ADC had almost normal levels of myo-inositol to creatine in both gray matter and white matter and showed a statistically significant decrease in the
N
-acetylaspartate to creatine ratio in gray matter compared with either the normal controls or the patients without ADC. Patterns of spectral abnormalities correlated with neuropsychological measures of frontal lobe dysfunction, suggesting that the evaluation of frontal lobe metabolism by magnetic resonance spectroscopy can play a role in the early detection of ADC, in determining its progression, and in assessing responses to therapeutic interventions.
The activation domain of the enhancer binding protein p45NF-E2 interacts with TAF
II
130 and mediates long-range activation of the α- and β-globin gene loci in an erythroid cell line
Authors: Amrolia Persis J. , Ramamurthy Lakshman , Saluja Daman , Tanese Naoko , Jane Stephen M. , Cunningham John M.
Published: July 2002

We have used the interaction between the erythroid-specific enhancer in hypersensitivity site 2 of the human β-globin locus control region and the globin gene promoters as a paradigm to examine the mechanisms governing promoter/enhancer interactions in this locus. We have demonstrated that enhancer-dependent activation of the globin promoters is dependent on the presence of both a TATA box in the proximal promoter and the binding site for the erythroid-specific heteromeric transcription factor NF-E2 in the enhancer. Mutational analysis of the transcriptionally active component of NF-E2, p45NF-E2, localizes the critical region for this function to a proline-rich transcriptional activation domain in the NH
2
-terminal 80 amino acids of the protein. In contrast to the wild-type protein, expression of p45 NF-E2 lacking this activation domain in an NF-E2 null cell line fails to support enhancer-dependent transcription in transient assays. More significantly, the mutated protein also fails to reactivate expression of the endogenous β- or α-globin loci in this cell line. Protein-protein interaction studies reveal that this domain of p45 NF-E2 binds specifically to a component of the transcription initiation complex, TATA binding protein associated factor TAF
II
130. These findings suggest one potential mechanism for direct recruitment of distal regulatory regions of the globin loci to the individual promoters.
Drosophila
TFIIE: Purification, cloning, and functional reconstitution
Authors: Wang Xia , Hansen Stig K. , Ratts Ryan , Zhou Sharleen , Snook Amy J. , Zehring William
Published: July 2002

We present a physical and molecular genetic characterization of
Drosophila melanogaster
TFIIE (dTFIIE), a component of the basal RNA polymerase II transcription apparatus. We have purified dTFIIE to near homogeneity from nuclear extracts of
Drosophila
embryos and found that it is composed of two subunits with apparent molecular weights of 55 and 38 kDa. Peptide sequence information derived from the two subunits was used to isolate the corresponding cDNA clones, revealing that dTFIIE and human TFIIE share extensive amino acid similarity. Functional conservation was demonstrated by the ability of bacterially expressed dTFIIE to substitute for human TFIIE in an
in vitro
transcription assay reconstituted from purified components. Cytological mapping analysis shows that both subunits are encoded by single copy genes located on chromosome III.
Identification of protein coding regions in the human genome by quadratic discriminant analysis
Authors: Zhang M. Q.
Published: July 2002

A new method for predicting internal coding exons in genomic DNA sequences has been developed. This method is based on a prediction algorithm that uses the quadratic discriminant function for multivariate statistical pattern recognition. Substantial improvements have been made (with only 9 discriminant variables) when compared with existing methods:
hexon
[Solovyev, V. V., Salamov, A. A. & Lawrence, C. B. (1994)
Nucleic Acids Res.
22, 5156–5163] (based on linear discriminant analysis) and
grail
2 [Uberbacher, E. C. & Mural, R. J. (1991)
Proc. Natl. Acad. Sci. USA
88, 11261–11265] (based on neural networks). A computer program called
mzef
is freely available to the genome community and allows users to adjust prior probability and to output alternative overlapping exons.
Corepressor SMRT binds the BTB/POZ repressing domain of the LAZ3/BCL6 oncoprotein
Authors: Dhordain Philippe , Albagli Olivier , Lin Richard J. , Ansieau Stéphane , Quief Sabine , Leutz Achim , Kerckaert Jean-Pierre , Evans Ronald M. , Leprince Dominique
Published: July 2002

TheLAZ3/BCL6(lymphoma-associated zinc finger 3/B cell lymphomas 6) gene frequently is altered in non-Hodgkin lymphomas. It encodes a sequence-specific DNA binding transcriptional repressor that contains a conserved N-terminal domain, termed BTB/POZ (bric-à-brac tramtrack broad complex/pox viruses and zinc fingers). Using a yeast two-hybrid screen, we show here that the LAZ3/BCL6 BTB/POZ domain interacts with the SMRT (silencing mediator of retinoid and thyroid receptor) protein. SMRT originally was identified as a corepressor of unliganded retinoic acid and thyroid receptors and forms a repressive complex with a mammalian homolog of the yeast transcriptional repressor SIN3 and the HDAC-1 histone deacetylase. Protein binding assays demonstrate that the LAZ3/BCL6 BTB/POZ domain directly interacts with SMRTin vitro. Furthermore, DNA-bound LAZ3/BCL6 recruits SMRTin vivo, and both overexpressed proteins completely colocalize in nuclear dots. Finally, overexpression of SMRT enhances the LAZ3/BCL6-mediated repression. These results define SMRT as a corepressor of LAZ3/BCL6 and suggest that LAZ3/BCL6 and nuclear hormone receptors repress transcription through shared mechanisms involving SMRT recruitment and histone deacetylation.
Deforming semistable Galois representations
Authors: Fontaine Jean-Marc
Published: July 2002

Let
V
be a
p
-adic representation of
Gal
(Q̄/Q). One of the ideas of Wiles’s
proof of FLT is that, if
V
is the representation associated
to a suitable autromorphic form (a modular form in his case) and if
V
′ is another
p
-adic representation of
Gal
(Q̄/Q) “closed enough” to
V
,
then
V′
is also associated to an automorphic form. In this
paper we discuss which kind of local condition at
p
one
should require on
V
and
V
′ in order to be able
to extend this part of Wiles’s methods.
Midgut-specific immune molecules are produced by the blood-sucking insect
Stomoxys calcitrans
Authors: Lehane Michael J. , Wu Dan , Lehane Stella M.
Published: July 2002

We have cloned and sequenced two defensins, Smd1 and Smd2, from anterior midgut tissue of the blood-sucking fly
Stomoxys calcitrans
. The DNA and N-terminal protein sequences suggest both are produced as prepropeptides. Smd1 differs from the classic defensin pattern in having an unusual six-amino acid-long N-terminal sequence. Both Smd1 and Smd2 have lower pI points and charge than insect defensins derived from fat body/hemocytes. Northern analysis shows both of these defensin molecules are tissue specific; both are produced by the anterior midgut tissue and, unlike the other insect defensins reported to date, neither appears to be expressed in fat body or hemocytes. Northern analysis also shows that mRNAs for both defensins are constitutively produced in the anterior midgut tissues and that these transcripts are up-regulated in response to sterile as well as a lipopolysaccharide-containing blood meal. However, anti-Gram-negative biological activity in the midgut is substantially enhanced by lipopolysaccharide. These findings suggest that the insect midgut has its own tissue-specific immune mechanisms and that this invertebrate epithelium is, like several vertebrate epithelia, protected by specific antibacterial peptides.
Identification and characterization of a conserved family of protein serine/threonine phosphatases homologous to
Drosophila
retinal degeneration C (rdgC)
Authors: Sherman Patti M. , Sun Hui , Macke Jennifer P. , Williams John , Smallwood Philip M. , Nathans Jeremy
Published: July 2002

The
Drosophila retinal degeneration C
(
rdgC
) gene encodes an unusual protein
serine/threonine phosphatase in that it contains at least two EF-hand
motifs at its carboxy terminus. By a combination of large-scale
sequencing of human retina cDNA clones and searches of expressed
sequence tag and genomic DNA databases, we have identified two
sequences in mammals [
Protein Phosphatase with
EF-hands-1
and
2
(
PPEF-1
and
PPEF-2
)] and one in
Caenorhabditis elegans
(
PPEF
) that closely resemble
rdgC
. In the
adult,
PPEF-2
is expressed specifically in retinal rod
photoreceptors and the pineal. In the retina, several isoforms of
PPEF-2 are predicted to arise from differential splicing. The isoform
that most closely resembles rdgC is localized to rod inner segments.
Together with the recently described localization of
PPEF-1
transcripts to primary somatosensory neurons and
inner ear cells in the developing mouse, these data suggest that the
PPEF family of protein serine/threonine phosphatases plays a specific
and conserved role in diverse sensory neurons.
Multipotent neural precursors can differentiate toward replacement of neurons undergoing targeted apoptotic degeneration in adult mouse neocortex
Authors: Snyder Evan Y. , Yoon Cliff , Flax Jonathan D. , Macklis Jeffrey D.
Published: July 2002

Neurons undergoing targeted photolytic cell death degenerate by apoptosis. Clonal, multipotent neural precursor cells were transplanted into regions of adult mouse neocortex undergoing selective degeneration of layer II/III pyramidal neurons via targeted photolysis. These precursors integrated into the regions of selective neuronal death; 15 ± 7% differentiated into neurons with many characteristics of the degenerated pyramidal neurons. They extended axons and dendrites and established afferent synaptic contacts. In intact and kainic acid-lesioned control adult neocortex, transplanted precursors differentiated exclusively into glia. These results suggest that the microenvironmental alterations produced by this synchronous apoptotic neuronal degeneration in adult neocortex induced multipotent neural precursors to undergo neuronal differentiation which ordinarily occurs only during embryonic corticogenesis. Studying the effects of this defined microenvironmental perturbation on the differentiation of clonal neural precursors may facilitate identification of factors involved in commitment and differentiation during normal development. Because photolytic degeneration simulates some mechanisms underlying apoptotic neurodegenerative diseases, these results also suggest the possibility of neural precursor transplantation as a potential cell replacement or molecular support therapy for some diseases of neocortex, even in the adult.
Loss of ovarian function promotes angiogenesis in human ovarian carcinoma
Authors: Schiffenbauer Yael S. , Abramovitch Rinat , Meir Gila , Nevo Nava , Holzinger Michael , Itin Ahuva , Keshet Eli , Neeman Michal
Published: July 2002

We show here that elevated levels of gonadotropins (luteinizing hormone and follicle stimulating hormone), as found in menopause or after ovariectomy, promote growth of human ovarian carcinoma by induction of tumor angiogenesis. Human epithelial ovarian cancer tumors progressed faster in ovariectomized mice. This induced growth could be attributed to the elevated levels of gonadotropins associated with loss of ovarian function because direct administration of gonadotropins also was effective in promoting tumor progression
in vivo
. On the other hand, gonadotropins had no direct effect on the proliferation of human ovarian cancer cells
in vitro
. Using MRI, we demonstrated that ovariectomy significantly (
P
< 0.02) induces neovascularization of human ovarian carcinoma spheroids implanted in nude mice. Moreover, conditioned medium of gonadotropin-treated human ovarian carcinoma cells showed increased mitogenic activity to bovine endothelial cells, and this activity could be blocked by neutralizing antibodies against luteinizing hormone and against vascular endothelial growth factor. Accordingly, gonadotropin stimulation resulted in a dose-dependent-induced expression of vascular endothelial growth factor in monolayer culture as well as in the outer proliferating cells of human ovarian cancer spheroids. These results demonstrate the significance of the elevated levels of gonadotropins, as found in menopause and in all ovarian cancer patients, on the progression of ovarian cancer and could explain the protective effect of estrogen replacement therapy. Based on these results, we suggest that hormonal therapy aimed at lowering the circulating levels of gonadotropins may possibly prolong remission in ovarian cancer by extending tumor dormancy.
Marked decrease of neuropeptide Y Y2 receptor binding sites in the hippocampus in murine prion disease
Authors: Diez Margarita , Koistinaho Jari , Dearmond Stephen J. , Groth Darlene , Prusiner Stanley B. , Hökfelt Tomas
Published: July 2002

Using autoradiographic binding methodology with monoiodinated peptide YY together with the agonists neuropeptide Y (NPY) and NPY (13–36), as well as
in situ
hybridization with oligonucleotide probes complementary to the NPY Y2 receptor (Y2-R) mRNA, we have studied whether or not intracerebral prion inoculation affects Y2-Rs in male CD-1 mice. Monoiodinated peptide YY binding, mainly representing Y2-Rs, was down-regulated by 85% in the CA1 strata oriens and radiatum and by 50–65% in the CA3 stratum oriens 110–140 days postinoculation. In the CA3 stratum radiatum, where the mossy fibers from the dentate granule cells project, there was a significant decrease in PYY binding at 110–120 days. Y2-R mRNA, moderately expressed both in the CA1 and CA3 pyramidal cell layers and the granule cell layer in the dentate gyrus, showed a slight, but not significant, decrease in CA3 neurons 130 days postinoculation. The results indicate that the accumulation of the scrapie prion protein in the CA1–3 region strongly inhibits NPY binding at the Y2-Rs, which, however, is only marginally due to reduced Y2-R mRNA expression. The loss of the ability of NPY to bind to inhibitory Y2-Rs may cause dysfunction of hippocampal circuits and may contribute to the clinical symptoms in mouse scrapie.
Regulation of dorsal fate in the neuraxis by Wnt-1 and Wnt-3a
Authors: Saint-Jeannet Jean-Pierre , He Xi , Varmus Harold E. , Dawid Igor B.
Published: July 2002

Members of the Wnt family of signaling molecules are expressed differentially along the dorsal–ventral axis of the developing neural tube. Thus we asked whether Wnt factors are involved in patterning of the nervous system along this axis. We show that Wnt-1 and Wnt-3a, both of which are expressed in the dorsal portion of the neural tube, could synergize with the neural inducers noggin and chordin in
Xenopus
animal explants to generate the most dorsal neural structure, the neural crest, as determined by the expression of
Krox-20
,
AP-2
, and
slug
. Overexpression of Wnt-1 or Wnt-3a in the neuroectoderm of whole embryos led to a dramatic increase of slug and
Krox-20
-expressing cells, but the hindbrain expression of
Krox-20
remained unaffected. Enlargement in the neural crest population could occur even when cell proliferation was inhibited. Wnt-5A and Wnt-8, neither of which is expressed in the dorsal neuroectoderm, failed to induce neural crest markers. Overexpression of glycogen synthase kinase 3, known to antagonize Wnt signaling, blocked the neural-crest-inducing activity of Wnt-3a in animal explants and inhibited neural crest formation in whole embryos. We suggest that Wnt-1 and Wnt-3a have a role in patterning the neural tube along its dorsoventral axis and function in the differentiation of the neural crest.
Anin vitrostudy of the dynamic features of the major histocompatibility complex class I complex relevant to its role as a versatile peptide-receptive molecule
Authors: Hörig Heidi , Papadopoulos Nicholas J. , Vegh Zsuzsanna , Palmieri Edith , Angeletti Ruth H. , Nathenson Stanley G.
Published: July 2002

The major histocompatibility complex class I complex consists of a heavy chain and a light chain (β2-microglobulin, β2m), which assemble with a short endogenously derived peptide in the endoplasmic reticulum. The class I peptide can be directly exchanged, either at the cell surface or, as recently described, in vesicles of the endocytic compartments, thus allowing exogenous peptides to enter the class I presentation pathway. To probe the interactions between the components of the class I molecule, we analyzed the exchange of peptide and β2m by using purified, recombinant H2-Kb/peptide complexes in a cell-freein vitrosystem. The exchange of competitor peptide was primarily dependent on the off-rate of the original peptide in the class I binding groove. Peptide exchange was not enhanced by the presence of exogenous β2m, as exchange occurred to the same extent in its absence. Thus, the exchange of peptide and β2m are independent events. The exchange rate of β2m also was not affected by the dissociation rates of the original peptides. Furthermore, peptides could substantially exchange into class I molecules over a pH range of 5.5 to 7.5, conditions prevalent in certain endocytic compartments. We conclude that the dynamic properties of the components of class I molecules explain its function as a highly peptide-receptive molecule. The major histocompatibility complex class I can readily receive peptides independent of the presence of exogenous β2m, even at a low pH. Such properties are relevant to class I peptide acquisition, which can occur at the cell surface, as well as in specialized endosomes.
Drosophila
host defense: Differential induction of antimicrobial peptide genes after infection by various classes of microorganisms
Authors: Lemaitre Bruno , Reichhart Jean-Marc , Hoffmann Jules A.
Published: July 2002

Insects respond to microbial infection by the rapid and transient expression of several genes encoding potent antimicrobial peptides. Herein we demonstrate that this antimicrobial response of
Drosophila
is not aspecific but can discriminate between various classes of microorganisms. We first observe that the genes encoding antibacterial and antifungal peptides are differentially expressed after injection of distinct microorganisms. More strikingly,
Drosophila
that are naturally infected by entomopathogenic fungi exhibit an adapted response by producing only peptides with antifungal activities. This response is mediated through the selective activation of the Toll pathway.
A system for mutation measurement in mammalian cells: Application to γ-irradiation
Authors: Puck Theodore T. , Johnson Robert , Rasumussen Steen
Published: July 2002

Monitoring of mutagenesis by environmental agents for the purpose of preventing genetic disease including cancer must include quantitation of cell killing, sensitive measurement of mutation production by appropriate doses of each agent, and assessment of mutation repair effects in mammalian cells. A four-step procedure, in the presence and absence of a repair suppressor, is proposed: (
i
) determination of the survival curve; (
ii
) measurement of the mitotic index in cells collected after treatment with colcemid; (
iii
) construction of a mutagenesis yield curve in the presence and absence of a repair suppressor, like caffeine; and (
iv
) assessment of the effect of test agents on the repair of mutations produced by other mutagens. The procedure is quantitative, reproducible, and reasonably rapid. It involves measurement of mutations causing visible chromosomal aberrations. Numerical parameters are proposed defining quantitatively mutation, cell killing, and mutation repair capacity. The procedure is applied to γ-irradiation and can detect the effects of doses as low as 2–5 cGy. Theoretical analysis of the underlying processes is presented, using the concept of
D

E

0
, the effective dose of mutagen after repair mechanisms and neutralizing agents have acted. Microscopically visible chromosome aberrations are due to mutations that distort the process of mitotic chromosome condensation, with or without actual chromosome breakage.
The HIV coreceptors CXCR4 and CCR5 are differentially expressed and regulated on human T lymphocytes
Authors: Bleul Conrad C. , Wu Lijun , Hoxie James A. , Springer Timothy A. , Mackay Charles R.
Published: July 2002

The chemokine receptors CXCR4 and CCR5 function as coreceptors for HIV-1 entry into CD4+cells. During the early stages of HIV infection, viral isolates tend to use CCR5 for viral entry, while later isolates tend to use CXCR4. The pattern of expression of these chemokine receptors on T cell subsets and their regulation has important implications for AIDS pathogenesis and lymphocyte recirculation. A mAb to CXCR4, 12G5, showed partial inhibition of chemotaxis and calcium influx induced by SDF-1, the natural ligand of CXCR4. 12G5 stained predominantly the naive, unactivated CD26lowCD45RA+CD45R0−T lymphocyte subset of peripheral blood lymphocytes. In contrast, a mAb specific for CCR5, 5C7, stained CD26highCD45RAlowCD45R0+T lymphocytes, a subset thought to represent previously activated/memory cells. CXCR4 expression was rapidly up-regulated on peripheral blood mononuclear cells during phytohemagglutinin stimulation and interleukin 2 priming, and responsiveness to SDF-1 increased simultaneously. CCR5 expression, however, showed only a gradual increase over 12 days of culture with interleukin 2, while T cell activation with phytohemagglutinin was ineffective. Taken together, the data suggest distinct functions for the two receptors and their ligands in the migration of lymphocyte subsets through lymphoid and nonlymphoid tissues. Furthermore, the largely reciprocal expression of CXCR4 and CCR5 among peripheral blood T cells implies distinct susceptibility of T cell subsets to viral entry by T cell line-tropic versus macrophage-tropic strains during the course of HIV infection.
Induction by agrin of ectopic and functional postsynaptic-like membrane in innervated muscle
Authors: Jones G. , Meier T. , Lichtsteiner M. , Witzemann V. , Sakmann B. , Brenner H. R.
Published: July 2002

Two factors secreted from the nerve terminal, agrin and neuregulin, have been postulated to induce localization of the acetylcholine receptors (AChRs) to the subsynaptic membrane in skeletal muscle fibers. The principal function ascribed to neuregulin is induction of AChR subunit gene expression and to agrin is the aggregation of AChRs. Here we report that when myoblasts engineered to secrete an agrin fragment were placed into the nerve-free region of denervated rodent muscle, the host muscle fibers expressed AChR ɛ-subunit gene transcripts, characteristic of the neuromuscular synapse in adult muscle. Transcripts were colocalized with agrin deposits and AChR clusters that were resistant to electrical muscle activity. More directly, single innervated muscle fibers injected intracellularly with agrin expression plasmids in their extrasynaptic region developed a functional ectopic postsynaptic membrane with clusters of adult-type AChR channels and acetylcholinesterase and accumulation of myonuclei. The results demonstrate that agrin is the principal neural signal that induces the formation of the subsynaptic apparatus in the muscle fiber and controls locally, either indirectly or directly, the transcription of AChR subunit genes and the aggregation of AChRs.
Consistent loss of functional transforming growth factor β receptor expression in murine plasmacytomas
Authors: Amoroso Stephanie R. , Huang Naihui , Roberts Anita B. , Potter Michael , Letterio John J.
Published: July 2002

Murine plasmacytomas are tumors of Ig-secreting plasma cells that can be induced in genetically susceptible BALB/c mice. The deregulation of the c-mycprotooncogene is a critical oncogenic event in the development of plasmacytomas (PCTs) although it is not sufficient for their malignant transformation. We have demonstrated that PCTs produce active transforming growth factor β (TGF-β)in vitro.Because TGF-β is a potent negative regulator of the proliferation and differentiation of B lymphocytes, we examined its role in plasmacytomagenesis by comparing responsiveness to TGF-β of nonneoplastic plasma cells and PCTs. The nontransformed plasma cells that accumulate in interleukin 6 transgenic mice undergo accelerated apoptosis upon treatment with TGF-β, but the 15 PCTs studied, including primary and transplanted tumors as well as established cell lines, were refractory to TGF-β-mediated growth inhibition and apoptosis. Although PCTs lack functional TGF-β receptors as demonstrated by chemical crosslinking to radiolabeled TGF-β1, they nonetheless contain mRNA and protein for both type I and II TGF-β receptors, suggesting a potential defect in receptor trafficking or processing. The results clearly show the consistent inactivation of TGF-β receptors in plasmacytoma cells, demonstrating for the first time that interruption of a tumor suppressor pathway contributes to plasmacytomagenesis.
The nature of the excited state of the reaction center of photosystem II of green plants: A high-resolution fluorescence spectroscopy study
Authors: Peterman Erwin J. G. , van Amerongen Herbert , van Grondelle Rienk , Dekker Jan P.
Published: July 2002

We studied the electronically excited state of the isolated reaction center of photosystem II with high-resolution fluorescence spectroscopy at 5 K and compared the obtained spectral features with those obtained earlier for the primary electron donor. The results show that there is a striking resemblance between the emitting and charge-separating states in the photosystem II reaction center, such as a very similar shape of the phonon wing with characteristic features at 19 and 80 cm−1, almost identical frequencies of a number of vibrational modes, a very similar double-Gaussian shape of the inhomogeneous distribution function, and relatively strong electron-phonon coupling for both states. We suggest that the emission at 5 K originates either from an exciton state delocalized over the inactive branch of the photosystem or from a fraction of the primary electron donor that is long-lived at 5 K. The latter possibility can be explained by a distribution of the free energy difference of the primary charge separation reaction around zero. Both possibilities are in line with the idea that the state that drives primary charge separation in the reaction center of photosystem II is a collective state, with contributions from all chlorophyll molecules in the central part of the complex.
The universal ancestor
Authors: Woese Carl
Published: July 2002

A genetic annealing model for the universal ancestor of all extant life is presented; the name of the model derives from its resemblance to physical annealing. The scenario pictured starts when “genetic temperatures” were very high, cellular entities (progenotes) were very simple, and information processing systems were inaccurate. Initially, both mutation rate and lateral gene transfer levels were elevated. The latter was pandemic and pervasive to the extent that it, not vertical inheritance, defined the evolutionary dynamic. As increasingly complex and precise biological structures and processes evolved, both the mutation rate and the scope and level of lateral gene transfer, i.e., evolutionary temperature, dropped, and the evolutionary dynamic gradually became that characteristic of modern cells. The various subsystems of the cell “crystallized,” i.e., became refractory to lateral gene transfer, at different stages of “cooling,” with the translation apparatus probably crystallizing first. Organismal lineages, and so organisms as we know them, did not exist at these early stages. The universal phylogenetic tree, therefore, is not an organismal tree at its base but gradually becomes one as its peripheral branchings emerge. The universal ancestor is not a discrete entity. It is, rather, a diverse community of cells that survives and evolves as a biological unit. This communal ancestor has a physical history but not a genealogical one. Over time, this ancestor refined into a smaller number of increasingly complex cell types with the ancestors of the three primary groupings of organisms arising as a result.
Oceanic protection of prebiotic organic compounds from UV radiation
Authors: Cleaves H. James , Miller Stanley L.
Published: July 2002

It is frequently stated that UV light would cause massive destruction of prebiotic organic compounds because of the absence of an ozone layer. The elevated UV flux of the early sun compounds this problem. This applies to organic compounds of both terrestrial and extraterrestrial origin. Attempts to deal with this problem generally involve atmospheric absorbers. We show here that prebiotic organic polymers as well as several inorganic compounds are sufficient to protect oceanic organic molecules from UV degradation. This aqueous protection is in addition to any atmospheric UV absorbers and should be a ubiquitous planetary phenomenon serving to increase the size of planetary habitable zones.
Tropomyosin implicated in host protective responses to microfilariae in onchocerciasis
Authors: Jenkins Rosalind E. , Taylor Mark J. , Gilvary Nichola J. , Bianco Albert E.
Published: July 2002

A cDNA from adult femaleOnchocerca volvulusencoding the C-terminal portion of a tropomyosin isoform (termed MOv-14) has been shown previously to confer protective immunity in rodent models of onchocerciasis. The full-length sequence (designatedOv-tmy-1) obtained by PCR amplification, codes for a protein of 33 kDa and shares 91% identity with tropomyosins from other nematodes, falling to 57% identity with human α-tropomyosin.Ov-TMY-1 migrates with an apparent molecular mass of 42 kDa on SDS/PAGE and is present in all life-cycle stages, as determined by immunoblotting. Immunogold electron microscopy identified antigenic sites within muscle blocks and the cuticle of microfilariae and infective larvae. Anti-MOv14 antibodies were abundant in mice exhibiting serum-transferable protection against microfilariae conferred by vaccination with a PBS-soluble parasite extract. In contrast, little or no MOv14-specific antibody was present in mice inoculated with live microfilariae, in which resistance is mediated by antibody-independent mechanisms. In human infections, there was an inverse correlation between anti-tropomyosin IgG levels and densities of microfilariae in the skin. Seropositivity varied with the relative endemicity of infection. An immunodominant B cell epitope withinOv-TMY-1 (AQLLAEEADRKYD) was mapped to the N terminus of the MOv14 protein by using sera from protectively vaccinated mice. Intriguingly, the sequence coincides with an IgE-binding epitope within shrimp tropomyosin, believed to be responsible for hypersensitivity in individuals exhibiting allergy to shellfish. IgG and IgE antibodies reacting with theO. volvulusepitope were detected in human infections. It is concluded that antibody responses to tropomyosin may be important in limiting microfilarial densities in a proportion of individuals with onchocerciasis and have the potential to mediate hypersensitivity reactions to dead microfilariae, raising the possibility of a link with the immunopathology of infection.
Phosphatidylcholine-specific phospholipase C regulates glutamate-induced nerve cell death
Authors: Li Yonghong , Maher Pamela , Schubert David
Published: July 2002

Phosphatidylcholine-specific phospholipase C (PC-PLC) is a necessary intermediate in transducing apoptotic signals for tumor necrosis factor and Fas/Apo-1 ligands in nonneuronal cells. The data presented here show that PC-PLC also is required in oxidative glutamate-induced programmed cell death of both immature cortical neurons and a hippocampal nerve cell line, HT22. In oxidative glutamate toxicity, which is distinct from excitotoxicity, glutamate interferes with cystine uptake by blocking the cystine/glutamate antiporter, indirectly causing a depletion of intracellular glutathione. A PC-PLC inhibitor blocks oxidative glutamate toxicity, and exogenous PC-PLC potentiates glutamate toxicity. The inhibition of PC-PLC uncouples the cystine uptake from glutamate inhibition, allowing the maintenance of glutathione synthesis and cell viability. These data suggest that PC-PLC modulates neuronal cell death through a mechanism that is distinct from that involved in nonneuronal apoptosis.
The tyrosine kinase regulator Cbl enhances the ubiquitination and degradation of the platelet-derived growth factor receptor α
Authors: Miyake Sachiko , Lupher Mark L. , Druker Brian , Band Hamid
Published: July 2002

The Cbl protooncogene product has emerged as a negative regulator of receptor and nonreceptor tyrosine kinases. We recently demonstrated that oncogenic Cbl mutants upregulate the endogenous tyrosine kinase signaling machinery when expressed in the NIH 3T3 cells, and identified the platelet-derived growth factor receptor-α (PDGFRα) as one of the tyrosine kinases targeted by these oncogenes. These findings suggested a role for the normal Cbl protein in negative regulation of the PDGFRα. However, the mechanism of such negative regulation remained to be determined. Here we show that overexpression of the wild-type Cbl enhances the ligand-induced ubiquitination of the PDGFRα. Concomitantly, the PDGFRα in Cbl-overexpressing cells undergoes a faster ligand-induced degradation compared with that in the control cells. These results identify a role for Cbl in the regulation of ligand-induced ubiquitination and degradation of receptor tyrosine kinases and suggest one potential mechanism for evolutionarily conserved negative regulatory influence of Cbl on tyrosine kinases.