Molecular modeling and experimental approaches toward designing a minimalist protein having Fc-binding activity of Staphylococcal protein A

Protein A (PA), a cell wall constituent of Staphylococcus aureus, has got the unique property of binding with the Fc fragment of IgG from various species. The sequence data indicate five highly homologous Fc-binding regions in protein A. Computer sequence analysis provided the tryptic and chymotryptic fragments of IgG-binding domains of protein A. Molecular modeling in conjunction with molecular mechanical calculation has been used to search for the smallest possible proteolytic fragments of PA, still retaining Fc-binding activity. A 20-residue peptide (typtic fragment) and a 16-residue peptide (chymotryptic fragment) have been indicated, by molecular modeling studies, to possess IgG-binding affinity comparable to that of the B domain of Protein A. Binding of a 20-residue peptide has been substantiated experimentally by immunoprecipitation, capillary electrophoresis, and circular dichroism spectroscopic analyses.

S. aureus superantigen protein A expands CD4(+)/CD8(+)/CD19(+)/CD34(+) cells in mice: a potential immunorestorer

Protein A (PA) of Staphylococcus aureus is known for its immunostimulatory, anti-cancer, and anti-toxic properties. The present study revealed that PA stimulates specific immunocytes to act as a potential immunorestorer. It has also been shown that the percentage of various cell types bearing different clusters of differentiation markers, e.g., CD4(+), CD8(+), CD19(+), increases considerably after inoculation with PA. It has also been observed that CD34(+) progenitor cells of bone marrow also increased significantly (P < 0.05) upon PA treatment. PA significantly elevated Th-1 cytokines, e.g., IFN-gamma, TNF-alpha, and IL-1alpha. The increased percentages of CD4(+), CD8(+), CD19(+), CD34(+) cells and elevated cytokine levels in PA treated animals may contribute to the reported anti-tumor, anti-fungal, anti-parasitic, and anti-toxic properties of PA. Since in various diseased conditions and during toxic drug therapy lymphocytes bearing such differentiation markers get suppressed, this type of approach could help in immunorestoration of the host. These findings might help in designing therapeutic approaches toward various diseases which cause immunosuppression.

Isoenzyme and molecular characterization of Entamoeba histolytica and Entamoeba dispar isolates from symptomatic and asymptomatic subjects

AIM

To correlate the clinical features of amebic infections with the characteristics of Entamoeba culture isolates of stools.

METHODS

Isolates from seven irritable bowel syndrome (IBS) patients, four asymptomatic cyst passers (ACP) and five patients with invasive amebic disease were subjected to hexokinase polyacrylamide electrophoresis (HK-PAGE) and their DNA subjected to restriction fragment (RF) analysis of amplified polymerase chain reaction (PCR) products. These findings were correlated with anti-amebic serology. Two axenic pathogenic strains (HM1:IMSS, NIH:200) and one xenic nonpathogenic strain (SAW1734) were used as standards.

RESULTS

All isolates from IBS patients as well as ACP had slow-moving (nonpathogenic) band pattern, whereas those from patients with invasive disease had fast-moving (pathogenic) band pattern on HK-PAGE. Serological data using EIA and RF patterns of PCR-amplified genome corroborated these results.

CONCLUSIONS

Our results support the view that there are two species of Entamoeba infecting humans--E. histolytica(pathogenic) and E. dispar (nonpathogenic), and HK-PAGE of culture isolates can differentiate between them.

Rapid detection of elevated prostate-specific antigen levels in blood: performance of various membrane strip tests compared

OBJECTIVES

To compare the ability of four commercially available membrane strip tests to detect increased (4 microg/L or more) concentrations of prostate-specific antigen (PSA) in blood.

METHODS

Serum samples with PSA concentrations less than 4 microg/L (n = 67) and from greater than 4 microg/L to 20 microg/L (n = 32) were independently examined by two observers using the PSA membrane strip tests from Chembio, Medpro, Seratec, and Syntron. The positive and negative results of each membrane strip test were classified as either true positive or negative and false negative or positive by comparing them with the quantitative PSA assay of Immulite DPC using the conventional threshold value of 4 microg/L.

RESULTS

The interobserver variations of the tests were between 93% and 97%. The color stability of the Seratec and Chembio tests did not show significant differences between test results read within 10 to 20 minutes of the reaction time; however, the results of the other two tests were especially affected by variations in the reading time. The sensitivity and specificity of the tests in relation to the threshold of 4 microg/L were 67% to 93% and 87% to 97%, respectively.

CONCLUSIONS

The Syntron test and, within certain limitations, the Seratec test fulfill the concept of a rapid and convenient PSA determination to detect PSA concentrations greater than 4 microg/L. Methodologic optimization of the tests by a grading of the PSA measuring ranges (eg, between 0 and 2, 3 and 4, 4 and 6, and 7 and 10 microg/L) should be taken into account for future development.

MCM21 and MCM22, two novel genes of the yeast Saccharomyces cerevisiae are required for chromosome transmission

The minichromosome maintenance genes, MCM21 and MCM22, have been cloned and are shown to code for the ORFs YDR318W and YJR135C respectively. Mutations in these genes caused a decrease in the stability of the minichromosome. This decrease in stability was associated with an increase in the copy number of the minichromosome in cells carrying it. Small circular dicentric plasmids were maintained relatively stably and structurally intact in the mutants compared with the wild-type strain. In the latter, such plasmids were mitotically unstable and, upon recovery, showed frequent rearrangements of their DNA. A centromere offered less obstruction to transcription in mutant cells than in the wild type, showing that both these mutants had a more relaxed kinetochore assembly. The mutant strains showed elevated rates of chromosome loss but not those of recombination. Both the mutations caused the cells to display a higher sensitivity towards the anti-mitotic drug benomyl. All these observations suggest that MCM21 and MCM22 are important for chromosome segregation with a potential role in kinetochore function. These genes are non-essential, as their deletions from chromosomes did not cause loss of cell viability. However, exponentially growing mutant cells carrying the deletion of the MCM21 gene had a significant population of large-budded cells with a single nucleus at the neck. Furthermore, the DNA content of these cells showed a shift towards 2N, suggesting a temporary pause of cells in G2 or in an early phase of mitosis. The mcm21 and mcm22 mutations do not show synthetic lethality or any further enhancement of growth defects, implying that they could be carrying out non-overlapping functions in chromosome segregation.

A symmetry perceiving adaptive neural network and facial image recognition

The paper deals with the forensic problem of comparing nearly from view and facial images for personal identification. The human recognition process for such problems, is primarily based on both holistic as well as feature-wise symmetry perception aided by subjective analysis for detecting ill-defined features. It has been attempted to approach the modelling of such a process by designing a robust symmetry perceiving adaptive neural network. The pair of images to be compared should be presented to the proposed neural network (NN) as source (input) and target images. The NN learns about the symmetry between the pair of images by analysing examples of associated feature pairs belonging to the source and the target images. In order to prepare a paired example of associated features for training purpose, when we select one particular feature on the source image as a unique pixel, we must associate it with the corresponding feature on the target image also. But, in practice, it is not always possible to fix the latter feature also as a unique pixel due to pictorial ambiguity. The robust or fault tolerant NN takes care of such a situation and allows fixing the associated target feature as a rectangular array of pixels, rather than fixing it as a unique pixel, which is pretty difficult to be done with certainty. From such a pair of sets of associated features, the NN searches out proper locations of the target features from the sets of ambiguous target features by a fuzzy analysis during its learning. If any of target features, searched out by the NN, lies outside the prespecified zone, the training of the NN is unsuccessful. This amounts to non-existence of symmetry between the pair of images and confirms non-identity. In case of a successful training, the NN gets adapted with appropriate symmetry relation between the pair of images and when the source image is input to the trained NN, it responds by outputting a processed source image which is superimposable over the target images and identity may subsequently be established by examining detailed matching in machine-made superimposed/composite images which are also suitable for presentation before the court. The performance of the proposed NN has been tested with various cases including simulated ones and it is hoped to serve as a working tool of forensic anthropologists.

Increased expression of annexin I and thioredoxin detected by two-dimensional gel electrophoresis of drug resistant human stomach cancer cells

The therapy of advanced cancer using chemotherapy alone or in combination with radiation or hyperthermia yields an overall response rate of about 20-50%. This success is often marred by the development of resistance to cytostatic drugs. Our aim was to study the global analysis of protein expression in the development of chemoresistance in vitro. We therefore used a cell culture model derived from the gastric carcinoma cell line EPG 85-257P. A classical multidrug-resistant subline EPG85-257RDB selected to daunorubicin and an atypical multidrug-resistant cell variant EPG85-257RNOV selected to mitoxantrone, were analysed using two-dimensional electrophoresis in immobilized pH-gradients (pH 4.0-8.0) in the first dimension and linear polyacrylamide gels (12%) in the second dimension. After staining with coomassie brilliant blue, image analysis was performed using the PDQuest system. Spots of interest were isolated using preparative two-dimensional electrophoresis and subjected to microsequencing. A total of 241 spots from the EPG85-257RDB-standard and 289 spots from the EPG85-257RNOV-standard could be matched to the EPG85-257P-standard. Microsequencing after enzymatic hydrolysis in gel, mass spectrometric data and sequencing of the peptides after their fractionation using microbore HPLC identified that two proteins annexin I and thioredoxin were overexpressed in chemoresistant cell lines. Annexin I was present in both the classical and the atypical multidrug-resistant cells. Thioredoxin was found to be overexpressed only in the atypical multidrug-resistant cell line.

The MCM16 gene of the yeast Saccharomyces cerevisiae is required for chromosome segregation

We have cloned and characterized the MCM16 gene required for the maintenance of minichromosomes in the yeast Saccharomyces cerevisiae. This gene corresponds to a 181-amino acid ORF, YPR046W, on chromosome XVI. Mutant cells carrying minichromosomes accumulate them in higher copy numbers than do wild-type cells. Intact dicentric plasmid could be recovered from the mutant, in contrast to the wild-type, in which the plasmid suffered frequent deletions. A wild-type centromere, CEN6, acts as a block to the transcription of a reporter gene, such as beta-galactosidase. This block was less effective in the mutant than in the wild-type strain, suggesting alterations in kinetochore assembly in the former. The mutant also showed increased sensitivity to the antimitotic drugs benomyl and thiabendazole. The mcm16 mutation caused a high rate of loss of chromosome III, without any significant increase in the recombination frequency. A strain carrying a deletion-disruption derivative of the MCM16 gene was viable and, when compared to the wild-type, did not show any significant changes in growth rate or cell morphology at 16, 23 and 37 degrees C. These properties show that MCM16 is required for an important but nonessential role that governs the kinetochore-microtubule mediated process of chromosome segregation.

Top-down influences on stereoscopic depth-perception

The interaction between depth perception and object recognition has important implications for the nature of mental object representations and models of hierarchical organization of visual processing. It is often believed that the computation of depth influences subsequent high-level object recognition processes, and that depth processing is an early vision task that is largely immune to 'top-down' object-specific influences, such as object recognition. Here we present experimental evidence that challenges both these assumptions in the specific context of stereoscopic depth-perception. We have found that observers' recognition of familiar dynamic three-dimensional (3D) objects is unaffected even when the objects' depth structure is scrambled, as long as their two-dimensional (2D) projections are unchanged. Furthermore, the observers seem perceptually unaware of the depth anomalies introduced by scrambling. We attribute the latter result to a top-down recognition-based influence whereby expectations about a familiar object's 3D structure override the true stereoscopic information.

Late clotted haemothorax after blunt chest trauma

A clotted haemothorax can develop any time after blunt chest trauma. Two cases are described in which late clotted haemothoraces developed which were treated by limited thoracotomy and evacuation of clots. Late clotted haemothorax may occur even in the absence of any abnormal initial clinical findings. Early detection and treatment is important to avoid the complications of fibrothorax and empyema with permanent pulmonary dysfunction. After blunt chest trauma patients should be advised to return to the accident and emergency department for assessment on development of any new chest symptom. Under these circumstances a chest x ray is mandatory to exclude a haemothorax.

Spaceflight influences on ocular counterrolling and other neurovestibular reactions

Exposure to extended periods of weightlessness in orbital flight has profound effects on the neurovestibular system and influences head and eye movements, postural control, and spatial orientation. The associated space motion sickness is among the earliest of the signs of adaptation to this new environment. This report both reviews the prominent neurovestibular phenomena associated with going into space and returning to earth and relates the issues to vestibular compensation and rehabilitation. New results from the Spacelab SLS-2 mission are included, showing significant reductions in postflight ocular counterrolling and changes in ocular counterrolling left/right asymmetries after 2 weeks in space.

Spaceflight Influences on Ocular Counterrolling and Other Neurovestibular Reactions

Exposure to extended periods of weightlessness in orbital flight has profound effects on the neurovestibular system and influences head and eye movements, postural control, and spatial orientation. The associated space motion sickness is among the earliest of the signs of adaptation to this new environment. This report both reviews the prominent neurovestibular phenomena associated with going into space and returning to earth and relates the issues to vestibular compensation and rehabilitation. New results from the Spacelab SLS-2 mission are included, showing significant reductions in postflight ocular counterrolling and changes in ocular counterrolling left/right asymmetries after 2 weeks in space. (Otolaryngol Head Neck Surg 1998;118:S31-S34.)

Contribution of early acute rejection episodes to chronic rejection in a rat kidney retransplantation model

Chronic graft rejection represents the single most important risk factor for unsatisfactory long-term results after organ transplantation. In addition to various alloantigen dependent and independent factors, acute rejection episodes have been cited as a major immunological risk factor. However, the effects of acute rejection episodes on long-term graft outcome remains unknown. To examine the influence of a single early rejection event on ultimate graft outcome, acutely rejecting rat kidney grafts were retransplanted sequentially into syngeneic rats and their functional and structural behavior assessed over time. LEWxBNF1 kidney allografts and LEW isografts were removed from their LEW recipients after three, four, five and seven days (N = 12/group/time period) and retransplanted into donor strain hosts. The grafts were followed functionally and harvested four, eight, and 32 weeks later. Urinary protein excretion was measured weekly. Kidneys were examined morphologically and immunohistologically using monoclonal antibodies (mAbs) against macrophages (ED-1), T cells and their subsets (CD5, CD4, CD8), MHC class II expression (OX3) and adhesion molecules (ICAM-1 and LFA-1alpha). The mean standard time +/- SD of non-retransplanted allografts was 14.5 +/- two days; isografts functioned indefinitely. At five and seven days, acutely rejecting allografts showed massive cellular infiltrates associated with extensive necrosis. These changes could not be reversed by retransplantation and the syngeneic recipients later died of renal failure. In contrast, most allografts retransplanted earlier in the process recovered completely when retransplanted after three (12 of 12 allografts) and four (7 of 12 allografts) days. During the subsequent follow-up period, urinary protein excretion was comparable in retransplanted allografts and isografts. The increased mononuclear cell infiltration in non-retransplanted allografts seen at three and four days was only occasionally observed during the follow-up period after retransplantation. Only a few sclerosed glomeruli (approximately 15%), mild arterial changes and minimal cellular infiltrates were observed by 32 weeks, which were similar to that seen in retransplanted isografts. A single acute rejection episode was completely reversible and did not progress to chronic rejection if retransplanted into syngeneic donors when the inflammatory changes are still early. Those results demonstrate the critical effect of alloantigen-dependent events on chronic graft deterioration, and indicate that prompt and aggressive treatment of initial acute rejection episodes are beneficial to protect against late deleterious changes in the graft.

Endometrial cancer thirteen years after total abdominal hysterectomy and bilateral salpingo-oophorectomy and hormone replacement therapy: a case report

We have reported a very interesting, rare case of endometrial adenocarcinoma arising from pelvic endometriosis thirteen years after hysterectomy with bilateral salpingo-oophorectomy, followed with hormone replacement therapy. Our patient presented with history of abnormal vaginal bleeding, which was investigated with abdominal scans, examination under anaesthesia (EUA), and biopsy. Histology of which confirmed malignant transformation. We then proceeded to primary excision of all macroscopic tumour and palpable lymph nodes followed with radiotherapy.

Evaluation of Internet-based oncologic teaching for medical students

BACKGROUND

Electronic tools with substantial educational applications are now widely available.

METHODS

In a prospective, randomized study, the value of Web-based educational tools for teaching second-year medical students was evaluated. The 35-hour, image-intensive multifaculty neoplasia course was selected for the experiment, with 103 students assigned to the control group (C) and 61 to the experimental group (E). Representative password-controlled multimedia course modules, accessible via the Internet, were developed. The E cohort was exposed to both classroom and Web-aided materials, whereas the C group had access to the Web modules only after the experiment was concluded (but before the final examination). Pre- and post-exposure questionnaires assessed computer knowledge, familiarity with the Internet, availability of computer access, and the value of Web-based education for both cohorts. Additionally, pre-and post-exposure tests were administered to both cohorts based on educational materials presented in the Web modules.

RESULTS

The overall participation rate was 64% (E = 69%; C = 60%). The post-test showed no major performance difference between the two groups. The questionnaires revealed that: less than 1% of the students had not accessed the Internet previously; less than 5% had not used the Internet for medical education before; 34% felt that computer resources on campus were inadequate; and over 75% found Web-based education to be an important additional educational resource. The major negative aspect was the slow pace of data transfer for modem-based home access. Only 1% of students felt that Web-based education could completely replace traditional teaching.

CONCLUSION

The potential for incorporating Web-based education in the medical curriculum is considerable.

Nitroglycerin to facilitate fetal extraction during cesarean delivery

OBJECTIVE

To determine the efficacy of nitroglycerin in easing fetal extraction in elective cesarean deliveries in comparison with placebo and to collect maternal and fetal pharmacologic data after administration of nitroglycerin.

METHODS

This randomized, double-blind clinical and descriptive pharmacokinetic study was carried out at the gynecology departments at Virchow Hospital and Charité Hospital (both university hospitals of Humboldt University, Berlin, Germany) between June 1994 and July 1996 in patients scheduled for elective cesarean delivery under general anesthesia. At the time of the uterine puncture incision, either 0.25 mg or 0.5 mg of nitroglycerin or a physiologic saline solution was administered as an intravenous bolus. Intraoperatively, maternal and neonatal pulse rates and blood pressure were monitored closely. The surgeons estimated reduction in uterine tone and the ease of fetal extraction by means of defined scales. Plasma concentrations of nitroglycerin and its metabolites were measured in maternal venous blood and from umbilical blood.

RESULTS

Ninety-seven patients were included in the statistical evaluation of the study; 32 received 0.25 mg of nitroglycerin, 34 received 0.5 mg of nitroglycerin, and 31 received placebo. The evaluation of the surgeons' estimation revealed no significant difference in ease of fetal extraction (statistical power 0.7) and no significant reduction in uterine tone under treatment with both nitroglycerin dosages in comparison with placebo. Only substance-specific maternal side effects were noted. The neonates' conditions were not affected by administration of nitroglycerin. The median fetal-maternal ratio of venous nitroglycerin plasma levels was approximately 1:400 in the 0.25-mg nitroglycerin group and 1:160 in the 0.5-mg nitroglycerin group. Approximately 11-12 times more nitroglycerin was detected in the venous umbilical branch than in the arterial branch.

CONCLUSION

Administration of nitroglycerin leads to no clinically relevant easing of fetal extraction, at least not in elective cesarean deliveries after the 34th week of gestation. With regard to pharmacokinetics, the measured median fetal-maternal venous nitroglycerin concentration was 1:400 in the 0.25-mg group and 1:160 in the 0.5-mg group.

Top-down learning of low-level vision tasks

Perceptual tasks such as edge detection, image segmentation, lightness computation and estimation of three-dimensional structure are considered to be low-level or mid-level vision problems and are traditionally approached in a bottom-up, generic and hard-wired way. An alternative to this would be to take a top-down, object-class-specific and example-based approach. In this paper, we present a simple computational model implementing the latter approach. The results generated by our model when tested on edge-detection and view-prediction tasks for three-dimensional objects are consistent with human perceptual expectations. The model's performance is highly tolerant to the problems of sensor noise and incomplete input image information. Results obtained with conventional bottom-up strategies show much less immunity to these problems. We interpret the encouraging performance of our computational model as evidence in support of the hypothesis that the human visual system may learn to perform supposedly low-level perceptual tasks in a top-down fashion.

The congested-like tracheae gene of Drosophila melanogaster encodes a member of the mitochondrial carrier family required for gas-filling of the tracheal system and expansion of the wings after eclosion

A recessive semi-lethal mutation resulting from the insertion of a P-lacW transposon at the cytological position 23A on the polytene chromosomes of Drosophila melanogaster was found to affect the unfolding and expansion of the wings resulting in a loss of venation and a marked decrease in their size. Lethality was polyphasic with numerous animals dying during early larval development and displaying apparently collapsed tracheal trees. The gene was therefore designated as congested-like tracheae, or colt. The colt mutation resulted from the insertion of a P-lacW transposon within the coding region of a 1.4-kb transcript. Wild-type function was restored by inducing a precise excision of the P-lacW transposon, while a deletion of the colt locus, produced by imprecise excision of the P element, showed a phenotype similar to that of the original P insert. The colt gene consists of a single exon and encodes a protein of 306 amino acids made of three tandem repeats, each characterized by two predicted transmembrane segments and a loop domain. The COLT protein shares extensive homology with proteins in the mitochondrial carrier family and particularly with the DIF-1 protein of Caenorhabditis elegans, which has been shown to be maternally required for embryonic tissue differentiation. Our analysis revealed that zygotic colt function is dispensable for normal embryonic morphogenesis but is required for gas-filling of the tracheal system at hatching time of the embryo and for normal epithelial morphogenesis of the wings.

Maternal adrenalectomy eliminates a surge of plasma dehydroepiandrosterone in the mother and attenuates the prenatal testosterone surge in the male fetus

Previous work has established a number of sex-related deficits in immune function, behavior, and endocrine responses to stress in the offspring of dams exposed to ethanol. To examine the potential role of maternal glucocorticoids as a mediator of these sexually dimorphic effects in the fetus, we examined the influence of prenatal alcohol exposure in the presence or absence of maternal glucocorticoids on fetal plasma corticosterone (CORT) production. An additional question to be addressed by these studies was whether maternal adrenalectomy could eliminate the known inhibition by ethanol of the prenatal surge of plasma testosterone in male fetuses. Pregnant dams were adrenalectomized (ADX) or sham-adrenalectomized on gestational day (G) 7 and placed on a liquid diet containing 35% ethanol-derived calories or pair-fed an isocaloric control diet throughout the experiment. On G18, G19, and G21, plasma levels of CORT, testosterone, and dehydroepiandrosterone (DHEA) were measured in male and female fetuses and their mothers. Ethanol administration consistently increased maternal plasma CORT levels but did not significantly alter CORT levels in the fetus. Maternal ADX resulted in compensatory increases in fetal CORT levels that were lower in fetuses of ADX dams on alcohol, suggesting a direct effect of ethanol on fetal pituitary-adrenal activity. There were no significant sex differences in fetal plasma CORT levels in response to any of these manipulations. A novel surge of maternal plasma DHEA was found on G19 that was absent in plasma from ADX dams. In spite of the absence of a surge on G19, plasma DHEA levels of ADX dams rose from very low levels at G18 to levels on G21 that were significantly higher than in Sham dams. A normal testosterone surge was observed in male fetuses on G18 and G19 from sham-adrenalectomized dams administered the pair-fed diet. However, this surge was greatly attenuated in males administered ethanol and also in male fetuses from ADX dams. These results reveal a direct inhibitory influence of ethanol on fetal CORT secretion as well as on the prenatal testosterone surge in males. Furthermore, these studies demonstrate the presence of a surge of DHEA in the pregnant rat. Overall, these data suggest that there is a critical adrenal factor in the rat that regulates the maternal surge of DHEA on G19 and the prenatal testosterone surge of male fetuses on G18-19.

Interferon-induced growth arrest is mediated by membrane structural changes

Interferon-gamma (IFN-gamma) is an immunomodulator shown to augment the expression of major histocompatibility (MHC) class I/class II antigens on the cell surface. In previous studies, we have demonstrated that the enhanced expression of these antigens on the cell surface is in part due to IFN-gamma-mediated abrogation of antigen shedding. In this study, we demonstrate that IFN-gamma induces structural changes in the cell membrane by altering the cholesterol/phospholipid ratio. Furthermore, such changes not only mediate enhanced expression of antigen on the cell surface but may drive the cells to growth arrest and apoptosis. These results were obtained by employing x-ray diffraction, electron microscopy, and DNA analysis.

Unusual genome organisation in Entamoeba histolytica leads to two overlapping transcripts

We have isolated homologs of the mini chromosome maintenance (MCM) gene family from the parasitic protozoan Entamoeba histolytica. The full length genomic and cDNA clones for the Eh MCM3 gene have been characterised. The Eh MCM3 gene is much smaller than the Saccharomyces cerevisiae MCM3 gene and other eukaryotic homologs of the MCM3/P1 family. The predicted Eh Mcm3 protein was 597 amino acids long and showed 37 and 46% positional identity with the Sc Mcm3 and the mouse P1 homologs respectively. While proceeding along the chromosome from the Eh MCM3 gene, we have identified a homolog (Eh PAK) of the murine p21 activated kinase (Rn KPAK), or S. cerevisiae STE20. Eh PAK lies 126 bp upstream of the Eh MCM3 gene. The predicted Eh p21 activated kinase protein was 459 amino-acids long and showed 33% positional identity with the murine p21 activated kinase and its yeast homolog Ste20. Analysis of cDNA and genomic sequences shows that the 3' untranslated region (UTR) of the Eh PAK mRNA and the 5' UTR of the Eh MCM3 mRNA are transcribed from a common 40 bp genomic segment. This is the first report of an amoeba gene being physically linked to a second gene such that their transcripts are overlapping and there is no non-transcribed intergenic region between the two genes. Primer extension studies have confirmed that unlike most E. histolytica genes, which have short 5' UTRs, the Eh MCM3 mRNA has a 126 bp long 5' UTR and the Eh PAK mRNA has a 265 bp long 5' UTR.

Does Entamoeba histolytica cause irritable bowel syndrome?

BACKGROUND

Symptoms of patients with irritable bowel syndrome (IBS) closely mimic those of patients with non-dysenteric amebic colitis.

AIM

To examine the clinical relevance of presence and types of Entamoeba histolytica in stools of patients with IBS.

METHODS

IBS was diagnosed by Manning's criteria. Stool examination was done 4-weekly for 48 weeks to detect E. histolytica cysts or trophozoites. Patients underwent initial sigmoidoscopy. Sera of 22 IBS patients, 23 asymptomatic cyst passers and 36 healthy volunteers whose stools were also examined were tested for presence of antiamebic antibodies. Stools were cultured for amebae; positive cultures were subjected to polyacrylamide-gel electrophoresis (PAGE) using hexokinase (HK) isoenzyme to distinguish between pathogenic (fast-moving band) E. histolytica infection and nonpathogenic (slow band) species of Entamoeba dispar.

RESULTS

E. histolytica cultured from stool samples of four IBS patients had slow-moving band of HK on PAGE. All patients spontaneously eradicated the infection during the next eight to 24 weeks; all had negative serology for antiamebic antibodies, and normal rectal mucosa on sigmoidoscopy. No change in symptom score occurred on follow up in IBS patients, although all of them cleared the infection. Three additional E. histolytica isolates from IBS patients obtained from another laboratory also showed nonpathogenic isoenzyme pattern.

CONCLUSION

Bowel symptoms in IBS patients were not related to E. histolytica infection. The term non-dysenteric amebic colitis thus appears to be inappropriate, since it may be used erroneously for patients with IBS with nonpathogenic ameba, leading to injudicious treatment with antiamebic drugs.

The mcm17 mutation of yeast shows a size-dependent segregational defect of a mini-chromosome

Mini-chromosome-maintenance (mcm) mutants were described earlier as yeast mutants which could not stably maintain mini-chromosomes. Out of these, the ARS-specific class has been more extensively studied and is found to lose chromosomes and mini-chromosomes due to a defect in the initiation of DNA replication at yeast ARSs. In the present study we have identified a number of mcm mutants which show size-dependent loss of mini-chromosomes. When the size of the mini-chromosome was increased, from about 15 kb to about 60 kb, there was a dramatic increase in its mitotic stability in these mutants, but not in the ARS-specific class of mutants. One mutant, mcm17, belonging to the size-dependent class was further characterized. In this mutant, cells carried mini-chromosomes in significantly elevated copy numbers, suggesting a defect in segregation. This defect was largely suppressed in the 60-kb mini-chromosome. A non-centromeric plasmid, the TRP1ARS1 circle, was not affected in its maintenance. This mutant also displayed enhanced chromosome-III loss during mitosis over the wild-type strain, without elevating mitotic recombination. Cloning and sequencing of MCM17 has shown it to be the same as CHL4, a gene required for chromosome stability. This gene is non-essential for growth, as its disruption or deletion from the chromosome did not affect the growth-rate of cells at 23 degrees C or 37 degrees C. This work suggests that centromere-directed segregation of a chromosome in yeast is strongly influenced by its length.

Evaluation of frictional resistance in esthetic brackets

The purpose of this study was to measure the frictional forces generated between composite, ceramic, and metal brackets and selected wire alloy-size combinations with elastomeric and stainless steel ligatures in a dry environment. Four types of composite, one ceramic, one sapphire, and one metal bracket were tested with stainless steel, nickel-titanium, and beta-titanium wires. The testing was performed with two wire sizes in the 0.018-inch slot brackets and three wire sizes in the 0.022-inch slot bracket. The recently introduced composite brackets were found to offer lower frictional resistance than the ceramic and stainless steel brackets, regardless of the wire size, wire alloy, and type of ligation. The wire alloy with the least friction was stainless steel, followed by beta-titanium and nickel-titanium. Mean variability in friction, as reflected by the magnitude of the standard deviations, was 2.7 to 3 times more with the stainless steel ligation than the elastomeric ligation.

A multicentre evaluation of the CA 15-3 assay, CA 19-9 assay and CA 125 II assay on the Bayer Immuno 1 System

The analytical performance of the tumour markers CA 15-3 assay, CA 19-9 assay and Ca 125 II assay on the Bayer Immuno I System was studied according to a revised version of the ECCLS guidelines (Haeckel R. In: Evaluation methods in laboratory medicine, Weinheim, VCH Verlag 1993:47-69) in a multicentre evaluation involving five laboratories. Determination of the 3 analytes generated more than 6000 data. On the Bayer Immuno I System, the imprecisions of the CA 15-3 assay, CA 19-9 assay and CA 125 II assay were better than those found for comparison methods. The median recovery over all five laboratories of system assigned values in control sera was within the 1-s range for the three tumour marker assays. No deviation of linearity could be detected experimentally for all assays. Results for patients' samples showed acceptable agreement between the Bayer Immuno 1 system and several different comparison methods in most cases. One exception was the CA 15-3 assay in comparison with the MCA assay from Roche Diagnostic Systems, where the large difference in values is due to the use of different antibodies and calibrators in the two assays. No carry-over effects could be detected. The selective Bayer Immuno 1 system is fully automated; its practicability was rated as high.

The effect of in vitro bacterial association on virulence of Entamoeba histolytica

When trophozoites of axenic E. histolytica strains NIH : 200 were associated in vitro with Escherichia coli K12 for three hours at 37 degrees C, the virulence was enhanced as shown by increased cytopathogenicity to baby hamster kidney (BHK) cell monolayer. Further, the trophozoites were observed to adhere to the polystyrene surface, a hitherto unreported phenomenon. The co-association of E. histolytica trophozoites with Bacteroides fragilis and Clostridium perfringens for three hours duration at 37 degrees C neither led to increase in cytotoxicity potential nor to adherence phenomenon; in contrast significant inhibition of cytotoxicity was observed. We have thus shown that while co-association of E. histolytica (NIH : 200) with E. coli K12 leads to enhanced amoebic virulence, that with anaerobic bacteric leads to its inhibition.

Reciprocal interactions between occlusion and motion computations

The "aperture problem" refers to the inherent ambiguity of the motion generated by an untextured contour moving within an aperture. The limited spatial extent of the receptive fields of neurons in cortical areas like V1 and MT render them susceptible to this problem. Most psychophysical experiments have probed how the visual system overcomes the aperture problem by presenting moving contours behind one or more simulated apertures. The assumption has been that the computational ambiguities that arise in resolving these displays are equivalent to the computational problems created by receptive fields that sample a small region of visual space. Evidence is presented here that challenges this view. We demonstrate that a fundamental computational difference in the interpretation of contour terminators arises in these two variants of the aperture problem. When the aperture is a receptive field, and a moving contour extends beyond its boundaries, the contour "terminators" delimit the boundaries of the receptive field, not the ends of the contour. In contrast, when a moving contour is viewed through a simulated aperture, the contour terminators are generated by the occluding edges of the aperture. In a series of experiments, we show that reciprocal interactions arise between computations of occlusion and those of motion direction and integration. Our results demonstrate that the visual system solves the aperture problem by decomposing moving contours into moving segments, and unpaired terminators that arise from the accretion and deletion of contours behind occluding edges, generating both coherent motion and illusory occluding surfaces.

Role of learning in three-dimensional form perception

One of the most remarkable characteristics of the human visual system is its ability to perceive specific three-dimensional forms in single two-dimensional contour images. This has often been attributed to a few general purpose and possibly innately specified shape biases, such as those favouring symmetry and other structural regularities (Fig. 1). An alternative approach proposed by the early empiricists and since tested suggests that this ability may also be acquired from visual experience, with the three-dimensional percept being the manifestation of a learned association between specific two-dimensional projections and the correlated three-dimensional structures. These studies of shape learning have been considered inconclusive, however, because their results can potentially be accounted for as cognitive decisions that might have little to do with shape perception per se. Here we present an experimental system that enables objective verification of the role of learning in shape perception by rendering the learning to be perceptually manifest. We show that the human visual system can learn associations between arbitrarily paired two-dimensional pictures and (projectionally consistent) three-dimensional structures. These results implicate high-level recognition processes in the task of shape perception.

The coherence of subjective gratings

Two differently oriented moving gratings when superimposed, are often seen to move coherently in a direction quite different from that of either grating's. By varying the characteristics of the component gratings researchers have been able to study specific aspects of the motion processing mechanisms in the primate visual system. Here we report the results of experiments performed with a class of subjective gratings. We find that observers perceive coherence and are able to accurately report pattern velocity with our stimuli. These results have implications for some key issues concerning strategies and mechanisms for motion estimation in the human visual system.

Neoplastic transformation and aberrant cell-cell interactions in genetic mosaics of lethal(2)giant larvae (lgl), a tumor suppressor gene of Drosophila

Homozygosity for lethal(2)giant larvae (lgl), a mutation in a tumor suppressor gene of Drosophila, induces neoplasia of the imaginal discs. To explore the developmental capacities of lgl mutant cells, we have investigated their growth and differentiation in genetic mosaics. Adult wings mosaic for lgl displayed abnormal growth and differentiation of the lgl mutant and neighboring wild-type cells, suggesting aberrant cell-cell interactions during development. lgl mutant clones also straddled the anteroposterior boundary of the wing imaginal disc, apparently due to failure of the cells of the anterior and the posterior compartment to segregate at the boundary. To further test if anteroposterior compartmentalization takes place in the neoplastic imaginal discs of lgl mutant larvae, we studied the expression of an engrailed (en)-specific lacZ reporter gene during progressive stages of their tumorous growth. Our results show that en is activated in the posterior compartments of the neoplastic imaginal discs. However, during later stages of tumorous overgrowth, the en-expressing and nonexpressing cells appear to show extensive intermixing. These observations suggest that neoplastic transformation of imaginal discs involves loss of their normal cell-cell interactions and signaling.

Epithelial hyperplasia of imaginal discs induced by mutations in Drosophila tumor suppressor genes: growth and pattern formation in genetic mosaics

Lethal mutations in the giant discs (lgd) and fat (ft) tumor suppressor genes of Drosophila cause epithelial hyperplasia in all imaginal discs. By contrast, mutations in the vestigial (vg) gene adversely affect cell viability in the wing imaginal discs and consequently cause loss of pattern in the adult wings. However, combining homozygous lgd or ft mutations with homozygous vg1 increases the size of the wing imaginal discs and partially restores the bristle pattern in the wings of pharate adults. Comparable pattern restoration in vg1 wings is also induced by a newly isolated weak hypomorphic lgd3 allele. Further, mosaic analysis revealed that whereas lgd clones generated by the Minute technique display abnormal differentiation, those induced in a homozygous vg1 background exhibit autonomous restoration of wing pattern. These results suggest that pattern restoration in vg1 wings can serve as an assay for hyperplasia induced by mutations in Drosophila tumor suppressor genes.

An improved method for chemical devitellinization of X-gal stained Drosophila embryos

In Drosophila developmental biological studies, X-gal staining is commonly employed to study the spatio-temporal expression of the lacZ reporter gene in the transformed flies or their embryos. Study of the lacZ pattern in embryos often suffers from the lack of an efficient and high yielding technique for devitellinization of X-gal stained embryos. Devitellinization techniques employed during antibody staining, in situ hybridization or embryonic cuticular preparations generally do not give satisfactory results when used for similar purpose in X-gal stained embryos. This results in the flaky appearance of the blue stain. We present here an improved chemical devitellinization technique which gives a high yield of devitellinized embryos and a better resolution of the X-gal staining pattern.

The mcm2-1 mutation of yeast causes DNA damage with a RAD9 requirement for repair

The minichromosome maintenance mutation, mcm2-1, has been found to synthesize damaged DNA at 35 degrees C. Growth at this temperature rendered the mutant strain more sensitive to killing by ultraviolet irradiation. DNA damage could also be detected by pulsed-field gel electrophoresis, where a higher fraction of the DNA loaded was retained in the inserts at the wells. During the exponential phase of growth at this temperature about 50% of the cells had large buds, with the nucleus at or near the neck of the bud in most cases. The incorporation of the rad9 deletion in the mcm2-1-carrying strain caused a reduction in the percentage of large-budded cells and a moderate loss of cell viability. The results are consistent with mcm2-1 causing DNA damage leading to the arrest of cells in the S/G2 phase of the cell cycle, which was partially dependent on the RAD9 gene product.

A 61-kb ring chromosome shows an ARS-dependent increase in its mitotic stability in the mcm2 mutant of yeast

We have studied the effects of ARS addition and deletion on the maintenance of a 61-kb ring derivative of chromosome III in a minichromosome maintenance mutant of yeast carrying the mcm2-1 mutation. When this ring chromosome, CIIIR, had either of its two strong origins deleted, the resultant chromosome showed a much greater instability in the mutant as compared to that of the wild-type strain. Integration of more ARSs improved the maintenance of CIIIR in the mutant but not in the wild-type strain. Increase in the size of CIIIR, without any ARS addition, did not improve the stability in either strain. A spontaneous revertant for improved growth at 35 degrees C also co-reverted for minichromosome and CIIIR maintenance. The results suggest that ARS malfunctioning leads to minichromosome and chromosome loss from mutant cells, affecting their growth at higher temperatures.

A 5-year study of caesarean hysterectomy cases

There were 53 cases where caesarean hysterectomy was done during the last 5 years at Eden Hospital, Calcutta. Majority of the cases were in the age group of 22-32 years and parity varied from 0 to 6. There were 54.71% cases which were due to rupture of previous caesarean section scar mostly lower uterine segment done in teaching institutions. Seventy per cent cases were booked. Only 8 babies survived following caesarean hysterectomy. Maternal mortality was nil. By good intranatal monitoring, more vigilance, performing less caesarean section and better health education one can lower the incidence of caesarean hysterectomy.

Studies on the aetiology of coeliac disease: no evidence for lectin-like components in wheat gluten

In an approach to examine the lectin-hypothesis in the pathogenesis of coeliac disease, the presence of lectin-like components in three wheat gluten preparations known to induce coeliac disease, gliadin, Frazer fraction III and an acetic acid/ethanol extract of gluten, was investigated. Lectin-like components in these wheat gluten preparations were traced in binding studies employing a variety of model glycoproteins glycosylated with the different types of N-linked oligosaccharides, i.e., those of the high mannose-, complex- and hybrid-type. Binding affinity of wheat proteins to these glycoproteins was analyzed by affinity dotting and blotting techniques and was compared to that of the well characterized lectins Galanthus nivalis agglutinin, Concanavalin A and wheat germ agglutinin. Though the three wheat gluten preparations exhibited binding reactivity for distinct model glycoproteins, no correlation was found between the type of N-glycosylation of the model glycoproteins and their binding capability to the different wheat gluten preparations. Moreover, binding of the three gluten preparations to the model glycoproteins could not be inhibited by competitive saccharides (methyl-alpha-D-mannopyranoside, N-acetyl-D-glucosamine, mannan). Enzymatic deglycosylation of the ligand glycoproteins with endo-beta-N-acetylglucosaminidase H (Endo H, EC 3.2.1.96) or peptide N-glycosidase F (PNGase F, EC 3.5.1.52) abolished their binding reactivity for the plant lectins, but did not affect binding of the wheat gluten preparations. These results give no evidence for the presence of lectin-like components in wheat gluten preparations and do question the 'lectin hypothesis' of coeliac disease.

Analysis of haemoglobin variants using immobilized pH gradients

We present a new method for analysis of haemoglobin variants in immobilized pH gradients. The isoelectric fractionation is performed in polyacrylamide gels with copolymerized pH gradients between pH 7.0 and 8.0. The common haemoglobin variants (HbA, HbF, HbS, HbC, HbE and HbA2) are clearly resolved within this pH range. The high resolving power and reproducibility of immobilized pH gradients combined with extremely short separation times make this fractionation technique superior to all electrokinetic procedures used for haemoglobin analysis. At present, isoelectric focusing in immobilized pH gradients is a complementary tool for haemoglobin analysis when classical electrophoretic techniques do not provide sufficient resolution. We hope that in the future this technique will gain the popularity it deserves.

An investigation into pellet dispersion ballistics

Existing works on pellet dispersion ballistics are confined to some data-based models derived from statistical analysis of observed patterns on targets but the underlying process causing the dispersion lacks due attention. The present article delves into the relatively unexplored areas of dispersion phenomena, and attempts to develop a theoretical model for general application. The radial velocity distribution of pellets has been worked out by probing into the physical process of dispersion based on transfer of momentum from undispersed shot mass to dispersed pellets. The ratio 2u/v0 (u = root mean square (r.m.s.) radial velocity and v0 = muzzle velocity of the pellets) is found to be fairly constant for a fixed gun-ammunition combination and has been suitably designated as 'Dispersion Index' (DI) characterising its dispersion capability. The present model adequately accounts for pellet distribution on targets and it appears that 'Effective Shot Dispersion' (ESD) as introduced by Mattoo and Nabar [ESD = [(4/N0)sigma Ri2]1/2, where N(0) is the total number of pellets and Ri is the radial distance of the i-th pellet from centre of pattern], gives a faithful numerical measure of overall dispersion at a given distance. A relationship between ESD and firing distance, incorporating the effects of air resistance and gravity has been worked out, which reveals that DI controls the dispersion at a given distance. For small distances (less than 20 m) the relation reduces to a linear one, as already observed empirically and looks like ESD = E0+DI x firing distance, E0 being a parameter dependent on gun and ammunition. The present model, unlike earlier ones, is versatile enough to explain the natures of the dependence of dispersion on firing distance as well as on gun-ammunition parameters, which are essential for a faithful reconstruction of a crime scene. The model has been tested with such experimental data as are available and reasonable agreement is observed.

The mcm2 mutation of yeast affects replication, rather than segregation or amplification of the two micron plasmid

We have studied the maintenance of the endogenous two micron (2 mu) plasmid in a strain of yeast carrying the nuclear mutation mcm2. This mutation, earlier shown to affect the maintenance of yeast minichromosomes in an ARS-dependent manner, also affected the copy number of the 2 mu plasmid. The effect was more pronounced at 35 degrees C leading to the elimination of the plasmid from the cells cultured at this temperature. The mutant cells could be efficiently cured of the circle by transformation with 2 mu ORI-carrying hybrid vectors, an observation consistent with the low copy number of the endogenous plasmid. A chromosomal revertant of this mutant for another ARS(ARS1) was found also to confer stability on the 2 mu ORI-carrying minichromosomes and had elevated levels of the endogenous plasmid. The mutation neither affected the segregation nor the amplification process mediated by site-specific recombination at FRT sites requiring the FLP gene-encoded protein action. ARS131C, an ARS that was unaffected in the mutant at 25 degrees C, could elevate the copy number of a 2 mu hybrid vector in the mutant cells. In view of these results, some aspects of segregation and copy number control of the endogeneous plasmid have been discussed. We propose that the mutation impairs the 2 mu ORI function, leading to its loss.

Immobilized pH 2.5-11 gradients for two-dimensional electrophoresis

Extremely wide immobilized pH gradients, pH 2.5-11, for isoelectric separation of complex protein mixtures are described. These pH gradients are theoretically and practically the maximum that can be achieved at present with the available acrylamido buffers and titrants. Conditions are described for reducing conductivity and electroendosmosis in extreme pH ranges. Furthermore, new conditions are described for the separation of proteins in the second dimension. Using this protocol, nearly all the possible cellular products can be separated in one single two-dimensional map.

Rapid and simple method for the identification of apolipoprotein E isomorphic phenotypes from whole serum

For the identification of apolipoprotein E isomorphic phenotypes, fresh or thawed serum was analyzed without prior delipidation or other pretreatment. Using 5% polyacrylamide gels with a 40 mm interelectrode distance, the isoforms were separated by isoelectric focusing in immobilized pH gradients ranging from pH 5 to 6.5, and transferred onto polyvinylidene difluoride membranes by contact blotting for 1 h. The apolipoprotein E isoforms were identified following immunostaining. The electrophoresis required less than 2 h and the entire procedure could be completed within 6 h.