bluuebunny/crossref_metadata_2025 huggingface dataset:
Gene Transfer and Molecular Cloning of the Human NGF Receptor
Authors: Chao Moses V. , Bothwell Mark A. , Ross Alonzo H. , Koprowski Hilary , Lanahan Anthony A. , Buck C. Randall , Sehgal Amita
Published: October 2006

Nerve growth factor (NGF) and its receptor are important in the development of cells derived from the neural crest. Mouse L cell transformants have been generated that stably express the human NGF receptor gene transfer with total human DNA. Affinity cross-linking, metabolic labeling and immunoprecipitation, and equilibrium binding with
125
I-labeled NGF revealed that this NGF receptor had the same size and binding characteristics as the receptor from human melanoma cells and rat PC12 cells. The sequences encoding the NGF receptor were molecularly cloned using the human Alu repetitive sequence as a probe. A cosmid clone that contained the human NGF receptor gene allowed efficient transfection and expression of the receptor.
Protection of Cattle Against Foot-and-Mouth Disease by a Synthetic Peptide
Authors: DiMarchi Richard , Brooke Gerald , Gale Charles , Cracknell Victor , Doel Timothy , Mowat Noel
Published: October 2006

A chemically synthesized peptide consisting essentially of two separate regions (residues 141 to 158 and 200 to 213) of a virus coat protein (VP1) from the 0
1
Kaufbeuren strain of foot-and-mouth disease virus was prepared free of any carrier protein. It elicited high levels of neutralizing antibody and protected cattle against intradermolingual challenge by inoculation with infectious virus. Comparative evaluation of this peptide with a single-site peptide (residues 141 to 158) in guinea pigs suggests the importance of the VP1 carboxyl terminal residues in enhancing the protective response.
Associative Induction of Posttetanic and Long-Term Potentiation in CA1 Neurons of Rat Hippocampus
Authors: Sastry B. R. , Goh J. W. , Auyeung A.
Published: October 2006

Electrical stimulation of fibers in the stratum radiatum causes an excitatory postsynaptic potential in CA1 neurons of the hippocampus. Other excitatory inputs to or direct depolarization of these CA1 neurons during stimulation of the stratum radiatum caused a subsequent increase in the excitatory postsynaptic potential. This enhancement was characterized as a brief potentiation (2 to 3 minutes, similar to posttetanic potentiation) and a long-term potentiation (presumed to be involved in learning and memory). These potentiations are probably induced by an interaction of the postsynaptic cell or other presynaptic terminals with the test presynaptic terminals.
Distinct Pathways of Viral Spread in the Host Determined by Reovirus S1 Gene Segment
Authors: Tyler Kenneth L. , McPhee Dale A. , Fields Bernard N.
Published: October 2006

The genetic and molecular mechanisms that determine the capacity of a virus to utilize distinct pathways of spread in an infected host were examined by using reoviruses. Both reovirus type 1 and reovirus type 3 spread to the spinal cord following inoculation into the hindlimb or forelimb footpad of newborn mice. For type 3 this spread is through nerves and occurs via the microtubule-associated system of fast axonal transport. By contrast, type 1 spreads to the spinal cord through the bloodstream. With the use of reassortant viruses containing various combinations of double-stranded RNA segments (genes) derived from type 1 and type 3, the viral S1 double-stranded RNA segment was shown to be responsible for determining the capacity of reoviruses to spread to the central nervous system through these distinct pathways.
Oncogenesis of the Lens in Transgenic Mice
Authors: Mahon Kathleen A. , Chepelinsky Ana B. , Khillan Jaspal S. , Overbeek Paul A. , Piatigorsky Joram , Westphal Heiner
Published: October 2006

Neoplastic tumors of the ocular lens of vertebrates do not naturally occur. Transgenic mice carrying a hybrid gene comprising the murine αA-crystallin promoter (-366 to +46) fused to the coding sequence of the SV40 T antigens developed lens tumors, which obliterated the eye cavity and even invaded neighboring tissue, thus establishing that the lens is not refractive to oncogenesis. Large-T antigen was detected early in lens development; it elicited morphological changes and specifically interfered with differentiation of lens fiber cells. Both α- and β-crystallins persisted in many of the lens tumor cells, while γ-crystallin was selectively reduced. Accessibility, characteristic morphology, and defined protein markers make this transparent epithelial eye tissue a potentially useful system for testing tumorigenicity of oncogenes and for studying malignant transformation from its inception until death of the animal.
Atomic Structure of Thymidylate Synthase: Target for Rational Drug Design
Authors: Hardy Larry W. , Finer-Moore Janet S. , Montfort William R. , Jones Melvin O. , Santi Daniel V. , Stroud Robert M.
Published: October 2006

The atomic structure of thymidylate synthase from
Lactobacillus casei
was determined at 3 angstrom resolution. The native enzyme is a dimer of identical subunits. The dimer interface is formed by an unusual association between five-stranded β sheets present in each monomer. Comparison of known sequences with the
Lactobacillus casei
structure suggests that they all have a common core structure around which loops are inserted or deleted in different sequences. Residues from both subunits contribute to each active site. Two arginine side chains can contribute to binding phosphate on the substrate. The side chains of several conserved amino acids can account for other determinants of substrate binding.
MyoD1: A Nuclear Phosphoprotein Requiring a Myc Homology Region to Convert Fibroblasts to Myoblasts
Authors: Tapscott Stephen J. , Davis Robert L. , Thayer Mathew J. , Cheng Pei-Feng , Weintraub Harold , Lassar Andrew B.
Published: October 2006

Expression of a complementary DNA (cDNA) encoding the mouse MyoD1 protein in a variety of fibroblast and adipoblast cell lines converts them to myogenic cells. Polyclonal antisera to fusion proteins containing the MyoD1 sequence show that MyoD1 is a phosphoprotein present in the nuclei of proliferating myoblasts and differentiated myotubes but not expressed in 10T1/2 fibroblasts or other nonmuscle cell types. Functional domains of the MyoD1 protein were analyzed by site-directed deletional mutagenesis of the MyoD1 cDNA. Deletion of a highly basic region (residues 102 to 135) interferes with both nuclear localization and induction of myogenesis. Deletion of a short region (residues 143 to 162) that is similar to a conserved region in the c-Myc family of proteins eliminates the ability of the MyoD1 protein to initiate myogenesis but does not alter nuclear localization. Deletions of regions spanning the remainder of MyoD1 did not affect nuclear localization and did not inhibit myogenesis. Furthermore, expression of only 68 amino acids of MyoD1, containing the basic and the Myc similarity domains, is sufficient to activate myogenesis in stably transfected 10T1/2 cells. Genetic analysis maps the MyoD1 gene to mouse chromosome 7 and human chromosome 11.
The Presence of Fibroblast Growth Factor in the Frog Egg: Its Role as a Natural Mesoderm Inducer
Authors: Kimelman David , Abraham Judith A. , Haaparanta Tapio , Palisi Thomas M. , Kirschner Marc W.
Published: October 2006

A complementary DNA clone corresponding to a 4.2-kilobase transcript that is present in the
Xenopus
oocyte and newly transcribed in the neurula stages of development has been isolated. This messenger RNA encodes a 155-amino acid protein that is 84% identical to the human basic fibroblast growth factor (bFGF). When expressed in
Escherichia coli
and purified, the
Xenopus
FGF induced mesoderm in animal cell blastomeres as measured by muscle actin expression. Immunoblots with an antibody to a
Xenopus
FGF peptide show that the oocyte and early embryo contain a store of the FGF polypeptide at high enough concentrations to induce mesoderm. The presence of FGF in the oocyte, together with the apparent lack of a secretory signal sequence in the protein, suggest that the regulation of mesoderm induction may involve novel mechanisms that occur after the translation of FGF.
The Brain in AIDS: Central Nervous System HIV-1 Infection and AIDS Dementia Complex
Authors: Price Richard W. , Brew Bruce , Sidtis John , Rosenblum Marc , Scheck Adrienne C. , Cleary Paul
Published: October 2006

Infection with human immunodeficiency virus type 1 (HIV-1) is frequently complicated in its late stages by the AIDS dementia complex, a neurological syndrome characterized by abnormalities in cognition, motor performance, and behavior. This dementia is due partially or wholly to a direct effect of the virus on the brain rather than to opportunistic infection, but its pathogenesis is not well understood. Productive HIV-1 brain infection is detected only in a subset of patients and is confined largely or exclusively to macrophages, microglia, and derivative multinucleated cells that are formed by virus-induced cell fusion. Absence of cytolytic infection of neurons, oligodentrocytes, and astrocytes has focused attention on the possible role of indirect mechanisms of brain dysfunction related to either virus or cell-coded toxins. Delayed development of the AIDS dementia complex, despite both early exposure of the nervous system to HIV-1 and chronic leptomeningeal infection, indicates that although this virus is "neurotropic," it is relatively nonpathogenic for the brain in the absence of immunosuppression. Within the context of the permissive effect of immunosuppression, genetic changes in HIV-1 may underlie the neuropathological heterogeneity of the AIDS dementia complex and its relatively independent course in relation to the systemic manifestations of AIDS noted in some patients.
The
RAD9
Gene Controls the Cell Cycle Response to DNA Damage in
Saccharomyces cerevisiae
Authors: Weinert Ted A. , Hartwell Leland H.
Published: October 2006

Cell division is arrested in many organisms in response to DNA damage. Examinations of the genetic basis for this response in the yeast
Saccharomyces cerevisiae
indicate that the
RAD9
gene product is essential for arrest of cell division induced by DNA damage. Wild-type haploid cells irradiated with x-rays either arrest or delay cell division in the G2 phase of the cell cycle. Irradiated G1 and M phase haploid cells arrest irreversibly in G2 and die, whereas irradiated G2 phase haploid cells delay in G2 for a time proportional to the extent of damage before resuming cell division. In contrast, irradiated
rad9
cells in any phase of the cycle do not delay cell division in G2, but continue to divide for several generations and die. However, efficient DNA repair can occur in irradiated
rad9
cells if irradiated cells are blocked for several hours in G2 by treatment with a microtubule poison. The
RAD9
-dependent response detects potentially lethal DNA damage and causes arrest of cells in G2 until such damage is repaired.
A Complete Mapping of the Proteins in the Small Ribosomal Subunit of
Escherichia coli
Authors: Capel M. S. , Engelman D. M. , Freeborn B. R. , Kjeldgaard M. , Langer J. A. , Ramakrishnan V. , Schindler D. G. , Schneider D. K. , Schoenborn B. P. , Sillers I.-Y. , Yabuki S. , Moore P. B.
Published: October 2006

The relative positions of the centers of mass of the 21 proteins of the 30
S
ribosomal subunit from
Escherichia coli
have been determined by triangulation using neutron scattering data. The resulting map of the quaternary structure of the small ribosomal subunit is presented, and comparisons are made with structural data from other sources.
Theoretical Studies of DNA During Gel Electrophoresis
Authors: Deutsch J. M.
Published: October 2006

A numerical study of the motion of a long-chain macromolecule in a gel has shown unexpected features. The application of a field appears to induce the chain to contract on itself. This is followed by its "unwinding" into an extended configuration. For long chains, the mobility tends toward a constant, in accord with experiments. For the parameter range used, the observed molecular motion differs strongly from assumptions made in the present theory of electrophoresis.
Viroid-Induced Phosphorylation of a Host Protein Related to a dsRNA-Dependent Protein Kinase
Authors: Hiddinga H. J. , Crum C. Jessen , Hu Jie , Roth D. A.
Published: October 2006

Viroids are very small, unencapsidated RNAs that replicate and induce severe disease in plants without encoding for any proteins. The mechanisms by which the viroid RNA regulates these events and interacts with host factors are unknown. An
M
r
68,000 host-encoded protein has been identified that is differentially phosphorylated in extracts from viroid-infected and mock-inoculated tissues. This phosphoprotein is immunologically related to a double-stranded (ds) RNA-dependent protein kinase from virus-infected, interferon-treated human cells. Further, nucleotide photoaffinity labeling indicates that the protein has an ATP binding site. This protein is similar to dsRNA-dependent protein kinases implicated in mammalian systems in the regulation of protein synthesis and virus replication.
Large Microtubule-Associated Protein of
T. brucei
Has Tandemly Repeated, Near-Identical Sequences
Authors: Schneider Andre , Hemphill Andrew , Wyler Toni , Seebeck Thomas
Published: October 2006

The parasitic protozoon
Trypanosoma brucei
contains a highly organized membrane skeleton, consisting of a dense array of parallel, singlet microtubules that are laterally interconnected and that are also in tight contact with the overlying cell membrane. A high molecular weight, heat-stable protein from this membrane skeleton was isolated that is localized along the microtubules. Protease digestion experiments and sequencing of a cloned gene segment showed that most of the protein is built up by more than 50 nearly identical tandem repeats with a periodicity of 38 amino acids.
Relaxation of Isolated Ventricular Cardiomyocytes by a Voltage-Dependent Process
Authors: Bridge John H. B. , Spitzer Kenneth W. , Ershler Philip R.
Published: October 2006

Cell contraction and relaxation were measured in single voltage-clamped guinea pig cardiomyocytes to investigate the contribution of sarcolemmal Na
+
-Ca
2+
exchange to mechanical relaxation. Cells clamped from -80 to 0 millivolts displayed initial phasic and subsequent tonic contractions; caffeine reduced or abolished the phasic and enlarged the tonic contraction. The rate of relaxation from tonic contractions was steeply voltage-dependent and was significantly slowed in the absence of a sarcolemmal Na
+
gradient. Tonic contractions elicited in the absence of a Na
+
gradient promptly relaxed when external Na
+
was applied, reflecting activation of Na
+
-Ca
2+
exchange. It appears that a voltage-dependent Na
+
-Ca
2+
exchange can rapidly mechanically relax mammalian heart muscle.
Paramecium
Fusion Rosettes: Possible Function as Ca
2+
Gates
Authors: Satir Birgit H. , Oberg Stephen G.
Published: October 2006

The function of a specific intramembrane particle array, "the fusion rosette," an essential requirement for exocytosis of trichocysts in
Paramecium
, was probed with a temperature sensitive secretory mutant (nd9). The cells were grown at 27°C, the nonpermissive, nonreleasing temperature at which fusion rosettes do not assemble. Exocytosis could be triggered, nonetheless, by addition of 40 μ
M
ionophore A23187 and 15 m
M
Ca
2+
but not Mg
2+
. Rosette function is bypassed by this procedure, suggesting that during normal release, the rosette acts as a Ca
2+
channel that allows development of a site-specific increase in Ca
2+
, which in turn induces fusion and release.
A Mutation of the Circadian System in Golden Hamsters
Authors: Ralph Martin R. , Menaker Michael
Published: October 2006

A mutation has been found that dramatically shortens the period of the circadian locomotor rhythm of golden hamsters. The pattern of inheritance of this mutation suggests that it occurred at a single, autosomal locus (
tau
). Wild-type animals have rhythms with free-running periods averaging about 24 hours; animals heterozygous for the mutation have periods of about 22 hours, whereas homozygous animals have rhythms with periods close to 20 hours. Animals that carry the mutant alleles exhibit abnormal entrainment to 24-hour light:dark cycles or are unable to entrain.
Prostacyclin: A Potentially Valuable Agent for Preserving Myocardial Tissue in Acute Myocardial Ischemia
Authors: Lefer Allan M. , Ogletree Martin L. , Smith J. Bryan , Silver Melvin J. , Nicolaou Kyriacos C. , Barnette William E. , Gasic Gregory P.
Published: October 2006

Prostacyclin, a potent, naturally occurring prostaglandin exerts a variety of cardiovascular and cellular actions of potential value in acute myocardial ischemia. These properties include the reduction of systemic blood pressure without changing heart rate, the lowering of coronary vascular and total peripheral resistance, the inhibition of platelet aggregation and the concomitant formation of thromboxane B
2
, and the reduction of the release of lysosomal enzymes.
Attraction by Repellents: An Error in Sensory Information Processing by Bacterial Mutants
Authors: Muskavitch Marc A. , Kort Edward N. , Springer Martin S. , Goy Michael F. , Adler Julius
Published: October 2006

Normal
Escherichia coli
bacteria are repelled by acetate, benzoate, and indole and attracted by α-aminoisobutyrate. We have isolated mutants that are attracted to acetate, benzoate, and indole and may be repelled by α-aminoisobutyrate. These reversed-taxis mutants are defective in a central processing component: a set of methylated proteins known as MCP 1. The mechanism of reversal of taxis is discussed.
Interleukin-2 Induction of T-Cell G
1
Progression and c-
myb
Expression
Authors: Stern Julie B. , Smith Kendall A.
Published: October 2006

In studies to determine the biochemical mechanisms responsible for cell proliferation, synchronized T cells were used as a model for cellular growth control. By metabolic and morphologic criteria, it was found that activation of the T-cell antigen receptor rendered the cells responsive to interleukin-2 (IL-2), but did not move them through the cell cycle. Instead, IL-2 stimulated G
1
progression to S phase, or lymphocyte "blastic transformation." During IL-2-promoted G
1
progression, expression of the cellular proto-oncogene c-
myb
was induced transiently at six to seven times basal levels, maximal levels occurring at the midpoint of G
1
.
Unique Forms of the
abl
Tyrosine Kinase Distinguish Ph
1
-Positive CML from Ph
1
-Positive ALL
Authors: Clark Steven S. , McLaughlin Jami , Crist William M. , Champlin Richard , Witte Owen N.
Published: October 2006

In the Philadelphia chromosome (Ph
1
) of chronic myelogenous leukemia (CML), the c-
abl
gene on chromosome 9 is translocated to
bcr
on chromosome 22. This results in the expression of a chimeric
bcr-abl
message that encodes the P210

bcr-abl

tyrosine kinase. The cells of 10% of acute lymphocytic leukemia patients (ALL) carry a cytogenetically similar Ph
1
translocation. We report that Ph
1
-positive ALL cells express unique
abl
-derived tyrosine kinases of 185 and 180 kilodaltons that are distinct from the
bcr-abl
-derived P210 protein of CML. The appearance of the 185/180-kilodalton proteins correlates with the expression of a novel 6.5-kilobase messenger RNA. Thus, similar genetic translocations in two different leukemias result in the expression of distinct c-
abl
-derived products.
Reversal of Chloroquine Resistance in
Plasmodium falciparum
by Verapamil
Authors: Martin Samuel K. , Oduola Ayo M. J. , Milhous Wilbur K.
Published: October 2006

The parasite
Plasmodium falciparum
, like neoplastic cells, develops resistance to multiple structurally unrelated drugs. If the mechanisms by which
P. falciparum
and neoplastic cells become resistant are similar, then it may be possible to reverse the resistance in the two types of cells by the same pharmacological agents. Verapamil, a calcium channel blocker, completely reversed chloroquine resistance in two chloroquine-resistant
P. falciparum
clones from Southeast Asia and Brazil. Verapamil reversed chloroquine resistance at the same concentration (1 × 10
-6
M
) as that at which it reversed resistance in multidrug-resistant cultured neoplastic cells. This same concentration of verapamil had no effect on chloroquine-sensitive parasites. Hence, chloroquine resistance in
P. falciparum
may fit the criteria for the multidrug-resistant phenotype.
Encystation and Expression of Cyst Antigens by
Giardia lamblia
in Vitro
Authors: Gillin Frances D. , Reiner David S. , Gault Michael J. , Douglas Herndon , Das Siddhartha , Wunderlich Annette , Sauch Judith F.
Published: October 2006

The cyst form of
Giardia lamblia
is responsible for transmission of giardiasis, a common waterborne intestinal disease. In these studies, encystation of
Giardia lamblia
in vitro was demonstrated by morphologic, immunologic, and biochemical criteria. In the suckling mouse model, the jejunum was shown to be a major site of encystation of the parasite. Small intestinal factors were therefore tested as stimuli of encystation. An antiserum that reacted with cysts, but not with cultured trophozoites was raised in rabbits and used as a sensitive probe for differentiation in vitro. Cultured trophozoites that were exposed to bile salts showed a more than 20-fold increase in the number of oval, refractile cells that reacted strongly with anticyst antibodies, and in the expression of major cyst antigens. Exposure to primary bile salts resulted in higher levels of encystation than exposure to secondary bile salts. These studies will aid in understanding the differentiation of an important protozoan pathogen.
Ras
p21 as a Potential Mediator of Insulin Action in
Xenopus
Oocytes
Authors: Korn Laurence Jay , Siebel Christian W. , McCormick Frank , Roth Richard A.
Published: October 2006

The oncogene protein product (p21) of the
ras
gene has been implicated in mediating the effects of a variety of growth factors and hormones. Microinjection of monoclonal antibody 6B7, which is directed against a synthetic peptide corresponding to a highly conserved region of p21 (amino acids 29 to 44) required for p21 function, specifically inhibited
Xenopus
oocyte maturation induced by incubation with insulin. The inhibition was dose-dependent and specific since (i) the same antibody had no effect on progesterone-induced maturation, (ii) immunoprecipitation and Western blotting indicated that the antibody recognized a single protein of molecular weight 21,000 in oocyte extracts, and (iii) inhibition was not observed with identical concentrations of normal immunoglobulin. Thus, p21 appears to be involved in mediating insulin-induced maturation of
Xenopus
oocytes. Furthermore, the mechanism may involve phosphorylation of p21, as p21 was found to be a substrate of the insulin receptor kinase.
Unusual Antibody-Induced Modulation of Surface Antigens in the Cell Coat of a Bloodstream Trypanosome
Authors: Giannini M. S. , D'Alesandro P. A.
Published: October 2006

Unlike other eukaryotic cells,
Trypanosoma lewisi
forms caps at 0°C when incubated with rabbit immunoglobulin G (IgG) directed against surface IgG from the rat host. The host IgG, which is specific for parasite antigens, probably does not cause capping of these antigens in vivo, since trypanosomes treated with Fab fragments directed against rat IgG are uniformly labeled and do not cap at 0°C or 37°C.
Antitrypanosomal Effect of Allopurinol: Conversion in Vivo to Aminopyrazolopyrimidine Nucleotides by
Trypanosoma cruzi
Authors: Marr J. Joseph , Berens Randolph L. , Nelson Donald J.
Published: October 2006

The parasite
Trypanosoma cruzi
metabolizes allopurinol by a sequential conversion to allopurinol mononucleotide and aminopurinol mononucleotide. The latter is incorporated into RNA. This transformation of a widely used innocuous agent, allopurinol, into a toxic adenine analog appears to account for the antiprotozoan effect of allopurinol. These unique enzymatic activities appear to occur only in
T. cruzi
and the pathogenic leishmaniae. Allopurinol may serve as a model for the synthesis of similar antiprotozoan agents.
A Small Gold-Conjugated Antibody Label: Improved Resolution for Electron Microscopy
Authors: Hainfeld James F.
Published: October 2006

A general method has been developed to make the smallest gold-conjugated antibody label yet developed for electron microscopy. It should have wide application in domainal mapping of single molecules or in pinpointing specific molecules, sites, or sequences in supramolecular complexes. It permits electron microscopic visualization of single antigen-binding antibody fragments (Fab′) by covalently linking an 11-atom gold cluster to a specific residue on each Fab′ such that the antigenic specificity and capacity are preserved. The distance of the gold cluster from the antigen is a maximum of 5.0 nanometers when the undecagold-Fab′ probe is used as an immunolabel.
Nuclear Power After Chernobyl
Authors: Ahearne John F.
Published: October 2006

The causes and progress of the accident at Chernobyl are described, and a comparison between the Chernobyl accident and the 1979 accident at the Three Mile Island nuclear power station is made. Significant similarities between Chernobyl and Three Mile Island include complacency of operators and industry, deliberate negation of safety systems, and a lack of understanding of their plant on the part of the operators, which shows the critical importance of the human element. The Chernobyl accident has implications for nuclear power in the United States; it will affect the research program of the Nuclear Regulatory Commission, regulation of Department of Energy reactors, new reactor designs, and public attitudes.
Neural Cell Adhesion Molecule: Structure, Immunoglobulin-Like Domains, Cell Surface Modulation, and Alternative RNA Splicing
Authors: Cunningham Bruce A. , Hemperly John J. , Murray Ben A. , Prediger Ellen A. , Brackenbury Robert , Edelman Gerald M.
Published: October 2006

The neural cell adhesion molecule, N-CAM, appears on early embryonic cells and is important in the formation of cell collectives and their boundaries at sites of morphogenesis. Later in development it is found on various differentiated tissues and is a major CAM mediating adhesion among neurons and between neurons and muscle. To provide a molecular basis for understanding N-CAM function, the complete amino acid sequences of the three major polypeptides of N-CAM and most of the noncoding sequences of their messenger RNA's were determined from the analysis of complementary DNA clones and were verified by amino acid sequences of selected CNBr fragments and proteolytic fragments. The extracellular region of each N-CAM polypeptide includes five contiguous segments that are homologous in sequence to each other and to members of the immunoglobulin superfamily, suggesting that interactions among immunoglobulin-like domains form the basis for N-CAM homophilic binding. Although different in their membrane-associated and cytoplasmic domains, the amino acid sequences of the three polypeptides appear to be identical throughout this extracellular region (682 amino acids) where the binding site is located. Variations in N-CAM activity thus do not occur by changes in the amino acid sequence that alter the specificity of binding. Instead, regulation is achieved by cell surface modulation events that alter N-CAM affinity, prevalence, mobility, and distribution on the surface. A major mechanism for modulation is alternative RNA splicing resulting in N-CAM's with different cytoplasmic domains that differentially interact with the cell membrane. Such regulatory mechanisms may link N-CAM binding function with other primary cellular processes during the embryonic development of pattern.
Clonal Restriction Boundaries in
Xenopus
Embryos Shown with Two Intracellular Lineage Tracers
Authors: Sheard Philip , Jacobson Marcus
Published: October 2006

It has been proposed that clonal restriction boundaries develop in
Xenopus
embryos between clones initiated at the 512-cell stage, and that these boundaries result in formation of morphological compartments, each populated by progeny of a group of ancestral cells. Although this hypothesis has gained some acceptance, it has also been criticized because the use of only one cell lineage tracer was not a conclusive test of the hypothesis. However, the critical experiment, an assessment of the extent of mingling between two labeled clones in the same embryo, has now been performed. A model of the proposed arrangement of the ancestral cell groups in the 512-cell embryo predicted that the two clones would remain separate in 49% of cases and intermingle in 51% of cases. In fact, there was a bimodal distribution, in which separation of the clones occurred in 46% of embryos and extensive interclonal mingling was observed in 54%. These results are not compatible with hypotheses in which a unimodal distribution of mingling would be predicted but are consistent with the compartment hypothesis.
Aedes albopictus
in North America: Probable Introduction in Used Tires from Northern Asia
Authors: Hawley William A. , Reiter Paul , Copeland Robert S. , Pumpuni Charles B. , Craig George B.
Published: October 2006

North American strains of
Aedes albopictus
, an Asian mosquito recently introduced into the Western Hemisphere, exhibit photoperiodic sensitivity and cold-hardiness characteristics similar to strains originating from temperate zone Asia. Trade statistics for used tire imports, the most likely mode of introduction, also indicate a north Asian origin.
Aedes albopictus
, an important vector of dengue and a potential vector of many other arboviral diseases, may therefore have the capability of infesting much of temperate North America.
Intercellular Communication in Pancreatic Islet Monolayer Cultures: A Microfluorometric Study
Authors: Kohen Elli , Kohen Cahide , Thorell Bo , Mintz Daniel H. , Rabinovitch Alexander
Published: October 2006

Single islet cells in monolayer cultures of neonatal rat pancreas were microinjected with fluorescein and scanned topographically by microfluorometry. Fluorescein spread from an injected islet cell directly into neighboring islet cells, and, in the presence of 16.7 millimolar glucose, significantly more islet cells communicated with the injected cell than in glucose-free medium. Islet cells were also microinjected with glycolytic substrates and activators that produced transient changes in cellular levels of reduced pyridine nucleotides-nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate [NAD(P)H]. Changes in NAD(P)H fluorescence were observed in islet cells incubated first for 18 hours in very low glucose concentrations and then in a glucose-free medium and injected with glycolytic substrates and activators; however, little change of fluorescence occurred in adjacent islet cells. In contrast, after adding 16.7 millimolar glucose to the medium, injection of glycolytic substrates and activators produced transient changes in NAD(P)H fluorescence in the injected cell and in neighboring cells.
A Visit to Chernobyl
Authors: Wilson Richard
Published: October 2006

Details of the accident at the Chernobyl nuclear power plant were given by Soviet experts at a special International Atomic Energy Agency meeting in Vienna, Austria, in August 1986. Several unanswered questions were made much clearer by a visit to the decontaminated and operating power plant at Chernobyl and by discussions with Soviet scientists. The visit gives us insights into the way the Soviets design their technology, the consequences of the accident, and the magnificent way they coped with the disaster. Although there are general conclusions to be drawn for the rest of the world, such as the realization that operators of technological systems can and will deliberately cut out safety systems, the primary specific conclusion is to be grateful that the West did not follow the Soviet route in its development of nuclear power.
The Fragile X Site in Somatic Cell Hybrids: An Approach for Molecular Cloning of Fragile Sites
Authors: Warren Stephen T. , Zhang Fuping , Licameli Greg R. , Peters Jeanne F.
Published: October 2006

Fragile X syndrome is a common form of mental retardation associated with a fragile site on the human X chromosome. Although fragility at this site is usually evident as a nonstaining chromatid gap, it remains unclear whether or not actual chromosomal breakage occurs. By means of somatic cell hybrids containing either a normal human X or a fragile X chromosome and utilizing two genes that flank the fragile site as markers of chromosome integrity, segregation of these markers was shown to be more frequent if they encompass the fragile site under appropriate culture conditions. Hybrid cells that reveal marker segregation were found to contain rearranged X chromosomes involving the region at or near the fragile site, thus demonstrating true chromosomal breakage within this area. Two independent translocation chromosomes were identified involving a rodent chromosome joined to the human X at the location of the fragile site. DNA analysis of closely linked, flanking loci was consistent with the position of the breakpoint being at or very near the fragile X site. Fragility at the translocation junctions was observed in both hybrids, but at significantly lower frequencies than that seen in the intact X of the parental hybrid. This observation suggests that the human portion of the junctional DNA may contain part of a repeated fragility sequence. Since the translocation junctions join heterologous DNA, the molecular cloning of the fragile X sequence should now be possible.
Ion Shower Milling: Its Application to Cell Membrane Removal
Authors: Sugaya Eiichi , Onozuka Minoru
Published: October 2006

A thickness of about 100 angstroms of the cell membrane of an isolated single freeze-dried neuron of the snail can be etched off with an ion shower milling machine. The calcium content of the cell membrane area was more than one-fifth of the whole cell. The calcium content of the cell membrane area increased during pentylenetetrazole-induced bursting activity.
The Growth and Composition of the U.S. Labor Force
Authors: Briggs Vernon M.
Published: October 2006

In sharp contrast with the experiences of all other industrialized nations, the size of the labor force of the United States is growing rapidly while, simultaneously, its age, gender, and ethnic composition are changing markedly. Consequently, human resource issues present an unprecedented challenge in the nation's quest to achieve a fully employed and equitable society. New public policies that focus on labor market adjustment policies will be required if these developments are to be a boon rather than a bane to the emerging postindustrial economy.
Conduction Velocity Variations Minimize Conduction Time Differences Among Retinal Ganglion Cell Axons
Authors: Stanford L. R.
Published: October 2006

The visual system is able to accurately represent the spatiotemporal relations among the elements of a changing visual scene as the image moves across the retinal surface. This precise spatiotemporal mapping occurs despite great variability in retinal position and conduction velocity even among retinal ganglion cells of the same physiological class—a variability that would seem to reduce the precision with which spatiotemporal information can be transmitted to central visual areas. There was a strong negative relation between the intraretinal and extraretinal conduction time for axons of individual ganglion cells of the X-cell class. The effect of this relation was to produce a nearly constant total transmission time between the soma of a retinal X cell and its central target site. Thus, the variation in the conduction velocities of retinal ganglion cell axons may ensure that, regardless of the constraints imposed by retinal topography, a precise spatiotemporal central representation of the retinal image is maintained.
N
-Formyliminodiacetic Acid, a New Compound from the Reaction of Nitrilotriacetic Acid and Chlorine
Authors: Spanggord Ronald J. , Tyson Charles A.
Published: October 2006

It has been proposed that nitrilotriacetic acid be substituted for trisodium polyphosphates in detergents as a way to reduce the rate of eutrophication in the Great Lakes Basin. The reaction of nitrilotriacetic acid with chlorine-containing solutions produces a hitherto unknown degradation product,
N
-formyliminodiacetic acid, in high yield. The toxicological and environmental implications of this reaction are unclear.
Structurally Distinct, Stage-Specific Ribosomes Occur in
Plasmodium
Authors: Gunderson J. H. , Sogin M. L. , Wollett G. , Hollingdale M. , de la Cruz V. F. , Waters A. P. , McCutchan T. F.
Published: October 2006

Two structurally distinct nuclear genes code for cytoplasmic small subunit ribosomal RNA's in the parasite
Plasmodium berghei
. Stable transcripts from one of the ribosomal RNA genes are found almost exclusively in those stages of the life cycle that develop in the mosquito. When the parasite infects the mammalian host, transcripts from the second gene become the predominant small subunit ribosomal RNA species.
Genetic Reconstitution of Functional Acetylcholine Receptor Channels in Mouse Fibroblasts
Authors: Claudio Toni , Green W. N. , Hartman Deborah S. , Hayden Deborah , Paulson Henry L. , Sigworth F. J. , Sine Steven M. , Swedlund Anne
Published: October 2006

Foreign genes can be stably integrated into the genome of a cell by means of DNA-mediated gene transfer techniques, and large quantities of homogenous cells that continuously express these gene products can then be isolated. Such an expression system can be used to study the functional consequences of introducing specific mutations into genes and to study the expressed protein in the absence of cellular components with which it is normally in contact. All four
Torpedo
acetylcholine receptor (AChR) subunit complementary DNA's were introduced into the genome of a mouse fibroblast cell by DNA-mediated gene transfer. A clonal cell line that stably produced high concentrations of correctly assembled cell surface AChR's and formed proper ligand-gated ion channels was isolated. With this new expression system, recombinant DNA, biochemical, pharmacological, and electrophysiological techniques were combined to study
Torpedo
AChR's in a single intact system. The physiological and pharmacological profiles of
Torpedo
AChR's expressed in mouse fibroblast cells differ in some details from those described earlier, and may provide a more accurate reflection of the properties of this receptor in its natural environment.
Stable Amplified DNA in Drug-Resistant
Leishmania
Exists as Extrachromosomal Circles
Authors: Garvey Edward P. , Santi Daniel V.
Published: October 2006

The relative stability of amplified DNA in drug-resistant
Leishmania major
was previously reported to be dependent on location, that is, unstable amplified DNA was extrachromosomal and stable amplified DNA was chromosomal. Leishmanial chromosomes have now been directly examined by means of orthogonal-field-alternation gel electrophoresis (OFAGE). The amplified DNA's in three resistant cell lines displayed unusual migration and were clearly extrachromosomal, regardless of whether the amplified DNA's were stable or unstable. Thus, contrary to conclusions from earlier studies of drug resistance in cultured animal cells, stable amplified DNA in
Leishmania
can be extrachromosomal. In addition, these amplified DNA's were shown to be circular on the basis of their resistance to exonuclease III digestion and their behavior on OFAGE. Their mobility was also greatly changed after treatment with topoisomerase II, suggesting that the amplified DNA's were either supercoiled or concatenated circles.
Cross-Regulatory Interactions Among Pair-Rule Genes in
Drosophila
Authors: Harding Katherine , Rushlow Christine , Doyle Helen J. , Hoey Timothy , Levine Michael
Published: October 2006

The pair-rule genes of
Drosophila
are required for the subdivision of the developing embryo into a repeating series of homologous body segments. One of the pair-rule genes,
even-skipped
(
eve
), appears to be particularly important for the overall segmentation pattern since
eve
-
embryos lack all segmental subdivisions in the middle body region. On the basis of homeo box cross-homology we have isolated a gene, S72, which probably corresponds to
eve
. In embryo tissue sections S72 transcripts show a periodic distribution pattern. The
eve
-
phenotype appears to involve altered patterns of
fushi tarazu
and
engrailed
expression. These and other findings suggest that pair-rule gene expression might involve hierarchical cross-regulatory interactions.
Inosine May Be an Endogenous Ligand for Benzodiazepine Receptors on Cultured Spinal Neurons
Authors: MacDonald J. Ferguson , Barker Jeffery L. , Paul Steven M. , Marangos Paul J. , Skolnick Philip
Published: October 2006

Mouse spinal neurons grown in tissue culture were used to study the membrane effects of the benzodiazepine flurazepam and the naturally occurring purine nucleoside inosine, which competes for benzodiazepine receptor sites in the central nervous system. Application of inosine elicited two types of transmitter-like membrane effects: a rapidly desensitizing excitatory response and a nondesensitizing inhibitory response. Flurazepam produced a similar excitatory response which showed cross-desensitization with the purine excitation. Flurazepam also blocked the inhibitory inosine response. The results provide electrophysiological evidence that an endogenous purine can activate two different conductances on spinal neurons and that flurazepam can activate one of the conductances and antagonize the other.
URF6, Last Unidentified Reading Frame of Human mtDNA, Codes for an NADH Dehydrogenase Subunit
Authors: Chomyn Anne , Cleeter Michael W. J. , Ragan C. Jan , Riley Marcia , Doolittle Russell F. , Attardi Giuseppe
Published: October 2006

The polypeptide encoded in URF6, the last unassigned reading frame of human mitochondrial DNA, has been identified with antibodies to peptides predicted from the DNA sequence. Antibodies prepared against highly purified respiratory chain NADH dehydrogenase from beef heart or against the cytoplasmically synthesized 49-kilodalton iron-sulfur subunit isolated from this enzyme complex, when added to a deoxycholate or a Triton X-100 mitochondrial lysate of HeLa cells, specifically precipitated the URF6 product together with the six other URF products previously identified as subunits of NADH dehydrogenase. These results strongly point to the URF6 product as being another subunit of this enzyme complex. Thus, almost 60% of the protein coding capacity of mammalian mitochondrial DNA is utilized for the assembly of the first enzyme complex of the respiratory chain. The absence of such information in yeast mitochondrial DNA dramatizes the variability in gene content of different mitochondrial genomes.
Characterization of T Cell Receptor Gamma Chain Expression in a Subset of Murine Thymocytes
Authors: Lew Andrew M. , Pardoll Drew M. , Maloy W. Lee , Fowlkes B. J. , Kruisbeek Ada , Cheng Shi-Fey , Germain Ronald N. , Bluestone Jeffrey A. , Schwartz Ronald H. , Coligan John E.
Published: October 2006

While much information exists about the structure and function of the clonally distributed T cell receptor (TCR) αβ heterodimer, little is known about the γ protein, the product of a third rearranging TCR gene. An antiserum to a carboxyl-terminal peptide common to several of the murine gamma chain constant regions and a monoclonal antibody to the murine T3 complex were used to identify products of this TCR gene family in a subpopulation of Lyt2
-
, L3T4
-
thymocytes. This subpopulation does not express TCRα or full-length TCRβ messenger RNA. The gamma chain is a 35-kilodalton (kD) protein that is disulfide-bonded to a 45-kD partner and is associated with the T3 complex. Analysis of the glycosylation pattern of this thymic gamma chain revealed that the major variable region gamma (Vγ) gene transcribed in activated peripheral T cells is absent from this subpopulation. The cells that bear this second T cell receptor may therefore represent a distinct lineage differentiating within the thymus.
Vertical Distribution of an Estuarine Snail Altered by a Parasite
Authors: Curtis Lawrence A.
Published: October 2006

Estuarine snails
Ilyanassa obsoleta
bearing larvae of the trematode
Gynaecotyla adunca
behave singularly in comparison with conspecifics lacking this parasite. Following high tides, and especially at night, infected snails were found stranded high on beaches and sandbars. Semiterrestrial crustaceans living well up on the shore serve as the next host, and the modified (induced) snail behavior is apparently a parasite adaptation facilitating cercarial transmission to these crustaceans. The altered behavior is unusual because of its apparent enhancement of host-to-host transmission by cercariae rather than predation, the process commonly recognized as being enhanced by parasitic modification of host behavior.
Cloning of a Gene Whose Expression Is Increased in Scrapie and in Senile Plaques in Human Brain
Authors: Wietgrefe S. , Zupancic M. , Haase A. , Chesebro B. , Race R. , Frey W. , Rustan T. , Friedman R. L.
Published: October 2006

A complementary DNA library was constructed from messenger RNA's extracted from the brains of mice infected with the scrapie agent. The library was differentially screened with the objectives of finding clones that might be used as markers of infection and finding clones of genes whose increased expression might be correlated with the pathological changes common to scrapie and Alzheimer's disease. A gene was identified whose expression is increased in scrapie. The complementary DNA corresponding to this gene hybridized preferentially and focally to cells in the brains of scrapie-infected animals. The cloned DNA also hybridized to the neuritic plaques found with increased frequency in brains of patients with Alzheimer's disease.
A New Role for DNA Virus Early Proteins in Viral Carcinogenesis
Authors: Lewis Andrew M. , Cook James L.
Published: October 2006

The T antigen proteins encoded by DNA tumor virus early genes are involved in the transformation of normal cells to immortalized neoplastic cells that may or may not be tumorigenic in immunocompetent animals. Studies have been made of the tumorigenicity of DNA virus-transformed cells and the interactions of these cells in vivo and in vitro with immunologically nonspecific host effector cells such as natural killer cells and macrophages. The results imply that the T proteins determine the capacity of transformed cells to induce tumors by governing the level of susceptibility that transformed cells express to destruction by such host cellular defenses.
Involvement of the
bcl
-2 Gene in Human Follicular Lymphoma
Authors: Tsujimoto Yoshihide , Cossman Jeffrey , Jaffe Elaine , Croce Carlo M.
Published: October 2006

Recombinant DNA probes were cloned for the areas flanking the breakpoint on chromosome 18 in cells from a patient with acute lymphocytic leukemia of the B-cell type; cells of this line carry the t(14;18) chromosomal translocation. Two of the probes detected DNA rearrangements in approximately 60 percent of the cases of follicular lymphoma screened. In follicular lymphoma, most of the breakpoints in band q21 of chromosome 18 were clustered within a short stretch of DNA, approximately 2.1 kilobases in length. Chromosome 18-specific DNA probes for the areas flanking the breakpoints also detected RNA transcripts 6 kilobases in length in various cell types. The gene coding for these transcripts (the
bcl
-2 gene) seems to be interrupted in most cases of follicular lymphomas carrying the t(14;18) chromosomal translocation.
Genetic Damage, Mutation, and the Evolution of Sex
Authors: Bernstein Harris , Byerly Henry C. , Hopf Frederic A. , Michod Richard E.
Published: October 2006

The two fundamental aspects of sexual reproduction, recombination and outcrossing, appear to be maintained respectively by the advantages of recombinational repair and genetic complementation. Genetic variation is produced as a by-product of recombinational repair, but it may not be the function of sexual reproduction.