Dynamic versus static indicators of threat: N2 and LPC modulation index attack intent and biological relevance during an affective Flanker task

Biological relevance may influence the neural response towards images which depict attack intent. In the present study, images featuring reptiles and firearms were employed as target and flanking stimuli in a modified version of the affective Flanker task. Forty-two participants (21 male) completed the modified Flanker task as EEG was recorded. Congruency effects in reaction times were more consistently observed for arrays with firearm targets than for arrays with reptile targets. Arrays with neutral targets (i.e., water pistols, turtles) evoked more negative mean N2 (250-400 ms) amplitudes than those with attack targets (i.e., attacking snakes, aimed handguns), while arrays with aimed handgun targets elicited more positive mean activity for the late positive component (LPC; 450-650 ms) compared to arrays with water pistol or reptile targets. Congruency effects were also found in N2 activity for arrays with firearm targets and reptile Flankers. In addition, LPC amplitude for incongruent arrays with attack targets and neutral Flankers was reduced compared to congruent attack arrays. These findings suggest that biological relevance influences interference processing (the N2) and intersects with attack intent during the later stages of picture processing (the LPC).

Deconstructing threat: Rethinking the interplay between biological and social relevance in the emotional salience of unpleasant images

The type of threat shown in an image influences the emotional salience of unpleasant images. Seventy-four participants (21 male) rated high threat, moderate threat, and neutral images featuring reptiles, firearms, or humans as electroencephalographic activity was recorded. The magnitude of P3b amplitudes coincided with the threat level of firearm and human images, whereas scenes of attacking snakes and aimed handguns evoked more positive late positive component (LPC) activity than non-attacking or neutral versions of these same stimuli. The lateralised early posterior negativity (EPN) in temporal occipital regions was most negative for firearms, followed by reptiles, and then humans, while the midline EPN in occipital regions was most negative for reptiles, followed by firearms, and then humans. These findings imply late event-related potential positivity is influenced by social relevance (the P3b) or the level of aggression displayed by the stimulus (the LPC), whereas stimulus type may be indexed by EPN modulation.

Contrast sensitivity and motion discrimination in cannabis users

RATIONALE

Cannabis use impairs visual attention; however, it is unclear whether cannabis use also impairs low level visual processing or whether low level visual deficits can be related to lower dopaminergic functioning found in cannabis users.

OBJECTIVES

To investigate whether spatiotemporal contrast sensitivity and motion discrimination under normal and low luminance conditions differ in cannabis users and non-users.

METHODS

Control (n = 20) and cannabis (n = 21) participants completed a visual acuity test, a saliva test and self-report measures. Spatial and temporal contrast thresholds, motion coherence thresholds for translational and radial motion and the spontaneous eye blink rate were then collected.

RESULTS

Cannabis users showed decreased spatial contrast sensitivity under low luminance conditions and increased motion coherence thresholds under all luminance levels tested compared to non-users. No differences in temporal contrast sensitivity were found between the groups. Frequency of cannabis use correlated significantly and negatively with contrast sensitivity, both spatial and temporal, in the cannabis group and higher motion coherence thresholds for radial motion were also associated with more frequent cannabis use in this group. The eye blink rate was significantly lower in cannabis users compared to non-users.

CONCLUSIONS

The present study shows that cannabis use is associated with deficits in low level visual processing. Such deficits are suggested to relate to lower dopamine, in a similar manner as in clinical populations. The implications for driving safety under reduced visibility (e.g. night) in abstaining cannabis users are discussed.

Spatial attention and reading ability: ERP correlates of flanker and cue-size effects in good and poor adult phonological decoders

To investigate facilitatory and inhibitory processes during selective attention among adults with good (n=17) and poor (n=14) phonological decoding skills, a go/nogo flanker task was completed while EEG was recorded. Participants responded to a middle target letter flanked by compatible or incompatible flankers. The target was surrounded by a small or large circular cue which was presented simultaneously or 500ms prior. Poor decoders showed a greater RT cost for incompatible stimuli preceded by large cues and less RT benefit for compatible stimuli. Poor decoders also showed reduced modulation of ERPs by cue-size at left hemisphere posterior sites (N1) and by flanker compatibility at right hemisphere posterior sites (N1) and frontal sites (N2), consistent with processing differences in fronto-parietal attention networks. These findings have potential implications for understanding the relationship between spatial attention and phonological decoding in dyslexia.

Energy drink ingredients. Contribution of caffeine and taurine to performance outcomes

While the performance-enhancing effects of energy drinks are commonly attributed to caffeine, recent research has shown greater facilitation of performance post-consumption than typically expected from caffeine content alone. Consequently, the aim of the present study was to investigate the independent and combined effect of taurine and caffeine on behavioural performance, specifically reaction time. Using a double-blind, placebo-controlled, crossover, within-subjects design, female undergraduates (N=19) completed a visual oddball task and a stimulus degradation task 45min post-ingestion of capsules containing: (i) 80mg caffeine, (ii) 1000mg taurine, (iii) caffeine and taurine combined, and (iv) matched placebo. Participants completed each treatment condition, with sessions separated by a minimum 2-day washout period. Whereas no significant treatment effects were recorded for reaction time in the visual oddball task, facilitative caffeine effects were evident in the stimulus degradation task, with significantly faster reaction time in active relative to placebo caffeine conditions. Furthermore, there was a trend towards faster mean reaction time in the caffeine condition relative to the taurine condition and combined caffeine and taurine condition. Thus, treatment effects were task-dependent, in that independent caffeine administration exerted a positive effect on performance, and co-administration with taurine tended to attenuate the facilitative effects of caffeine in the stimulus degradation task only.

University Students' Views on the Nature of Science and Psychology

Students' understanding of the nature of science (NOS), and the degree to which they perceive their discipline to be part of science, are critical to their academic development in psychology. In Study 1, 650 first-year psychology students from three universities in Australia completed the Psychology as a Science (PAS) questionnaire, an adjective checklist relating to science and psychology, and the Science Knowledge and Attitudes (SKA) scale. Results confirmed the limited value of the PAS to identify components of the NOS, but indicated that students view psychology to be a science within a few weeks of the commencement of their study at university. Three factors underlying the SKA scale were identified: naïve view of science (NVS), social and cultural perspective (SCP), and knowledge of refutability (KR). In Study 2, 622 students at the University of Tasmania completed the SKA and items relating to their beliefs about studying. Scores on the three factors were correlated with beliefs about studying, scores on KR increased with years of study, and scores on NVS decreased with years of study. These data suggest that our educational practices do in fact lead to appropriate changes in students' NOS understanding in a manner consistent with the learning outcomes underpinning psychology graduate attributes.

Xenon Hexafluoride: Preparation of Pure Form and Melting Point

Xenon hexafluoride forms an addition compound with sodium fluoride which can be used to separate it from the other xenon fluorides and oxyfluoride. The melting point of pure xenon hexafluoride prepared in this way was 47.7 +/- 0.2 degrees C.

Electrophysiological indices of spatial attention during global/local processing in good and poor phonological decoders

Previous research suggests a relationship between spatial attention and phonological decoding in developmental dyslexia. The aim of this study was to examine differences between good and poor phonological decoders in the allocation of spatial attention to global and local levels of hierarchical stimuli. A further aim was to investigate the relationship between global/local processing and electrophysiological indices (N1, N2) of spatial attention in these groups. Good (n=18) and poor (n=16) phonological decoders were selected on the basis of non-word reading ability. Participants responded to either the global or local level of hierarchical stimuli presented in the left or right visual field in a sustained attention task. Poor phonological decoders showed slower RT relative to good phonological decoders regardless of whether attention was directed to either global or local processing levels. This was accompanied by a lack of task-related modulation of the posterior N1 and N2 Event-Related Potential (ERP) components, suggesting differences in the early allocation of spatial attention and later perceptual processing respectively. Poor decoders also showed greater N2 amplitude overall, suggestive of compensatory processing at later perceptual stages. There was preliminary evidence for sex differences in hemispheric lateralisation, with a reversal of hemispheric lateralisation observed among male and female poor phonological decoders. These findings have important implications for the understanding of the relationship between spatial attention and phonological decoding in developmental dyslexia.

The behavioural and electrophysiological effects of visual task difficulty and bimanual coordination mode during dual-task performance

The difficulty of a visual three stimulus and a bimanual coordination task was manipulated by varying discrimination difficulty (easy, hard) and coordination mode (in-phase, anti-phase) respectively. Electroencephalographic activity was recorded from 32 sites whilst participants (n = 16) completed four dual-task conditions in counterbalanced order. Longer reaction time and lower accuracy were found for the hard relative to the easy visual task and, for the hard visual task, accuracy was lower under anti-phase relative to in-phase conditions. Amplitude and latency of event-related potential components P3a and P3b were recorded and measured. There was a reduction in P3b amplitude and increase in P3a amplitude for the hard visual task overall and a further reduction in frontal P3b amplitude under the more demanding anti-phase condition. For the easy visual task, however, P3b and P3a amplitude were greater under the anti-phase relative to in-phase coordination condition at left hemisphere frontal sites. These findings suggest that the attentional cost of stabilising anti-phase bimanual coordination is largely associated with top-down automatic processes subserved by the frontal attentional network.

Event-related brain potentials elicited during word recognition by adult good and poor phonological decoders

Cognitive processing of lexical and sub-lexical stimuli was compared for good and poor adult phonological decoders. Sixteen good decoders and 16 poor decoders, average age 19 years, silently read 150 randomly computer presented sentences ending in incongruous regular, irregular, or nonwords and 100 congruent filler sentences. Electro-encephalographic recordings were made from the final word of each incongruous sentence. Although no significant group differences were found, good decoders showed specialised hemispheric word recognition processing at P200 and P300. Nonwords elicited greater N200 and P300 amplitudes for both good and poor decoders. Larger amplitude P200s were elicited by poor decoders when processing nonwords. These findings provide evidence for separable lexical and sub-lexical procedures and support a psychophysiological basis for a core phonological deficit in poor phonological decoders.

Combined effects of alcohol and caffeine on the late components of the event-related potential and on reaction time

The effects of .7 ml/kg alcohol and 200 mg caffeine on the P200, N200, P300 and N500 difference wave components of the event-related potential and on reaction time (RT) were examined in 16 females who performed both simple and choice RT tasks. Alcohol slowed the decision time (DT) component of reaction time, lengthened the latency of the P200 and P300 components, reduced N200 amplitude, increased P300 amplitude at parietal sites, and modified the effect of sagittal site on N500 difference wave peak amplitude. Caffeine shortened DT in the choice RT task, shortened N200 latency at right hemisphere sites, and shortened N200 latency in the choice RT task in combination with alcohol compared to when alcohol was administered alone. Caffeine also increased P300 amplitude in the choice RT task and reduced the integral of the N500 difference wave at most sites when combined with alcohol. It was concluded that whereas alcohol slows attention allocation and impairs working memory, caffeine accelerated response-related decisions and enhanced cortical arousal.

The interactive effects of alcohol and temazepam on P300 and reaction time

The present research investigated the separate and interactive effects of the minor tranquilizer, temazepam, and a low dose of alcohol on the amplitude and latency of P300 and on reaction time. Twenty-four participants completed four drug treatments in a repeated measures design. The four drug treatments, organised as a fully repeated 2 x 2 design, included a placebo condition, an alcohol only condition, a temazepam only condition, and an alcohol and temazepam combined condition. Event-related potentials were recorded from midline sites Fz, Cz, and Pz within an oddball paradigm. The results indicated that temazepam, with or without the presence of alcohol, reduced P300 amplitude. Alcohol, on the other hand, with or without the presence of temazepam, affected processing speed and stimulus evaluation as indexed by reaction time and P300 latency. At the low dose levels used in this experiment alcohol and temazepam appear not to interact, which suggests that they affect different aspects of processing in the central nervous system.

Structure and expression of a novel member, FGF-16, on the fibroblast growth factor family

We have isolated cDNA encoding a novel member (207 amino acids) of the FGF family from the rat heart by homology-based polymerase chain reaction. As this protein is the 16th documented member of the FGF family, we tentatively term it FGF-16. Among FGF family members, FGF-16 is most similar (73% amino acid identity) to FGF-9. We have also determined the structure of human FGF-16 with high amino acid sequence identity (98.6%) to rat FGF-16. Although the predicted FGF-16 amino acid sequence lacks a typical signal sequence, recombinant rat FGF-16 was efficiently secreted by Sf9 insect cells infected with recombinant baculovirus containing the cDNA. FGF-16 mRNA was predominantly expressed in the rat heart among the adult major tissues examined. The expression profile of FGF-16 mRNA was quite different from those of other members of the FGF family. In rat embryos, FGF-16 mRNA was predominantly expressed in the brown adipose tissue. However, the expression decreased greatly after birth. These results indicate that FGF-16 in embryos might play a role in development of the brown adipose tissue.

Identification of a potential role for the adventitia in vascular lesion formation after balloon overstretch injury of porcine coronary arteries

BACKGROUND

In the present series of experiments, we examined the onset of cell proliferation and growth factor expression after balloon overstretch injury to porcine coronary arteries.

METHODS AND RESULTS

Domestic juvenile swine underwent balloon overstretch injury to the left anterior descending and circumflex coronary arteries with standard percutaneous transluminal coronary angioplasty balloon catheters. To identify proliferating cells, 5-bromo-2-deoxyuridine (BrDU) was administered over a period of 24 hours before the animals were killed at either 1, 3, 7, or 14 days after injury. Immunohistochemistry was performed with monoclonal antibodies to BrDU and smooth muscle cell markers. Three days after injury, a large number of proliferating cells were located in the adventitia, with significantly fewer positive cells found in the media and lumen. Seven days after injury, proliferating cells were found primarily in the neointima, extending along the luminal surface. In situ hybridization for PDGF A-chain and beta-receptor mRNAs revealed that the expression of these two genes was closely correlated with the sites of proliferation at each time point. Studies in which BrDU was injected between days 2 and 3 and the animals were killed on day 14 suggested that the proliferating adventitial cells may migrate into the neointima.

CONCLUSIONS

These data suggest that adventitial myofibroblasts contribute to the process of vascular lesion formation by proliferating, synthesizing growth factors, and possibly migrating into the neointima. Increased synthesis of alpha-smooth muscle actin observed in the adventitial cells after arterial injury may constrict the injured vessel and contribute to the process of arterial remodeling and late lumen loss after angioplasty.

Avian stem cell factor (SCF): production and characterization of the recombinant His-tagged SCF of chicken and its neutralizing antibody

Recombinant chicken stem cell factor (SCF) was produced in bacteria as a histidine-tagged protein (His delta SCF) and purified by affinity chromatography on an Ni(2+)-NTA agarose column. His delta SCF is devoid of signal peptide and transmembrane domains and therefore mimics a soluble form of SCF. We demonstrate that the factor is biologically fully active in supporting sustained proliferation of SCF-dependent red blood progenitor cells of chicken in vitro. Polyclonal SCF-specific antibodies were raised in rabbits and shown to display potent SCF-neutralizing activity. Thus, recombinant chicken His delta SCF together with the SCF-specific antibody provide valuable tools for studying the role of SCF and c-kit receptor in development, growth and differentiation of avian haematopoietic cells.

Stem cell factor production by human marrow stromal fibroblasts

To characterize the production of stem cell factor (SCF, the ligand for the c-kit receptor protein) and its regulation by inflammatory cytokines and glucocorticoids, primary marrow stromal fibroblasts were isolated from normal individuals and two patients with Diamond-Blackfan anemia. Unstimulated normal marrow stromal fibroblasts constitutively expressed a low level of SCF mRNA (9 +/- 2 copies/cell [mean +/- SEM]), continually secreted soluble SCF into the supernatant of 1- to 5-day-old cultures (0.16 +/- 0.02 to 0.73 +/- 0.04 ng/mL per 10(6) cells, respectively), and expressed membrane-bound SCF. Stimulation with interleukin-1 beta (IL-1 beta) only modestly increased SCF mRNA levels, soluble SCF production at 24 hours, and membrane-bound SCF. In comparison, hydrocortisone or tumor necrosis factor alpha (TNF-alpha) exposure increased SCF mRNA levels 3.5- to four-fold above controls, but with different kinetics. The peak TNF-alpha effect was at 6 hours, with return to near control levels at 24 hours, whereas hydrocortisone induced maximal mRNA increases at 12 to 18 hours, and the levels remained high at 24 hours. Similarly, a sustained increase in soluble SCF production was detected during 1 to 5 days of hydrocortisone exposure (0.27 +/- 0.03 to 1.10 +/- 0.08 ng/mL per 10(6) cells), while TNF-alpha stimulation modestly increased the production of soluble SCF in 24-hour cultures only. Unstimulated normal marrow fibroblasts expressed predominantly the long species of alternatively spliced SCF mRNA, and the relative amounts of long and short mRNAs did not change after stimulation with IL-1 beta, hydrocortisone, or TNF-alpha. SCF production by marrow stromal fibroblasts from a symptomatic patient with Diamond-Blackfan anemia was equivalent to simultaneously studied normal marrow fibroblasts. In contrast, marrow fibroblasts from a Diamond-Blackfan anemia patient in untreated hematologic remission constitutively expressed high levels of SCF mRNA (21 +/- 4 copies/cell) and soluble protein (0.40 ng/mL per 10(6) cells at 24 hours). Together, these observations suggest that SCF is constitutively produced by fibroblasts in the human marrow microenvironment and that hydrocortisone induces a modest but sustained increase in SCF gene expression and protein production, compared to only a transient increase induced by TNF-alpha. In addition, these findings support the hypothesis that endogenous or corticosteroid-induced increases in the production of SCF could play a physiologic role in the clinical improvement of congenital anemia.

Steel and c-kit in the development of avian melanocytes: a study of normally pigmented birds and of the hyperpigmented mutant silky fowl

We describe here the expression of c-kit and Steel (Sl) genes during the development of melanocytes in normally pigmented strains of chick and quail compared to unpigmented (White Leghorn) and hyperpigmented (Silky Fowl) strains of chickens. By using the quail/chick chimera system, we found that the neural crest cells, which migrate dorso-laterally in the subectodermal mesenchyme to give rise to the melanocytes, express c-kit as early as E4, that is about 2 days after they have left the neural primordium. The Sl gene is expressed from E4 onward in the epidermis but not at all in the dermis at any developmental stage. As feather buds develop, Sl mRNA becomes restricted to the apical region of the feather filaments. During formation of the barbs and barbules of the down feather, production of the Steel factor is restricted to the external epidermal cells of the barbules. The cell bodies of the c-kit-positive melanocytes are then located in the internal border of the epidermal ridges and extend their processes toward the source of the Steel factor. We propose that the spatial restriction of Sl gene activity at that stage accounts for the morphology of the melanocytes and their vectorial secretion of melanin to the external barbule cells. As a whole, these results show that during skin development c-kit positive cells are present in the Steel factor-producing areas at the time when melanoblasts proliferate and differentiate. Interestingly, in the mouse, previous studies showed that the Sl gene is activated in the dermis where melanoblasts undergo most of their expansion (Nishikawa et al. [1991] EMBO J. 10:2111-2118). In the unpigmented and hyperpigmented mutants that we studied, expression of the Sl message, as judged quantitatively in Northern blots (for the SF embryos) or spatially by in situ hybridization, is similar to that observed in normal birds. In SF embryos the c-kit expressing melanoblasts migrate initially in the dorso-lateral migration pathway as in normal birds. However their number increases considerably in the dermis from E5 onward. From E7, they invade mesodermally derived organs that do not express the Sl gene. This suggests that another, still unknown, factor(s) is responsible for the survival, the proliferation, and the extensive spreading of melanocytic cells within the mesoderm of this mutant.

Effect of the Steel gene product on melanogenesis in avian neural crest cell cultures

Mutations at the Steel (Sl) and dominant white spotting (W) loci affect three embryonic lineages: primordial germ cells, hemopoietic stem cells and neural-crest-derived melanocytes. The gene products of these loci are a peptide growth factor, called here stem cell factor (SCF), and its tyrosine kinase receptor, the proto-oncogene c-kit. We have studied how chicken recombinant SCF affects the development of melanocytes from quail neural crest cells in secondary culture under defined conditions. We observed that the total number of neural crest cells, of melanocytes and of their precursors was higher in the presence than in the absence of SCF. Labelling with bromodeoxyuridine showed that SCF had a modest and transient mitogenic effect on the neural crest population. SCF also enhanced the differentiation rate of melanocyte precursors, recognized by the "melanocyte early marker" monoclonal antibody (MelEM MAb), and of melanocytes, since the proportion of both subpopulations significantly increased in the presence of SCF. Finally, SCF increased the survival of the neural crest population since in its presence the total number of cells remained stable while it gradually declined in control cultures. Our results support the notion that SCF sustains the survival of the neural crest population and stimulates the rate of the melanogenic differentiation process.

Canine stem cell factor (c-kit ligand) supports the survival of hematopoietic progenitors in long-term canine marrow culture

The cDNA for canine stem cell factor (cSCF, c-kit ligand) was cloned and expressed in Escherichia coli. The recombinant protein (rcSCF), 165 amino acids in length, is very similar structurally to the soluble form of previously cloned and sequenced rodent and human SCFs. The biological effects of rcSCF were studied in a day-10 granulocyte-macrophage colony-forming unit (CFU-GM) clonogenic assay and in long-term liquid bone marrow culture of non-adherent hematopoietic cells in the absence of a stromal underlayer. Synergism in the stimulation of growth of CFU-GM was demonstrated between rcSCF and both recombinant human (rh) granulocyte-macrophage colony-stimulating factor (GM-CSF) and naturally occurring colony-stimulating activity present in the serum of a neutropenic dog. Alone, rcSCF was nonstimulatory for committed marrow precursors in methylcellulose cultures and had minimal effect on hematopoietic progenitor cell survival in stromaless, liquid cultures. When rcSCF was combined with phytohemagglutinin-stimulated canine lymphocyte-conditioned medium (PHA-LCM) or rh interleukin 6 (IL-6), with or without rhGM-CSF, CFU-GM survived for up to 5 weeks. The combination of rcSCF and rhGM-CSF, without rhIL-6, led to an early increase in CFU-GM in liquid cultures that declined more rapidly than in flasks that included rhIL-6. Survival of progenitor cells was negligible beyond 1 week in flasks with growth factor combinations lacking rcSCF. Sustained production of nonadherent cells in long-term cultures also was dependent on rcSCF in combination with canine PHA-LCM or recombinant human growth factors. It appears that rcSCF, like that from rodent and primate species, has the ability to influence the survival and proliferation of CFU-GM, and perhaps earlier progenitor cells, in hematopoietic tissues. In a long-term liquid culture system in which growth factor production by stromal cells is limited, rcSCF possesses a unique ability to maintain the viability of progenitor cells for up to 5 weeks.

Support of human hematopoiesis in long-term bone marrow cultures by murine stromal cells selectively expressing the membrane-bound and secreted forms of the human homolog of the steel gene product, stem cell factor

The maintenance and differentiation of hematopoietic stem cells is influenced by cells making up the hematopoietic microenvironment (HM), including bone marrow-derived stromal cells. We and several other investigators have recently demonstrated the molecular basis of abnormal HM observed in the steel mutant mouse and cloned the normal cDNA products of this gene (termed SCF, KL, or MCF). In this report, we focus on the human counterpart of the mouse Steel (Sl) gene. Alternative splicing of the human SCF pre-mRNA transcript results in secreted and membrane-bound forms of the protein. To investigate the role of these two forms of human SCF, we targeted an immortalized stromal cell line derived from fetal murine homozygous (Sl/Sl) SCF-deficient embryos for gene transfer of various human cDNAs encoding SCF. We report that stable stromal cell transfectants can differentially process the two forms of human SCF protein product. We also demonstrate that both soluble SCF and membrane-bound SCF are active in increasing the number of human progenitor cells in the context of stromal cell cultures, although in a qualitatively different manner. Hence, the membrane-bound form of SCF may play an important role in the cell-cell interactions observed between stromal and hematopoietic cells both in vitro and in vivo.

Absence of abnormalities of c-kit or its ligand in two patients with Diamond-Blackfan anemia

As Diamond-Blackfan anemia shares clinical features with W and Steel defects in mice, we investigated the possibility that this human disorder might result from an abnormality of the c-kit receptor or its ligand, stem cell factor (SCF). For these studies, full nucleotide sequences for coding regions of c-kit and SCF were generated for two Diamond-Blackfan anemia patients and were normal. Similarly, the kds of SCF receptors on their marrow cells (31 pmol/L, 43 pmol/L) were comparable with those found in three normal controls (50 pmol/L, 55 pmol/L, 27 pmol/L). Serum SCF concentrations were 6.9 ng/mL in patient A, 14.6 ng/mL in patient B, who has been in hematologic remission since adolescence, and 2.7 ng/mL in the 3-year-old daughter of patient B, who also has Diamond-Blackfan anemia but is transfusion-dependent. It is possible that the SCF level in patient B increased with puberty, leading to her remission. These data provide evidence that Diamond-Blackfan anemia does not result from structural abnormalities of c-kit or SCF.

Diamond-blackfan anemia: in vitro response of erythroid progenitors to the ligand for c-kit

To provide insights into the pathogenesis of Diamond-Blackfan anemia, we examined the in vitro response of erythroid progenitors to the recently isolated ligand for c-kit (stem cell factor, SCF). For these studies, marrow or blood mononuclear cells from 10 Diamond-Blackfan patients were cultured with erythropoietin (Ep), Ep and interleukin-3, Ep and granulocyte-macrophage colony-stimulating factor, or Ep and lymphocyte conditioned media (LCM). These combinations were tested in the presence or absence of SCF. The mean number of cells per erythroid burst increased 5 to 50-fold in cultures containing SCF. Furthermore, many additional erythroid bursts were seen (mean increment 3.2 x baseline values). Although burst-forming unit-erythroid (BFU-E) from all patients responded, there were differences among individuals in the sensitivity of their BFU-E to SCF. In six patients and all control studies, plateau frequencies of erythroid bursts were achieved with less than or equal to 10 ng/mL SCF, whereas in studies from the other four patients, over 50 ng/mL SCF was required. These data invite speculation that the c-kit receptor/ligand axis is involved in the pathogenesis of Diamond-Blackfan anemia. More importantly and regardless of whether the observed patterns of response reflect the primary defect or an epiphenomenon, our data strongly support a therapeutic trial of SCF in patients with Diamond-Blackfan anemia.

Platelet factor 4 mRNA expression in human erythroleukemic cells: regulation by phorbol esters and certain cytokines

Developing megakaryocytes are distinguished from progenitor cells by the appearance of platelet proteins such as platelet factor 4 (PF 4). The human erythroleukemic cell line HEL can also be induced to produce PF 4 by incubation in phorbol esters. HEL cells were used here as a model system in which to study the phenomenon of inducible PF 4 production at both the mRNA and protein levels. The cytokines interleukin 1 beta (IL-1 beta), interleukin 3 (IL-3), interleukin 6 (IL-6), granulocyte-macrophage colony-stimulating factor (GM-CSF), erythropoietin (EPO), and transforming growth factor-beta (TGF-beta) were also evaluated for their effects on PF 4 mRNA induction in HEL cells.

Stem cell factor (SCF), a novel hematopoietic growth factor and ligand for c-kit tyrosine kinase receptor, maps on human chromosome 12 between 12q14.3 and 12qter

Recently a novel hematopoietic growth factor, stem cell factor (SCF), was cloned and demonstrated to be the ligand for the c-kit tyrosine kinase receptor. In the mouse, SCF is encoded by Sl (steel), a gene critical to the development of several distinct cell lineages during embryonic life and which has important effects on hematopoiesis in the adult animal. The Sl/SCF locus maps to the distal region of mouse chromosome 10, in the vicinity of genes that have been mapped to human chromosome 12. Here we report the use of somatic cell hybrid lines to localize SCF to the long arm of human chromosome 12, between 12q14.3 and 12qter. In addition to localizing the Sl homolog in man, these data provide further evidence for the conservation of synteny between the long arm of human chromosome 12 and the distal end of mouse chromosome 10.

Stem cell factor is encoded at the Sl locus of the mouse and is the ligand for the c-kit tyrosine kinase receptor

We have cloned a partial cDNA encoding murine stem cell factor (SCF) and show that the gene is syntenic with the Sl locus on mouse chromosome 10. Using retroviral vectors to immortalize fetal liver stromal cell lines from mice harboring lethal mutations at the Sl locus (Sl/Sl), we have shown that SCF genomic sequences are deleted in these lines. Furthermore, two other mutations at Sl, Sld and Sl12H, are associated with deletions or alterations of SCF genomic sequences. In vivo administration of SCF can reverse the macrocytic anemia and locally repair the mast cell deficiency of Sl/Sld mice. We have also provided biological and physical evidence that SCF is a ligand for the c-kit receptor.

Primary structure and functional expression of rat and human stem cell factor DNAs

Partial cDNA and genomic clones of rat stem cell factor (SCF) have been isolated. Using probes based on the rat sequence, partial and full-length cDNA and genomic clones of human SCF have been isolated. Based on the primary structure of the 164 amino acid protein purified from BRL-3A cells, truncated forms of the rat and human proteins have been expressed in E. coli and mammalian cells and have been shown to possess biological activity. SCF is able to augment the proliferation of both myeloid and lymphoid hematopoietic progenitors in bone marrow cultures. SCF exhibits potent synergistic activities in conjunction with colony-stimulating factors, resulting in increased colony numbers and colony size.

Base pairing involving deoxyinosine: implications for probe design

The thermal stability of oligodeoxyribonucleotide duplexes containing deoxyinosine (I) residues matched with each of the four normal DNA bases were determined by optical melting techniques. The duplexes containing at least one I were obtained by mixing equimolar amounts of an oligonucleotide of sequence dCA3XA3G with one of sequence dCT3YT3G where X and Y were A, C, G, T, or I. Comparison of optical melting curves yielded relative stabilities for the I-containing standard base pairs in an otherwise identical base-pair sequence. I:C pairs were found to be less stable than A:T pairs in these duplexes. Large neighboring-base effects upon stability were observed. For example, when (X,Y) = (I,A), the duplex is eight-fold more stable than when (X,Y) = (A,I). Independent of sequence effects the order of stabilities is: I:C greater than I:A greater than I:T congruent to I:G. This order differs from that of deoxyguanosine which pairs less strongly with dA; otherwise each deoxyinosine base pair is less stable than its deoxyguanosine counterpart in the same sequence environment. Implications of these results for design of DNA oligonucleotide probes are discussed.

Base-base mismatches. Thermodynamics of double helix formation for dCA3XA3G + dCT3YT3G (X, Y = A,C,G,T)

Thermodynamic parameters for double strand formation have been measured for the sixteen double helices of the sequence dCA3XA3G.dCT3YT3G, with each of the bases A, C, G and T at the positions labelled X and Y. The results are analyzed in terms of nearest-neighbors and are compared with thermodynamic parameters for RNA secondary structure. At room temperature the sequence (Formula: see text) is more stable than (Formula: see text) and is similar in stability to (Formula: see text) and (Formula: see text) are least stable. At higher temperatures the sequences containing a G.C base pair become more stable than those containing only A.T. All molecules containing mismatches are destabilized with respect to those with only Watson-Crick pairing, but there is a wide range of destabilization. At room temperature the most stable mismatches are those containing guanine (G.T, G.G, G.A); the least stable contain cytosine (C.A, C.C). At higher temperatures pyrimidine-pyrimidine mismatches become the least stable.

Comparative study of ribonucleotide, deoxyribonucleotide, and hybrid oligonucleotide helices by nuclear magnetic resonance

The nonexchangeable base protons and the hydrogen-bonding NH--N imino protons were used to study the conformations and the helix--coil transitions in the following oligonucleotides: (I) dCT5G + dCA5G, (II) rCU5G + rCA5G, (III) dCT5 G + rCA5G, (IV) rCU5G + dCA5G. The first three mixtures all form stable double-helical structures at 5 degrees C, whereas IV forms a triple strand with an rCU5G:dCA5G 2:1 ratio. The chemical shifts of the imino protons in the double strands indicate that I, II, and III have different conformations in solution. For example, the hydrogen-bonded proton of one of the C.G base pairs is more deshielded (a 0.4-ppm downfield shift) in helix I than in helix II or III. This implies a significant change in helical parameters, such as the winding angle, the distance between base pairs, or overlap of the bases. The coupling constants of the H1' sugar protons show that helix I has 90% 2'-endo sugar conformation, whereas helix III has greater than 85% 3'-endo conformation for the observed sugar rings. The sugar pucker data are consistent with helix I having B-family geometry; III has A-family geometry. The chemical shifts of the nonexchangeable base protons in system I were followed with increasing temperature. The midpoints for the transitions, Tm's, for all the base protons were 28--30 degrees C; this indicates an all-or-none transition.

DNA-RNA hybrid duplexes containing oligo(dA:rU) sequences are exceptionally unstable and may facilitate termination of transcription

A DNA-RNA hybrid oligonucleotide duplex, dC(pA) 5pG:rC(pU)5pG, which contains a (dA:rU) 5 sequence, is at least 200 times less stable at room temperature than the corresponding duplex containing an (rA:dT) 5 sequence, rC(pA)5pG:dC(pT)5pG. This result provides an explanation for the finding that most primary RNA transcripts terminate in several consecutive rU residues, but not rA residues. It strongly supports the idea that instability of the DNA-RNA hybrid at the growing point of transcription plays a role in termination of transcription.

Fatal pulmonary hypertension and resolving immune-complex glomerulonephritis in mixed connective tissue disease. A case report and review of the literature

Mixed connective tissue disease (MCTD) has been characterized as a benign rheumatic syndrome with a favorable response to immunosuppressive therapy. Serious renal and pulmonary involvement are reported to be rare in MCTD. We are describing a female adolescent with MCTD in whom fatal cor pulmonale developed due to recurrent thromboembolic primary pulmonary hypertension. Death occurred after two years of therapy with prednisone and azathioprine for an immune-complex glomerulonephritis. Paramesangial and intramembranous electron-dense deposits had been identified in several glomeruli at the start of treatment. Improved renal function and apparent histologic improvement were demonstrated four months after the institution of prednisone and azathioprine therapy, and stable renal function was maintained until death. The pulmonary hypertension was progressive and apparently not altered by either the prednisone or azathioprine. At necropsy, there was no evidence of a pulmonary arteritis or vascular immune-complex deposition to account for the recurrent thromboembolic lesions in the small pulmonary arteries and arterioles. This is a clinical course not previously described in patients with MCTD and may represent an extreme of the clinical spectrum of this syndrome.

Bacterial endocarditis in subjects 60 years of age and older

Forty-two cases of bacterial endocarditis with pathologic confirmation are reviewed. Infection was restricted to one or both left-sided valves in 31 cases, right-sided valves in five cases, and valves in both sides of the heart in six cases. In those specimens available for review, underlying valvular disease was identifiable in 24 of 38 cases (63%). The common underlying diseases, in order of decreasing frequency, were calcified or otherwise deformed aortic valves (11 cases) and rheumatic fibrosis of the mitral valve (eight cases). The floppy mitral valve was the underlying condition in two cases and amyloid infiltration of the tricuspid valve in one. Among the 34 cases from which a specific organism was identified, the dominant organisms were Staphylococcus (14 cases) and various types of Streptococci(ten cases). Fungi were the causative organisms in two cases. The clinical suspicion for the presence of bacterial endocarditis was low (40% of 40 cases with adequate data). In those cases with adequate data, murmurs were present in 68% and fever in 93%. Of those patients with fever, clinical diagnosis was made or suspected in only 38%. When a murmur was present, the clinical diagnosis was made or suspected in 54% of the cases, while when a murmur was absent the disease was suspected in only 9% of the cases. The clinical diagnosis of bacterial endocarditis in older subjects depends upon 1) knowledge that the disease may occur in such subjects and 2) recognition that, although fever is commonly present, murmurs may be absent.