bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of in vivo-administered 2,3,7,8-tetrachlorodibenzo-p-dioxin on receptor binding of epidermal growth factor in the hepatic plasma membrane of rat, guinea pig, mouse, and hamster.
Authors: Madhukar B V , Brewster D W , Matsumura F
Published: May 2006

The effect of in vivo-administered 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on epidermal growth factor (EGF) receptor activity of the rat hepatic plasma membrane was studied. TCDD causes a significant reduction in EGF binding at an early stage of toxicity (day 2) and at very low doses (1 microgram/kg, single i.p., rat). This reduction appears to be due to a decline in the number of receptors. There is a good correlation between levels of decline in EGF binding and loss of body weight among TCDD-treated rats. The reduction in EGF binding occurs at a relatively low dose in the guinea pig (a very sensitive species) and at high doses in the hamster (a tolerant species). Among three mice strains, TCDD (115 micrograms/kg, single i.p.) caused 98% reduction in EGF binding in the sensitive strains (C57BL/6J and CBA/J) but only a 50% reduction in the tolerant strain (AKR/J). To relate the above biochemical changes to in vivo effects, TCDD was postnatally administered (through mother's milk) to mouse neonates. The most prominent toxic manifestations were early eye opening and incisor eruption, loss in body weight gain, and retardation of hair growth. All of these symptoms have been ascribed to EGF effects. TCDD was also found to stimulate phosphorylation of the EGF receptor in the rat hepatic plasma membrane. This phosphorylation effect was observed at day 1 and persisted until the end of the test (day 10). It has long been recognized that agents causing reduction in number of EGF receptors (e.g., phorbol esters) elicit in vivo cellular responses that are similar to those caused by exposure to excess doses of growth factors. Accordingly, a hypothesis has been proposed to ascribe some of the EGF-like effects of TCDD, such as fatty infiltration of the liver and hyperplastic proliferation of gastric epithelia and epidermal cells to its action on the EGF receptor.
Colony-stimulating factor (CSF) controls proliferation of CSF-dependent cells by acting during the G1 phase of the cell cycle.
Authors: Pluznik D H , Cunningham R E , Noguchi P D
Published: May 2006

Proliferation of granulocyte/macrophage (GM) progenitor cells in soft agar cultures is dependent on the continuous presence of colony-stimulating factors (CSF). To elucidate this dependency we studied the effect of deprivation and readdition of CSF on the cell cycle kinetics of a GM-CSF-dependent murine mast/basophil cell line (PT-18). Flow cytometry and [3H]thymidine incorporation have been used to analyze the complete cell cycle. Removal of CSF from the culture medium resulted in accumulation of the cells in the G1 phase. Eighteen hours after removal of CSF, 85% of the cells were arrested in G1 phase. Readdition of GM-CSF to such quiescent cells was followed by progression of the cells from G1 into S phase with a lag period of 10 hr. A similar lag period was observed when cells released from G2+M arrest progressed, in the presence of CSF, to S phase via the G1 phase. These findings indicate that deprivation of GM-CSF does not move PT-18 cells out of the cycle to a G0 phase but rather arrests them at early G1 phase. Finally, we demonstrate that, for the cells to progress through the cell cycle, the requirement for the presence of GM-CSF is limited to the first 6 hr of the 10-hr duration of the G1 phase.
Epidermal growth factor rapidly induces a redistribution of transferrin receptor pools in human fibroblasts.
Authors: Wiley H S , Kaplan J
Published: May 2006

Treatment of human fibroblasts with epidermal growth factor (EGF) results in a rapid increase (less than 5 min) in the ability of the cells to bind 125I-labeled transferrin to surface receptors. Scatchard analyses of EGF-treated cells indicate that this increase was due to an increase in the number of transferrin receptors at the cell surface rather than to alterations in ligand-receptor affinity. The EGF-induced increase in transferrin receptors was transient, reaching a peak by 5 min and then declining back to near basal levels by 45 min. Increases in transferrin receptor number were observed when approximately equal to 1% of the EGF receptors were occupied and were maximal at 16% occupancy. EGF treatment accelerated the rate at which previously internalized 125I-labeled transferrin-receptor complexes were returned to the cell surface. The kinetics and magnitude of the loss of intracellular transferrin receptors was sufficient to account for the increase in surface transferrin receptors. We conclude from these studies that one of the earliest effects of EGF treatment is the induced translocation of an intracellular compartment to the cell surface. This intracellular compartment contains transferrin receptors and may be part of the pathway involved in the normal recycling of cell surface proteins.
Infection of human endothelial cells by human T-lymphotropic virus type I.
Authors: Ho D D , Rota T R , Hirsch M S
Published: May 2006

We studied the effects of human T-lymphotropic virus type I (HTLV-I) on human endothelial cells in vitro. During cocultivation with an HTLV-I producer cell line (C91/PL), endothelial cells formed characteristic multinucleated syncytial giant cells. Inoculation with concentrated cell-free supernatant fluid from C91/PL cultures produced similar cytopathic effects, which were neutralized by pretreatment with HTLV-I specific human serum. HTLV-I antigens were detected in the cytoplasm of the multinucleated cells by indirect immunofluorescence. When endothelial cells showed maximal cytopathic changes, reverse transcriptase activity was demonstrated in the supernatant fluid and HTLV-I was isolated by cocultivation with peripheral blood mononuclear cells. This study demonstrates that HTLV-I tropism is not limited to lymphoid cells but extends to human endothelial cells as well.
Absence of RNase H allows replication of pBR322 in Escherichia coli mutants lacking DNA polymerase I.
Authors: Kogoma T
Published: May 2006

rnh (formerly termed sdrA) mutants of Escherichia coli K-12, capable of continuous DNA replication in the absence of protein synthesis (stable DNA replication), are devoid of ribonuclease H (RNase H, EC 3.1.26.4) activity. Plasmid pBR322 was found to replicate in rnh mutants in the absence of DNA polymerase I, the polA gene product, which is normally required for replication of this plasmid. The plasmid copy number in polA rnh double mutants was as high as in the wild-type strains. When a chimeric construct between pBR322 and pSC101 was introduced into a polA rnh double mutant, the replication of the plasmid via the pBR322 replicon was inhibited if the plasmid also carried an rnh+ gene or if the host harbored an F' plasmid carrying an rnh+ gene. Thus, DNA polymerase I-independent replication of pBR322 requires the absence of RNase H activity. This alternative mechanism requiring neither DNA polymerase I nor RNase H appears to involve a transcriptional event in the region of the normal origin of replication.
The retrovirus pol gene encodes a product required for DNA integration: identification of a retrovirus int locus.
Authors: Panganiban A T , Temin H M
Published: May 2006

We mutagenized cloned spleen necrosis virus DNA to identify a region of the retrovirus genome encoding a polypeptide required for integration of viral DNA. Five plasmids bearing different lesions in the 3' end of the pol gene were examined for the ability to integrate or replicate following transfection of chicken embryo fibroblasts. Transfection with one of these DNAs resulted in the generation of mutant virus incapable of integrating but able to replicate at low levels; this phenotype is identical to that of mutants bearing alterations in the cis-acting region, att. To determine whether the 3' end of the pol gene encodes a protein that interacts with att, we did a complementation experiment. Cells were first infected with an att- virus and then superinfected with the integration-deficient virus containing a lesion in the pol gene and a wild-type att site. The results showed that the att- virus provided a transacting function allowing integration of viral DNA derived from the mutant bearing a wild-type att site. Thus, the 3' end of the pol gene serves as an "int" locus and encodes a protein mediating integration of retrovirus DNA through interaction with att.
Replication of the broad host range plasmid RSF1010: requirement for three plasmid-encoded proteins.
Authors: Scherzinger E , Bagdasarian M M , Scholz P , Lurz R , Rückert B , Bagdasarian M
Published: May 2006

Cloning of specific regions of plasmid RSF1010, in conjunction with in vitro replication studies, has revealed three novel genes: repA, repB, and repC. They are clustered in one region of the plasmid, separated from the origin of replication by regions that are not essential for plasmid viability in an Escherichia coli host. In vivo, a 2.1-kilobase segment of the plasmid, bearing the replication origin, can establish itself as an autonomous replicon if the DNA region carrying the three rep genes is present in the same cell on an independent plasmid. In vitro, RSF1010 DNA is efficiently replicated by an ammonium sulfate fraction from the E. coli extract, provided the extracts are prepared from cells that can supply the required rep gene products. Using cells containing the cloned rep gene region as a source of elevated levels of the rep proteins, we have partially purified these proteins in functional form. When added to an enzyme fraction derived from plasmid-free cells, they specifically promote the replication of plasmid DNA bearing the RSF1010 origin.
Sequence homology and structural similarity between cytochrome b of mitochondrial complex III and the chloroplast b6-f complex: position of the cytochrome b hemes in the membrane.
Authors: Widger W R , Cramer W A , Herrmann R G , Trebst A
Published: May 2006

The amino acid sequences of cytochrome b of complex III from five different mitochondrial sources (human, bovine, mouse, yeast, and Aspergillus nidulans) and the chloroplast cytochrome b6 from spinach show a high degree of homology. Calculation of the distribution of hydrophobic residues with a "hydropathy" function that is conserved in this family of proteins implies that the membrane-folding pattern of the 42-kilodalton (kDa) mitochondrial cytochromes involves 8-9 membrane-spanning domains. The smaller 23-kDa chloroplast cytochrome appears to fold in five spanning domains that are similar to the first five of the mitochondria. Four highly conserved histidines are considered to be the likely ligands for the two hemes. The positions of the histidines along the spanning segments and in a cross section of the membrane-spanning alpha helices implies that two ligand pairs, His-82-His-197/198 and His-96-His-183, bridge the spanning peptides II and V, and the two hemes reside on opposite sides of the hydrophobic membrane core. In addition, the 17-kDa protein of the chloroplast b6-f complex appears to contain one or more of the functions of the COOH-terminal end of the mitochondrial cytochrome b polypeptide.
Androgen induction of ornithine decarboxylase mRNA in mouse kidney as studied by complementary DNA.
Authors: Kontula K K , Torkkeli T K , Bardin C W , Jänne O A
Published: May 2006

To investigate the mechanisms by which androgens regulate ornithine decarboxylase (OrnDCase; L-ornithine carboxy-lyase, EC 4.1.1.17) in mouse kidney, a cDNA clone encoding OrnDCase mRNA was prepared. Purification of OrnDCase mRNA from kidneys of androgen-treated mice was accomplished by immunoadsorption of renal polysomes to a protein A-Sepharose column and enrichment for poly(A)-containing RNA by oligo(dT)-cellulose. Double-stranded cDNA synthesized from this mRNA was inserted into the Pst I site of plasmid pBR322 by using oligo(dG . dC)-tailing and was propagated in Escherichia coli. Plasmids containing cDNA sequences coding for OrnDCase were identified by differential colony hybridization, by radioimmunological detection of OrnDCase-like antigens in bacterial cultures, and by cell-free translation of hybrid-selected mRNA followed by immunoprecipitation with monospecific OrnDCase antiserum. A restriction endonuclease fragment of the selected plasmid DNA (pODC54) was labeled by nick-translation and used to study changes in OrnDCase mRNA concentration. After a single dose of testosterone, renal OrnDCase mRNA concentration increased as soon as 6 hr and peaked 24 hr after steroid injection, as measured by RNA blot hybridization. Continuous androgen treatment for 4 days resulted in a 10- to 20-fold increase in OrnDCase mRNA concentration in normal animals, but no induction of this mRNA was detected in mice that have an inherent defect of the androgen receptor (testicular feminization). These results indicate that androgens regulate OrnD-Case synthesis in mouse kidney, at least in part, by increasing OrnDCase mRNA accumulation.
Periodicity of extinctions in the geologic past.
Authors: Raup D M , Sepkoski J J
Published: May 2006

The temporal distribution of the major extinctions over the past 250 million years has been investigated statistically using various forms of time series analysis. The analyzed record is based on variation in extinction intensity for fossil families of marine vertebrates, invertebrates, and protozoans and contains 12 extinction events. The 12 events show a statistically significant periodicity (P less than 0.01) with a mean interval between events of 26 million years. Two of the events coincide with extinctions that have been previously linked to meteorite impacts (terminal Cretaceous and Late Eocene). Although the causes of the periodicity are unknown, it is possible that they are related to extraterrestrial forces (solar, solar system, or galactic).
Snail shape and growth rates: Evidence for plastic shell allometry in
Littorina littorea
Authors: Kemp Paul , Bertness Mark D.
Published: May 2006

The periwinkle
Littorina littorea
exhibits morphological variation among southern New England populations that appear to be genetically continuous. In dense populations, individuals have relatively elongate shells in comparison to individuals in sparse populations, which have rounder, globose shells. We experimentally demonstrate that this shell variation is a function of snail growth rate. Rapidly growing snails develop thin, globose shells that accommodate more body mass than thicker, more elongate shells. The implications of these results are discussed in relation to interpreting morphological variation in extant gastropods and in the molluscan fossil record.
Proviral deletions and oncogene base-substitutions in insertionally mutagenized c-myc alleles may contribute to the progression of avian bursal tumors.
Authors: Westaway D , Payne G , Varmus H E
Published: May 2006

Bursal lymphomas induced in chickens by avian leukosis viruses (ALVs) harbor proviral insertions that augment expression of an adjacent cellular oncogene, c-myc. To analyze such insertionally mutagenized c-myc genes in greater detail, we isolated molecular clones from two independent tumors. Precise proviral integration has occurred within the transcribed region of the c-myc gene in both mutant alleles. The proviruses bear different internal deletions that preclude the expression of the gag, pol, and env genes. The c-myc gene from bursal lymphoma LL4 contains a single copy of an ALV long terminal repeat (LTR), presumably the product of homologous recombination between LTRs at the ends of a normal provirus; the "solo" LTR is positioned in the correct orientation to act as a promoter for the c-myc gene. Bursal lymphoma LL3 contains an ALV provirus positioned upstream in the opposite transcriptional orientation to the coding exons of c-myc and deleted from a site within the leader region into the gag gene. In addition, the nucleotide sequence of the c-myc gene from tumor LL3 differs from the published sequence of the normal c-myc coding region at 3 positions of 180 determined. One of these changes, a silent nucleotide transition, is documented as a somatic mutation by restriction endonuclease mapping. It is flanked by two other candidate tumor-specific point mutations, one of which predicts an amino acid replacement, Pro----Thr at position 63. Thus, additional lesions that may affect the expression of viral genes and the quantity and nature of the putative c-myc gene product occur in provirally mutated c-myc alleles and may contribute to tumor progression.
Allelic inclusion in the pre-B-cell line 18-81.
Authors: Wabl M R , Beck-Engeser G B , Burrows P D
Published: May 2006

In an Abelson-virus-transformed mouse lymphoid cell line with pre-B-cell characteristics, a few cells continuously produce heavy chains from both homologs. Each chain has a different variable region. These cells thereby exhibit allelic inclusion rather than allelic exclusion.
Prothymosin alpha: isolation and properties of the major immunoreactive form of thymosin alpha 1 in rat thymus.
Authors: Haritos A A , Goodall G J , Horecker B L
Published: May 2006

A polypeptide containing approximately equal to 112 amino acid residues, with the thymosin alpha 1 sequence at its NH2 terminus, has been isolated from rat thymus by using a radioimmunoassay with an antibody prepared against synthetic thymosin alpha 1. The new polypeptide, named "prothymosin alpha," was found to be the major substance crossreacting with thymosin alpha 1 antiserum in rat thymus extracts; peptides corresponding to thymosin alpha 1 or thymosin alpha 11 were not detected. In gel filtration at pH 2.8, prothymosin alpha emerged as a single symmetrical peak corresponding to an apparent molecular weight of 32,000, approximately 3 times larger than the minimum molecular weight calculated from its amino acid composition. On the same gel filtration columns, synthetic thymosin alpha 1 (calculated Mr = 3108) emerged at a position corresponding to a molecular weight of 10,000-11,000. Thus, both prothymosin alpha and thymosin alpha 1 appear to exist in solution as oligomers, possibly as trimers. Prothymosin alpha and synthetic thymosin alpha 1 also were separated readily in reverse-phase HPLC and in isoelectric focusing; the isoelectric point of prothymosin alpha determined by the latter procedure was found to be 3.55, consistent with an unusually high content of glutamic and aspartic acids based on amino acid analyses. Prothymosin alpha appears to represent the native polypeptide from which thymosin alpha 1 and other fragments are generated during the isolation of thymosin fraction 5.
On the use of sequence homologies to predict protein structure: identical pentapeptides can have completely different conformations.
Authors: Kabsch W , Sander C
Published: May 2006

The search for amino acid sequence homologies can be a powerful tool for predicting protein structure. Discovered sequence homologies are currently used in predicting the function of oncogene proteins. To sharpen this tool, we investigated the structural significance of short sequence homologies by searching proteins of known three-dimensional structure for subsequence identities. In 62 proteins with 10,000 residues, we found that the longest isolated homologies between unrelated proteins are five residues long. In 6 (out of 25) cases we saw surprising structural adaptability: the same five residues are part of an alpha-helix in one protein and part of a beta-strand in another protein. These examples show quantitatively that pentapeptide structure within a protein is strongly dependent on sequence context, a fact essentially ignored in most protein structure prediction methods: just considering the local sequence of five residues is not sufficient to predict correctly the local conformation (secondary structure). Cooperativity of length six or longer must be taken into account. Also, we are warned that in the growing practice of comparing a new protein sequence with a data base of known sequences, finding an identical pentapeptide sequence between two proteins is not a significant indication of structural similarity or of evolutionary kinship.
Induction of phenylalanine ammonia-lyase and 4-coumarate:CoA ligase mRNAs in cultured plant cells by UV light or fungal elicitor
Authors: Kuhn David N. , Chappell Joseph , Boudet Alain , Hahlbrock Klaus
Published: May 2006

The mRNAs encoding two enzymes of phenylpropanoid metabolism, phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) and 4-coumarate:CoA ligase (4CL; EC 6.2.1.12), were induced in cultured parsley cells (
Petroselinum hortense
) either by irradiation with UV light or by treatment with elicitor, a cell-wall fraction of the fungus
Phytophthora megasperma
f. sp.
glycinea
. Two-dimensional gel electrophoresis of the encoded PAL and 4CL proteins revealed that the mRNAs induced by either treatment were very similar if not identical. RNA blot hybridization with cDNAs complementary to these mRNAs was used to measure changes in the mRNA amounts at various times after either treatment. Total cellular PAL and 4CL mRNA amounts increased coordinately after UV irradiation to a maximum at 7 hr and then decreased to uninduced levels by 30 hr with the same kinetics as observed previously for the changes in the translational activities. Treatment with the fungal elicitor also caused coordinated, but more rapid, changes in PAL and 4CL mRNA translational activities, with a sharp peak occurring 3 hr after the addition of elicitor. Corresponding changes in mRNA amounts were observed only for 4CL, whereas the amount of PAL mRNA continued to increase at least up to 20 hr after elicitor addition. Our results suggest that parsley cells respond to UV irradiation or addition of fungal elicitor by increased rates of transcription of genes involved in the synthesis of compounds related to UV or disease resistance, respectively.
Developmental regulation of cytokeratins in cells of the rat mammary gland studied with monoclonal antibodies.
Authors: Allen R , Dulbecco R , Syka P , Bowman M , Armstrong B
Published: May 2006

We have isolated two monoclonal antibodies to cytokeratins and determined their cell specificities. They display interesting localization within the rat mammary gland. One (1A10) shows specificity for myoepithelial cells; the other (24B42) is specific for lumenal cells at various stages of development. These two monoclonal antibodies and three others to cytokeratin previously isolated were used in conjunction with antibodies to myosin and collagen IV to confirm and extend our previous findings on epithelial cell types and development within the mammary gland.
Cell adhesion and morphogenesis: the regulator hypothesis.
Authors: Edelman G M
Published: May 2006

A sequence for the genetic and molecular regulation of morphogenesis is proposed in terms of the regulator hypothesis which is intended to provide a specific molecular framework relating developmental genetics to evolution. The hypothesis derives from an analysis of the interactive morphogenetic roles of the primary processes of cell adhesion, cell movement, and embryonic induction during regulative development. According to the regulator hypothesis, the genes for cell adhesion molecules (CAMs) are expressed in schedules that are prior to and largely independent of those for cytodifferentiation. The expressed CAMs act as regulators of the overall patterns of those morphogenetic movements that are essential for inductive sequences or early milieu-dependent differentiations. It is proposed that, during evolution, natural selection eliminates those organisms in which variants of CAM gene expression or of morphogenetic movements or of both result in interruptions in the inductive sequence. Under this assumption, more than one (but not all) combinations of these two variables will lead to stabilization of the order of inductive sequences and of the body plan in a variety of species. Moreover, small variations in the pattern of action of regulatory genes for CAMs in those organisms that are not selected against could lead to large changes in animal form within relatively short periods of evolutionary time. The experimental bases for the regulator hypothesis are reviewed here in terms of the molecular properties of CAMs and their known spatio-temporal sequences of expression during early embryogenesis.
Elaboration of telomeres in yeast: recognition and modification of termini from Oxytricha macronuclear DNA.
Authors: Pluta A F , Dani G M , Spear B B , Zakian V A
Published: May 2006

The termini of macronuclear DNA molecules from the protozoan Oxytricha fallax share a common sequence and structure, both of which differ markedly from those deduced for yeast telomeres. Despite these differences, terminal restriction fragments from O. fallax macronuclear DNA can support telomere formation in yeasts. Two linear plasmids (LYX-1 and LYX-2) constructed by ligating BamHI-digested total Oxytricha macronuclear DNA to a yeast vector were analyzed. One end of LYX-1 and both ends of LYX-2 are derived from the Oxytricha DNA that encodes rRNA (rDNA) whereas the other end of LYX-1 is from an Oxytricha fragment other than rDNA. After propagation in yeast, both ends of LYX-1 and LYX-2 retain the C4A4 repeat characteristic of the O. fallax terminal sequence. In addition, both ends of both plasmids acquire 300-1000 base pairs of DNA containing the sequence (C-A)n, a sequence found near the termini of yeast chromosomes. Thus, at least two different Oxytricha termini display distinctive properties in yeast cells in that linear plasmids containing them are not degraded nor are they integrated into chromosomal DNA. These Oxytricha termini may act directly as telomeres in yeast; alternatively, the Oxytricha DNA may serve as a signal that results in the elaboration of a yeast telomere on the ciliate DNA.
Isolation of the specific glomerular basement membrane antigen involved in Goodpasture syndrome.
Authors: Wieslander J , Bygren P , Heinegård D
Published: May 2006

The antigen involved in the glomerulonephritis associated with antibodies to glomerular basement membrane (GBM) was purified from human GBM digested with highly purified clostridial collagenase. The purified nonreduced sample contained two components with closely similar mobilities on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. After reduction they moved as one, nonantigenic, component, corresponding to a molecular weight of 26,000. Immunologically identical aggregates of higher molecular weight (i.e., 48,000) were also identified in the crude digest. Reduction of such aggregates after purification released some protein with a molecular weight of 26,000, but a large proportion was insensitive to reduction. Seven patients with Goodpasture syndrome all had circulating anti-GBM antibodies directed only against the purified antigen.
Cultural and biological evolutionary processes: gene-culture disequilibrium.
Authors: Feldman M W , Cavalli-Sforza L L
Published: May 2006

The dynamics of the interaction between genetic and cultural transmission are studied by using a simple two-phenotype diallelic haploid genetic system. The value of an individual's phenotype is determined by cultural transmission from its parent or by a randomly chosen member of the parental population. In the absence of phenotypic selection, polymorphic equilibria of the gene and trait frequencies are obtained. The correlation between genotype and phenotype within or between populations depends on a quantity formally similar to linkage disequilibrium and is determined by a relationship among transmission coefficients analogous to a coefficient of epistasis. With natural selection on the phenotype and no mutation, only degenerate transmission rules allow polymorphic equilibria to be attained, and, in general, the genotype allowing the strongest transmission of the favored phenotype is successful.
On the evolution of altruism by kin selection
Authors: Matessi Carlo , Karlin Samuel
Published: May 2006

A general model for the evolution of altruism is formulated. Central to the model is a pair of local fitness functions, which prescribe the fitness of the altruist and selfish phenotypes as functions of the composition of local groups into which prereproductives are subdivided. When the local groups are sibships or other kin groups, the model is one for kin selection. Functions for cost and benefit of altruism are derived from the fitness functions. Conditions for evolution of altruism are then determined in terms of cost and benefit. It is shown that the Hamilton rule has quantitative validity only in the special case of linear fitness functions. Sufficient conditions are found for qualitative validity of the Hamilton rule. Qualitative violation of the rule is also possible.
Bombesin stimulates insulin secretion by a pancreatic islet cell line.
Authors: Swope S L , Schonbrunn A
Published: May 2006

The amphibian tetradecapeptide, bombesin (BBS) has been shown to stimulate insulin secretion both in vivo and by pancreatic islet cells in vitro. To determine whether BBS can act directly on pancreatic beta cells, we examined its effects on insulin secretion by HIT-T15 cells (HIT cells), a clonal islet cell line. Addition of 100 nM BBS to HIT cells stimulated insulin release 25-fold within 30 sec. The rapid stimulatory effect of BBS on insulin release was short-lived: the secretory rate returned to basal levels after 90 min of BBS treatment. The decrease in the rate of insulin release in the continued presence of BBS was due not to depletion of intracellular insulin stores but to specific desensitization to this peptide. Stimulation of insulin secretion by BBS was dose dependent with an ED50 value (0.51 +/- 0.15 nM) similar to the concentration of BBS-like immunoreactive material in rat plasma. Five BBS analogs, including porcine gastrin-releasing peptide, were as powerful as BBS in stimulating insulin release. The relative potencies of the analogs tested indicated that the COOH-terminal octapeptide sequence in BBS was sufficient for stimulation of release. In contrast, 14 peptides structurally unrelated to BBS did not alter insulin secretion. BBS action was synergistic with that of glucagon; insulin secretion in the presence of maximal concentrations of both peptides was greater than the additive effects of the two peptides added individually. Somatostatin inhibited BBS-stimulated release by 69 +/- 1% with an ID50 value of 3.2 +/- 0.3 nM. These results show that BBS stimulation of insulin secretion by a clonal pancreatic cell line closely parallels its effects in vivo and support the hypothesis that BBS stimulates insulin secretion by a direct effect on the pancreatic beta cell. The clonal HIT cell line provides a homogeneous cell preparation amenable for studies on the biochemical mechanisms of BBS action in the endocrine pancreas.
Metabolism of apolipoproteins B-48 and B-100 of triglyceride-rich lipoproteins in normal and lipoprotein lipase-deficient humans.
Authors: Stalenhoef A F , Malloy M J , Kane J P , Havel R J
Published: May 2006

The metabolism of apolipoproteins B-48 and B-100 (apo B-48 and B-100) in large triglyceride-rich lipoproteins (300 to 1500 A in diameter) has been compared in three normal subjects and two subjects with genetically determined deficiency of lipoprotein lipase. The triglyceride-rich lipoproteins were obtained from a lipoprotein lipase-deficient donor 4 hr after a fat-rich meal in order to obtain chylomicrons (containing apo B-48) and very low density lipoproteins (VLDL) (containing apo B-100), whose properties had not been modified by the action of this enzyme. The triglyceride-rich lipoproteins were labeled with 125I and injected intravenously into recipients who had fasted overnight. In normal recipients, most of the apo B-48 was removed from the blood within 15 min, and most of the apo B-100 was removed within 30 min. In the lipoprotein lipase-deficient recipients, most of the injected apo B-100 remained in the blood for more than 8 hr; removal of apo B-48 was only slightly more rapid. In all subjects, only trace amounts of either protein were found in lipoproteins more dense than 1.006 g/ml. The results indicate that (i) the removal of the apo B of both chylomicrons and large VLDL from the blood is dependent upon the hydrolysis of their component triglycerides by lipoprotein lipase, and (ii) little or no apo B-48 of chylomicrons or apo B-100 of large VLDL is converted appreciably to low density lipoproteins (LDL). Our results suggest that the reported variability of the conversion of VLDL to LDL may be related to the size and composition of the particles secreted from the liver. The rapid production of remnant particles that are removed efficiently by the liver may minimize the opportunity for further reactions leading to the formation of LDL.
Fiber-fiber interaction and tectal cues influence the development of the chicken retinotectal projection.
Authors: Thanos S , Bonhoeffer F , Rutishauser U
Published: May 2006

The development of the retinotectal projection has been studied by a new experimental approach combining antibodies against the nerve cell adhesion molecule (NCAM), and techniques for mapping neuronal pathways using rhodamine B isothiocyanate (RITC) crystals. Anti-NCAM Fab', which specifically inhibits neurite fasciculation, was injected into the eye cup of 4-day-old chicken embryos. After 4-6 days of development, a small RITC crystal was placed on the neural retina to stain selectively axons arising from a localized region. One day later the retina, optic nerve, and tectum were examined and the paths of the fluorescent retinal ganglion cell axons were traced. These studies have led to four observations: (i) The presence of anti-NCAM Fab' causes the axons to form a disordered nerve bundle at the optic fissure. (ii) Disorder produced in the optic nerve persists throughout the optic pathway up to the tectum. (iii) Many of the misrouted fibers growing on or near the tectal surface can at least partially correct their position. (iv) Late axons grow in straight tracks along other fibers and do not correct their position. Together the results suggest that formation of the retinotectal projection involves both reading of positional cues on the tectum by growth cones of early arriving retinal axons and the tracking of growth cones along preexisting fibers that normally belong to neighboring retinal ganglion cells.
Formaldehyde activation factor, tetrahydromethanopterin, a coenzyme of methanogenesis
Authors: Escalante-Semerena Jorge C. , Leigh John A. , Rinehart Kenneth L. , Wolfe Ralph S.
Published: May 2006

An oxygen-labile formaldehyde activation factor (FAF) was isolated in highly purified form by use of anoxic fractionation procedures. The molecular weight of FAF was determined to be 776 and that of methanopterin (MPT) 772 by fast-atom-bombardment mass spectrometry (FABMS). High-resolution FABMS measurements on MPT and FAF indicated molecular formulas of C
30
H
41
N
6
O
16
P and C
30
H
45
N
6
O
16
P, respectively. The presence of phosphorus was confirmed by 100-MHz
31
P NMR. The 360-MHz
1
H NMR spectrum of FAF in deuterium oxide was similar to that of MPT. A functional relationship between MPT and FAF was documented; both compounds stimulated the reductive demethylation of 2-(methylthio)ethanesulfonic acid (CH
3
-S-CoM) to CH
4
when formaldehyde oxidation provided a source of electrons, and FAF replaced MPT in the CH
3
-S-CoM-stimulated conversion of CO
2
to CH
4
under H
2
(the RPG effect). MPT was enzymically converted to FAF during the reduction of CH
3
-S-CoM, and HCHO to CH
4
under H
2
. Evidence indicates that FAF is tetrahydromethanopterin.
Nerve growth factor inhibits the synthesis of a single-stranded DNA binding protein in pheochromocytoma cells (clone PC12).
Authors: Biocca S , Cattaneo A , Calissano P
Published: May 2006

Arrest of mitosis and neurite outgrowth induced by nerve growth factor (NGF) in rat pheochromocytoma cells (clone PC12) is accompanied by a progressive inhibition of the synthesis of a protein that binds to single-stranded but not to double-stranded DNA. Time course experiments show that this inhibition is already apparent after a 2-day incubation with NGF and is maximum (85-95%) upon achievement of complete PC12 cell differentiation. Inhibition of the synthesis of this single-stranded DNA binding protein after 48 hr of incubation with NGF is potentiated by concomitant treatment of PC12 cells with antimitotic drugs acting at different levels of DNA replication. Purification on a preparative scale of this protein and analysis of its major physicochemical properties show that: (i) it constitutes 0.5% of total soluble proteins of naive PC12 cells; (ii) its molecular weight measured by NaDodSO4/PAGE is Mr 34,000 (sucrose gradient centrifugation under nondenaturing conditions yields a sedimentation coefficient s20,w of 8.1 S, indicating that the native protein is an oligomer); (iii) amino acid analysis demonstrates a preponderance of acidic over basic residues, while electrofocusing experiments show that it has an isoelectric point around 8.0; (iv) approximately 15% of the protein is phosphorylated in vivo. It is postulated that control of the synthesis of this protein is connected with activation of a differentiative program triggered by NGF in the PC12 neoplastic cell line at some step(s) of DNA activity.
Active oxygen acts as a promoter of transformation in mouse embryo C3H/10T1/2/C18 fibroblasts.
Authors: Zimmerman R , Cerutti P
Published: May 2006

There is much evidence from in vivo and in vitro carcinogenesis studies that active oxygen species play a role in tumor promotion. We tested directly whether superoxide produced extracellularly by xanthine-xanthine oxidase (X-XO) has the capacity to promote initiated mouse embryo C3H/10T1/2 fibroblasts. Cell cultures initiated with either 137Cs gamma-rays or benzo[a]pyrene diol epoxide I were found to transform 3-30 times more effectively when subsequently treated daily for 3 weeks with nontoxic doses of X-XO. Scavengers of active oxygen radicals such as superoxide dismutase or superoxide dismutase in combination with catalase reduced the frequency of appearance of transformed foci by 3-25 times when compared to cultures receiving X-XO alone. These results show that active oxygen species such as superoxide and H2O2 can act in a promotional manner that mimics the effects of the mouse skin promoter phorbol 12-myristate 13-acetate in this system. X-XO also acted as a weak complete carcinogen.
Interaction of the 2,6-dimethoxysemiquinone and ascorbyl free radicals with Ehrlich ascites cells: a probe of cell-surface charge.
Authors: Pethig R , Gascoyne P R , McLaughlin J A , Szent-Györgyi A
Published: May 2006

The rate of quenching by Ehrlich ascites cells of anionic 2,6-dimethoxy-p-semiquinone and ascorbyl free radicals is investigated as a function of cell concentration, the blocking of cell-surface sulfhydryl groups by N-ethylmaleimide, and the reduction of cell-surface charge by neuraminidase. The rate of quenching is found to be proportional to cell viability and to the number of free cell-surface sulfhydryl groups. The enzymatic action of neuraminidase results in an increase of the free radical quenching rate, indicating that this rate can be used as a probe of cell-surface charge. Measurements as a function of the ionic strength of the suspending electrolyte gave a value of -1.22 microC X cm-2 for the charge density at the ascites cell surface. This is equivalent to a surface membrane potential of -14 mV for a 150 mM NaCl electrolyte and is a value in good agreement with published electrophoresis data.
Leukotriene B4 action on endothelium mediates augmented neutrophil/endothelial adhesion.
Authors: Hoover R L , Karnovsky M J , Austen K F , Corey E J , Lewis R A
Published: May 2006

The attachment of human polymorphonuclear leukocytes (PMN) to bovine endothelial monolayers is increased by pretreatment of the endothelial cells with leukotriene B4 (LTB4). The response is dose dependent with a maximum at 10(-6) M, requires no more than 1 min of preincubation for the maximal effect, and decays linearly over 30 min once the LTB4 is removed. Preincubation of PMN with LTB4 does not augment subsequent adhesion to a plastic substratum or an untreated monolayer of endothelial cells and eliminates the augmented attachment to LTB4-pretreated endothelial cells. The simultaneous exposure of both cell types during the adhesion interaction gives a biphasic dose-related increment, suggesting that the inhibition of the neutrophil adherence is less marked than with a pretreatment interval. Thus, the LTB4-dependent adherence of PMN to endothelial cells is selectively mediated by endothelial cells, is dose related, is reversible upon removal of the agonist from the endothelial cells, and is opposed by the direct action of LTB4 on the PMN.
Effects of Cu deficiency on photosynthetic electron transport
Authors: Droppa Magdolna , Terry Norman , Horvath Gabor
Published: May 2006

The role of copper (Cu) in photosynthetic electron transport was explored by using Cu deficiency in sugar beet as an experimental approach. Copper influenced electron transport at two sites in addition to plastocyanin. Under mild deficiency (0.84 nmol of Cu per cm
2
of leaf area), electron transport between the two photosystems (PS) is inhibited but not electron transport within PS I or PS II measured separately. The chlorophyll/plastoquinone ratio was normal in Cu-deficient plants. However, the breakpoint in the Arrhenius plot of electron transport was shifted towards a higher temperature. It is concluded that Cu is necessary to maintain the appropriate membrane fluidity to ensure the mobility of plastoquinone molecules to transfer electrons between the two photosystems. Under severe deficiency (0.22 nmol of Cu per cm
2
of leaf area) both PS II and PS I electron transports were inhibited and to the same extent. PS II electron transport activity could not be restored by adding artificial electron donors. Polypeptides with
M
r
s of 28,000 and 13,500 were missing in Cu-deficient chloroplast membranes. In PS II particles prepared from normal chloroplasts of spinach, 2 atoms of Cu per reaction center are present. We conclude that Cu influences PS II electron transport either directly, by participation in electron transfer as a constituent of an electron carrier, or indirectly, via the polypeptide composition of the membrane in the PS II complex.
Imbalance of total cellular nucleotide pools and mechanism of the colchicine-induced cell activation.
Authors: Chou I N , Zeiger J , Rapaport E
Published: May 2006

Treatment with colchicine or vinblastine, both inhibitors of microtubule assembly, renders quiescent 3T3 cells in an "activated state" as evidenced by induction of DNA synthesis and other criteria. Microtubule disassembly caused by colchicine or vinblastine brings about a dramatic expansion of total cellular UTP pools with a concomitant diminution in total cellular ATP pools, thus resulting in a marked imbalance in total cellular nucleotide pools. Colchicine and vinblastine also stimulate total cellular RNA synthesis without enhancing uridine phosphorylation, suggesting that these drugs affect the G1 phase of the cell cycle at a point beyond the enhancement of uridine phosphorylation that usually accompanies mitogenic stimulation of quiescent mammalian cells. The markedly expanded cellular UTP pools appear to be necessary for initiation of the colchicine-stimulated DNA synthesis because decreasing cellular UTP pools by addition of D-glucosamine results in a selective inhibition of DNA synthesis in the colchicine-stimulated, but not control, cells. Furthermore, D-glucosamine exerts its inhibitory effect only when it is present in the cultures within the first 14 hr after colchicine treatment. When added at 21 hr, D-glucosamine still decreases cellular UTP pools, but it is no longer inhibitory for DNA synthesis, which commences 14-16 hr after colchicine stimulation. Taxol, an antitumor drug, prevents microtubule disassembly and also blocks such events as expansion of total cellular UTP pools and stimulation of RNA and DNA synthesis, indicating that microtubule depolymerization acts as a primary event initiating the process of cell activation induced by colchicine.
Role of cell surface immunoglobulin in B-lymphocyte activation.
Authors: LoCascio N J , Haughton G , Arnold L W , Corley R B
Published: May 2006

The role of cell surface immunoglobulin in helper T-cell-dependent B-cell activation was analyzed using a B-cell lymphoma, CH12, with known antigen specificity and activation properties similar to those of a resting B cell. Two sources of helper T cells were used, both selected such that they interact with H-2-encoded determinants on CH12 in the absence of the specific B-cell antigen, sheep erythrocytes. By this dissociation of the specificity of the T cells from that of the B cells, the requirement for antigen in the induction of CH12 to antibody secretion could be studied. The results show that both helper T-cell-B-cell interactions and surface immunoglobulin-antigen binding are involved in inducing B-cell differentiation, thus establishing a signalling function for the antigen receptor on B lymphocytes. Our data also show that the requirement for surface immunoglobulin-ligand interactions in B-cell activation can, under certain conditions, be circumvented, notably when high (nonphysiologic) multiplicities of T-cell help are used.
Ly-1 B cells: functionally distinct lymphocytes that secrete IgM autoantibodies.
Authors: Hayakawa K , Hardy R R , Honda M , Herzenberg L A , Steinberg A D , Herzenberg L A
Published: May 2006

Studies presented here introduce another perspective on the mechanisms responsible for IgM autoantibody production. A unique subpopulation of B lymphocytes (Ly-1 B) that concomitantly expresses IgM, IgD, Ia, and Ly-1 membrane glycoproteins is present at higher frequencies in NZB and NZB-related mice. The Ly-1 B subpopulation in these autoimmune animals is responsible for the "spontaneous" IgM secretion demonstrated with cultured NZB spleen cells and contains the cells that secrete typical NZB IgM autoantibodies to single-stranded DNA and to thymocytes. In addition, the Ly-1 B population in normal mouse strains (and in NZB) contains virtually all of the spleen cells that secrete IgM autoantibodies reactive with bromelain-treated mouse erythrocytes. Since a different B-cell subpopulation (IgM+, IgD-, Ly-1) secretes most of the IgM antibodies produced in responses to exogenous antigens, we conclude that Ly-1 B cells constitute a functionally distinct B-cell population important in certain kinds of autoimmunity.