Genetic diversity of Plasmodium vivax isolates from pregnant women in the Western Brazilian Amazon: a prospective cohort study

Background

Each year, 92 million pregnant women are at risk of contracting malaria during pregnancy, with the underestimation of the mortality and morbidity burden associated with Plasmodium vivax. During pregnancy, P. vivax infection is associated with low birth weight, maternal anaemia, premature delivery, and stillbirth. In the State of Acre (Brazil), high transmission leaves pregnant women at greater risk of contracting malaria and having a greater number of recurrences. The study of genetic diversity and the association of haplotypes with adverse pregnancy effects is of great importance for the control of the disease. Here we investigate the genetic diversity of P. vivax parasites infecting pregnant women across their pregnancies.

Methods

P. vivax DNA was extracted from 330 samples from 177 women followed during pregnancy, collected in the State of Acre, Brazil. All samples were negative for Plasmodium falciparum DNA. Sequence data for the Pvmsp1 gene was analysed alongside data from six microsatellite (MS) markers. Allelic frequencies, haplotype frequencies, expected heterozygosity (HE) were calculated. Whole genome sequencing (WGS) was conducted on four samples from pregnant women and phylogenetic analysis performed with other samples from South American regions.

Findings

Initially, the pregnant women were stratified into two groups-1 recurrence and 2 or more recurrences-in which no differences were observed in clinical gestational outcomes or in placental histological changes between the two groups. Then we evaluated the parasites genetically. An average of 18.5 distinct alleles were found at each of the MS loci, and the HE calculated for each marker indicates a high genetic diversity occurring within the population. There was a high percentage of polyclonal infections (61.7%, 108/175), and one haplotype (H1) occurred frequently (20%), with only 9 of the haplotypes appearing in more than one patient.

Interpretation

Most pregnant women had polyclonal infections that could be the result of relapses and/or re-infections. The high percentage of H1 parasites, along with the low frequency of many other haplotypes are suggestive of a clonal expansion. Phylogenetic analysis shows that P. vivax population within pregnant women clustered with other Brazilian samples in the region.

Funding

FAPESP and CNPq - Brazil.

De Novo Assembly of Plasmodium knowlesi Genomes From Clinical Samples Explains the Counterintuitive Intrachromosomal Organization of Variant SICAvar and kir Multiple Gene Family Members

Plasmodium knowlesi, a malaria parasite of Old World macaque monkeys, is used extensively to model Plasmodium biology. Recently, P. knowlesi was found in the human population of Southeast Asia, particularly Malaysia. P. knowlesi causes uncomplicated to severe and fatal malaria in the human host with features in common with the more prevalent and virulent malaria caused by Plasmodium falciparum. As such, P. knowlesi presents a unique opportunity to develop experimental translational model systems for malaria pathophysiology informed by clinical data from same-species human infections. Experimental lines of P. knowlesi represent well-characterized genetically stable parasites, and to maximize their utility as a backdrop for understanding malaria pathophysiology, genetically diverse contemporary clinical isolates, essentially wild-type, require comparable characterization. The Oxford Nanopore PCR-free long-read sequencing platform was used to sequence and de novo assemble P. knowlesi genomes from frozen clinical samples. The sequencing platform and assembly pipelines were designed to facilitate capturing data and describing, for the first time, P. knowlesi schizont-infected cell agglutination (SICA) var and Knowlesi-Interspersed Repeats (kir) multiple gene families in parasites acquired from nature. The SICAvar gene family members code for antigenically variant proteins analogous to the virulence-associated P. falciparum erythrocyte membrane protein (PfEMP1) multiple var gene family. Evidence presented here suggests that the SICAvar family members have arisen through a process of gene duplication, selection pressure, and variation. Highly evolving genes including PfEMP1family members tend to be restricted to relatively unstable sub-telomeric regions that drive change with core genes protected in genetically stable intrachromosomal locations. The comparable SICAvar and kir gene family members are counter-intuitively located across chromosomes. Here, we demonstrate that, in contrast to conserved core genes, SICAvar and kir genes occupy otherwise gene-sparse chromosomal locations that accommodate rapid evolution and change. The novel methods presented here offer the malaria research community not only new tools to generate comprehensive genome sequence data from small clinical samples but also new insight into the complexity of clinically important real-world parasites.

Adverse pregnancy outcomes are associated with Plasmodium vivax malaria in a prospective cohort of women from the Brazilian Amazon

Background

Malaria in Brazil represents one of the highest percentages of Latin America cases, where approximately 84% of infections are attributed to Plasmodium (P.) vivax. Despite the high incidence, many aspects of gestational malaria resulting from P. vivax infections remain poorly studied. As such, we aimed to evaluate the consequences of P. vivax infections during gestation on the health of mothers and their neonates in an endemic area of the Amazon.

Methods and findings

We have conducted an observational cohort study in Brazilian Amazon between January 2013 and April 2015. 600 pregnant women were enrolled and followed until delivery. After applying exclusion criteria, 329 mother-child pairs were included in the analysis. Clinical data regarding maternal infection, newborn’s anthropometric measures, placental histopathological characteristics, and angiogenic and inflammatory factors were evaluated. The presence of plasma IgG against the P. vivax (Pv) MSP1₁₉ protein was used as marker of exposure and possible associations with pregnancy outcomes were analyzed. Multivariate logistic regression analysis revealed that P. vivax infections during the first trimester of pregnancy are associated with adverse gestational outcomes such as premature birth (adjusted odds ratio [aOR] 8.12, 95% confidence interval [95%CI] 2.69–24.54, p < 0.0001) and reduced head circumference (aOR 3.58, 95%CI 1.29–9.97, p = 0.01). Histopathology analysis showed marked differences between placentas from P. vivax-infected and non-infected pregnant women, especially regarding placental monocytes infiltrate. Placental levels of vasomodulatory factors such as angiopoietin-2 (ANG-2) and complement proteins such as C5a were also altered at delivery. Plasma levels of anti-PvMSP1₁₉ IgG in infected pregnant women were shown to be a reliable exposure marker; yet, with no association with improved pregnancy outcomes.

Conclusions

This study indicates that P. vivax malaria during the first trimester of pregnancy represents a higher likelihood of subsequent poor pregnancy outcomes associated with marked placental histologic modification and angiogenic/inflammatory imbalance. Additionally, our findings support the idea that antibodies against PvMSP1₁₉ are not protective against poor pregnancy outcomes induced by P. vivax infections.

Malaria during pregnancy is associated with adverse effects on the fetus and the newborn. As far as we know, no study has previously investigated in a single work, the link between Plasmodium vivax malaria in pregnancy and poor gestational outcomes, alteration of the newborn’s anthropometric profile, placental lesions, angiogenic and inflammatory factors, and humoral immunity against the parasite. For this purpose, we investigated the association between P. vivax malaria during pregnancy and newborn’s anthropometric profile, placental pathology, gestational outcomes, and the presence of IgG against P. vivax MSP1₁₉ that may confer protection against infection during pregnancy. We performed a large cohort study of malaria during pregnancy that analyzed data from mother-child pairs delivered between 2013 and 2015 in the Southwestern Brazilian Amazonian region. By evaluating data from 329 pregnancies, we found that P. vivax malaria during the first pregnancy trimester is significantly associated with the occurrence of preterm birth, low birth weight, and reduced newborn head circumference and body length. We also noted that P. vivax malaria in pregnancy promoted placental lesions and homeostasis imbalance, characterized by increased syncytial nuclear aggregates, fibrin deposition, and monocytes/leukocytes infiltrate, as well as imbalanced angiogenic factors, leptin, and cytokines. We observed that pregnant women with IgG against P. vivax MSP1₁₉ are not protected against poor pregnancy outcomes caused by P. vivax infections during pregnancy. Our observations improve our understanding of the disease and P. vivax burden during pregnancy, changing the current paradigm of the outcome of P. vivax malaria in pregnancy. That may represent a long-term severe consequence for the affected populations living in P. vivax-endemic regions. Our results also indicate that IgG against P. vivax MSP1₁₉ is not associated with protection from poor pregnancy outcomes, excluding this protein as a possible vaccination target that can prevent adverse outcomes caused by P. vivax infections during pregnancy.

Association of Malaria Infection During Pregnancy With Head Circumference of Newborns in the Brazilian Amazon

Importance

Malaria during pregnancy is associated with adverse events for the fetus and newborn, but the association of malaria during pregnancy with the head circumference of the newborn is unclear.

Objective

To investigate the association of malaria during pregnancy with fetal head growth.

Design, Setting, and Participants

Two cohort studies were conducted at the general maternity hospital of Cruzeiro do Sul (Acre, Brazil) in the Amazonian region. One cohort study prospectively enrolled noninfected and malaria-infected pregnant women who were followed up until delivery, between January 2013 and April 2015. The other cohort study was assembled retrospectively using clinical and malaria data from all deliveries that occurred between January 2012 and December 2013. Data analyses were conducted from January to August 2017 and revised in November 2018. Clinical data from pregnant women and anthropometric measures of their newborns were evaluated. A total of 600 pregnant women were enrolled through volunteer sampling (prospective cohort study), and 4697 pregnant women were selected by population-based sampling (retrospective cohort study). After application of exclusion criteria, data from 251 (prospective cohort study) and 232 (retrospective cohort study) malaria-infected and 158 (prospective cohort study) and 3650 (retrospective cohort study) noninfected women were evaluated.

Exposure

Malaria during pregnancy.

Main Outcomes and Measures

The primary end point was the incidence of altered head circumference in newborns delivered from malaria-infected mothers compared with that from noninfected mothers. Secondary end points included measures of placental pathology relative to newborn head circumference.

Results

In total, 4291 maternal-child pairs were analyzed. Among 409 newborns in the prospective cohort study, the mothers of 251 newborns had malaria during pregnancy, infected with Plasmodium vivax, Plasmodium falciparum, or both. Among 3882 newborns in the retrospective cohort study, 232 were born from mothers that had malaria during pregnancy. The prevalence of newborns with a small head (19 [30.7%] in the prospective cohort study and 30 [36.6%] in the retrospective cohort study) and the prevalence of microcephaly among newborns (5 [8.1%] in the prospective cohort study and 6 [7.3%] in the retrospective cohort study) were higher among newborns from women infected with P falciparum during pregnancy. Multivariate logistic regression analyses revealed that P falciparum infection during pregnancy represented a significant risk factor for the occurrence of small head circumference in newborns (prospective cohort study: odds ratio, 3.15; 95% CI, 1.52-6.53; P = .002; retrospective cohort study: odds ratio, 1.91; 95% CI, 1.21-3.04; P = .006). Placental pathologic findings corroborated this association, with more syncytial nuclear aggregates and inflammatory infiltrates occurring in placentas of newborns born with decreased head circumference.

Conclusions and Relevance

This study indicates that falciparum malaria during pregnancy is associated with decreased head circumference in newborns, which is in turn associated with evidence of placental malaria.

Large-scale whole genome sequencing of M. tuberculosis provides insights into transmission in a high prevalence area

To improve understanding of the factors influencing tuberculosis transmission and the role of pathogen variation, we sequenced all available specimens from patients diagnosed over 15 years in a whole district in Malawi. Mycobacterium tuberculosis lineages were assigned and transmission networks constructed, allowing ≤10 single nucleotide polymorphisms (SNPs) difference. We defined disease as due to recent infection if the network-determined source was within 5 years, and assessed transmissibility from forward transmissions resulting in disease. High-quality sequences were available for 1687 disease episodes (72% of all culture-positive episodes): 66% of patients linked to at least one other patient. The between-patient mutation rate was 0.26 SNPs/year (95% CI 0.21–0.31). We showed striking differences by lineage in the proportion of disease due to recent transmission and in transmissibility (highest for lineage-2 and lowest for lineage-1) that were not confounded by immigration, HIV status or drug resistance. Transmissions resulting in disease decreased markedly over time.

DOI:http://dx.doi.org/10.7554/eLife.05166.001

Tuberculosis is an important public health threat around the globe and is particularly common in developing countries. It is difficult to control the spread of the disease because the bacteria that cause it can spread when an infected individual coughs or sneezes. It may take years for an infected individual to develop symptoms of tuberculosis so it can be hard to trace the source of an outbreak, and people infected with HIV are particularly susceptible to the disease.

The bacterium that causes the majority of cases of tuberculosis is called Mycobacterium tuberculosis. There are several different varieties or ‘lineages’ of M. tuberculosis, and it is thought that they may vary in their ability to spread and cause disease. However, the results of previous studies have been inconsistent and there also seems to be a lot of variation between strains within the same lineage.

In this study, Guerra-Assunção et al. used an approach called whole genome sequencing alongside more traditional methods to study the spread of tuberculosis in Malawi. They sequenced the genomes of every available sample of M. tuberculosis collected from patients in the Karonga district of Malawi over a 15-year period. This produced high-quality DNA sequence data about the bacteria responsible for almost 1700 cases of disease.

Using this massive amount of data, Guerra-Assunção et al. constructed networks that showed how the bacteria had spread in the community. This revealed that there were differences between the ability of the various M. tuberculosis lineages to cause disease and to spread in communities. For example, lineage 1 was less likely than the other lineages to cause disease soon after infecting an individual and was less able to spread.

The data also show that the proportion of cases of disease due to recent infection declined substantially during the 15-year period. This indicates that the tuberculosis and HIV control programmes in the area have been successful.

Guerra-Assunção et al.'s findings show that it is possible to understand how tuberculosis is transmitted on a large scale. The next challenge is to understand why the lineages differ in their ability to cause disease and spread between individuals.

DOI:http://dx.doi.org/10.7554/eLife.05166.002

Fc gamma receptor IIa-H131R polymorphism and malaria susceptibility in sympatric ethnic groups, Fulani and Dogon of Mali

It has been previously shown that there are some interethnic differences in susceptibility to malaria between two sympatric ethnic groups of Mali, the Fulani and the Dogon. The lower susceptibility to Plasmodium falciparum malaria seen in the Fulani has not been fully explained by genetic polymorphisms previously known to be associated with malaria resistance, including haemoglobin S (HbS), haemoglobin C (HbC), alpha-thalassaemia and glucose-6-phosphate dehydrogenase (G6PD) deficiency. Given the observed differences in the distribution of FcγRIIa allotypes among different ethnic groups and with malaria susceptibility that have been reported, we analysed the rs1801274-R131H polymorphism in the FcγRIIa gene in a study of Dogon and Fulani in Mali (n = 939). We confirm that the Fulani have less parasite densities, less parasite prevalence, more spleen enlargement and higher levels of total IgG antibodies (anti-CSP, anti-AMA1, anti-MSP1 and anti-MSP2) and more total IgE (P < 0.05) compared with the Dogon ethnic group. Furthermore, the Fulani exhibit higher frequencies of the blood group O (56.5%) compared with the Dogon (43.5%) (P < 0.001). With regard to the FcγRIIa polymorphism and allele frequency, the Fulani group have a higher frequency of the H allele (Fulani 0.474, Dogon 0.341, P < 0.0001), which was associated with greater total IgE production (P = 0.004). Our findings show that the FcγRIIa polymorphism might have an implication in the relative protection seen in the Fulani tribe, with confirmatory studies required in other malaria endemic settings.

The genome of the simian and human malaria parasite Plasmodium knowlesi

Plasmodium knowlesi is an intracellular malaria parasite whose natural vertebrate host is Macaca fascicularis (the 'kra' monkey); however, it is now increasingly recognized as a significant cause of human malaria, particularly in southeast Asia. Plasmodium knowlesi was the first malaria parasite species in which antigenic variation was demonstrated, and it has a close phylogenetic relationship to Plasmodium vivax, the second most important species of human malaria parasite (reviewed in ref. 4). Despite their relatedness, there are important phenotypic differences between them, such as host blood cell preference, absence of a dormant liver stage or 'hypnozoite' in P. knowlesi, and length of the asexual cycle (reviewed in ref. 4). Here we present an analysis of the P. knowlesi (H strain, Pk1(A+) clone) nuclear genome sequence. This is the first monkey malaria parasite genome to be described, and it provides an opportunity for comparison with the recently completed P. vivax genome and other sequenced Plasmodium genomes. In contrast to other Plasmodium genomes, putative variant antigen families are dispersed throughout the genome and are associated with intrachromosomal telomere repeats. One of these families, the KIRs, contains sequences that collectively match over one-half of the host CD99 extracellular domain, which may represent an unusual form of molecular mimicry.

Perturbation analysis: a simple method for filtering SNPs with erroneous genotyping in genome-wide association studies

We introduce a simple and yet scientifically objective criterion for identifying SNPs with genotyping errors due to poor clustering. This yields a metric for assessing the stability of the assigned genotypes by evaluating the extent of discordance between the calls made with the unperturbed and perturbed intensities. The efficacy of the metric is evaluated by: (1) estimating the extent of over-dispersion of the Hardy-Weinberg equilibrium chi-square test statistics; (2) an interim case-control study, where we investigated the efficacy of the introduced metric and standard quality control filters in reducing the number of SNPs with evidence of phenotypic association which are attributed to genotyping errors; (3) investigating the call and concordance rates of SNPs identified by perturbation analysis which have been genotyped on both Affymetrix and Illumina platforms. Removing SNPs identified by the extent of discordance can reduce the degree of over-dispersion of the HWE test statistic. Sensible use of perturbation analysis in an association study can correctly identify SNPs with problematic genotyping, reducing the number required for visual inspection. SNPs identified by perturbation analysis had lower call and concordance rates, and removal of these SNPs significantly improved the performance for the remaining SNPs.

Interferon regulatory factor-1 polymorphisms are associated with the control of Plasmodium falciparum infection

We describe the haplotypic structure of the interferon regulatory factor-1 (IRF-1) locus in two West African ethnic groups, Fulani and Mossi, that differ in their susceptibility and immune response to Plasmodium falciparum malaria. Both populations showed significant associations between IRF-1 polymorphisms and carriage of P. falciparum infection, with different patterns of association that may reflect their different haplotypic architecture. Genetic variation at this locus does not therefore account for the Fulani-specific resistance to malaria while it could contribute to parasite clearance's ability in populations living in endemic areas. We then conducted a case-control study of three haplotype-tagging single nucleotide polymorphisms (htSNPs) in 370 hospitalised malaria patients (160 severe and 210 uncomplicated) and 410 healthy population controls, all from the Mossi ethnic group. All three htSNPs showed correlation with blood infection levels in malaria patients, and the rs10065633 polymorphism was associated with severe disease (P=0.02). These findings provide the first evidence of the involvement in malaria susceptibility of a specific locus within the 5q31 region, previously shown to be linked with P. falciparum infection levels.

Association of the NRG1 gene and schizophrenia: a meta-analysis

We investigated the association of the NRG1 gene and schizophrenia using meta-analytic techniques, combining all published data while restricting our analysis to studies investigating the most commonly reported single marker (SNP8NRG221533). We also investigated whether ancestry (European vs East Asian) and study design (family-based vs case-control) moderated any association. We found no evidence for an association of SNP8NRG221533 with schizophrenia, and significant between-study heterogeneity, which persisted when family-based studies were combined separately. However, when haplotype-based P-values were combined, there was evidence in support of an association of NRG1 with schizophrenia, and no evidence of between-study heterogeneity. Our meta-analysis provides support for the association of NRG1 with schizophrenia, but indicates that firmly establishing the role of NRG1 gene in schizophrenia by genetic association requires much larger sample sizes than have hitherto been reported. Association analyses and replications should take place at the level of the gene, rather than at the level of SNP, haplotype, or functional variant. Meta-analysis would then be carried out on the basis of the combination of P-values.

Apolipoproteins as Predictors of Ischaemic Stroke in Patients with a Previous Transient Ischaemic Attack

BACKGROUND

Weak associations between total and LDL cholesterol and ischaemic stroke compared with coronary heart disease (CHD) are at odds with the similar effectiveness of statin drugs in preventing ischaemic stroke and CHD, suggesting that other lipid sub-fractions that are affected by statins might be better predictors of ischaemic stroke. Apolipoprotein B levels are reduced by statins and are a stronger predictor of CHD than total and LDL cholesterol in patients both on and off statins. However, there are very few published data on apolipoproteins and stroke risk and no studies in patients with previous transient ischaemic attack (TIA).

METHODS

We performed a prospective cohort study of the associations of baseline total cholesterol, LDL, HDL, apolipoproteins A1 and B (apo A1; apo B) and risk of ischaemic stroke in 261 patients with previous TIA. Cox proportional hazards models were used to determine crude and multivariate-adjusted hazard ratios (HR) above versus below median values at 10-years follow-up.

RESULTS

The apo B/apo A1 ratio was the strongest independent predictor of ischaemic stroke (HR=2.94, 95% CI 1.43-5.88, p=0.003) followed by apo B (HR=2.26, 95% CI 1.16-4.38, p=0.02). The associations between total cholesterol, LDL, HDL, LDL/HDL ratio and apo A1 and ischaemic stroke risk did not reach statistical significance.

CONCLUSIONS

Apo B and the apo B/apo A1 ratio are predictive of ischaemic stroke in patients with previous TIA. Further studies are required to determine whether the prognostic value of apolipoprotein levels is maintained in patients on statins.

Lack of association of the COMT (Val158/108 Met) gene and schizophrenia: a meta-analysis of case-control studies

There is strong evidence for a genetic contribution to schizophrenia, but the contribution of individual candidate genes remains uncertain. We attempted to replicate a recent meta-analysis that reported an association of the catechol O-methyltransferase (COMT) Val allele with schizophrenia, and suggested that this effect may be moderated by ancestry. We included reports published subsequent to the original meta-analysis, and included a formal test of the moderating effect of ancestry in order to test whether the association operates differently in populations of European ancestry compared to populations of Asian ancestry. A corrected P-value for the 5% significance threshold was employed where appropriate, using Bonferroni's method, and studies that demonstrated departure from Hardy-Weinberg equilibrium among controls were excluded. When all studies were included in a meta-regression, there was evidence for a significant association of COMT Val allele frequency with schizophrenia case status and a significant main effect of ancestry. The interaction of COMT Val allele frequency and ancestry was also significant. However, when only studies that reported allele frequencies that did not depart significantly from Hardy-Weinberg equilibrium among controls were included, these effects were no longer significant. The results of our meta-analysis do not support an association between the COMT Val allele and schizophrenia case status, and do not support recent claims that this association may be moderated by ancestry.

Recombinant subunit vaccines: potentials and constraints

Recombinant DNA techniques have enormous potential for the development of inexpensive, safe and efficacious vaccines for the aquaculture industry. Aside from rationally attenuated pathogens, two broad categories of recombinant vaccines have been described. The first are so-called "vectored" vaccines, which consist of either viral or plasmid expression vectors harbouring genes for protective antigens from a given pathogen. The second are recombinant subunit antigens produced using heterologous protein expression systems. Less onerous from a regulatory standpoint, recombinant subunit vaccines generate strong antibody responses in recipient animals when administered parenterally with adjuvant-containing formulations. This approach is nevertheless constrained by the fact that low-cost systems for protein expression (especially E. coli, but also yeast) often generate misfolded or incorrectly processed membrane antigens that fail to protect, while more complex insect and mammalian tissue culture cells are prohibitively expensive from a production standpoint. Furthermore, subunit antigens generate less than optimal mucosal and cytotoxic T-cell responses, the last two of which are especially important for the clearance of intracellular pathogens. Fortunately, these constraints are now being overcome through the use of new generation adjuvants and delivery systems that enhance immunogenicity, as well as new expression systems for the production of viral and protozoan membrane antigens.

Creating biological membranes on the micron scale: forming patterned lipid bilayers using a polymer lift-off technique

We present a new method for creating patches of fluid lipid bilayers with conjugated biotin and other compounds down to 1 microm resolution using a photolithographically patterned polymer lift-off technique. The patterns are realized as the polymer is mechanically peeled away in one contiguous piece in solution. The functionality of these surfaces is verified with binding of antibodies and avidin on these uniform micron-scale platforms. The biomaterial patches, measuring 1 micro m-76 microm on edge, provide a synthetic biological substrate for biochemical analysis that is approximately 100x smaller in width than commercial printing technologies. 100 nm unilamellar lipid vesicles spread to form a supported fluid lipid bilayer on oxidized silicon surface as confirmed by fluorescence photobleaching recovery. Fluorescence photobleaching recovery measurements of DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiIC(18)(3))) stained bilayer patches yielded an average diffusion coefficient of 7.54 +/- 1.25 microm(2) s(-1), equal to or slightly faster than typically found in DiI stained cells. This diffusion rate is approximately 3x faster than previous values for bilayers on glass. This method provides a new means to form functionalized fluid lipid bilayers as micron-scale platforms to immobilize biomaterials, capture antibodies and biotinylated reagents from solution, and form antigenic stimuli for cell stimulation.

Cadmium effects on Ichthyophthirius: evidence for metal-sequestration in fish tissues following administration of recombinant vaccines

We are developing Tetrahymena thermophila as a delivery system for recombinant vaccines against parasitic protozoa, including the common fish parasite, Ichthyophthirius multifiliis. T. thermophila cell lines expressing I. multifiliis genes under the control of a cadmium-inducible metallothionein gene promoter conferred strong protection against a lethal parasite challenge when administered parenterally to naive fish. Nevertheless, given that heavy metals can be toxic to parasites, a question arose as to whether protection resulted from Cd residues carried over with the vaccine, rather than acquired immunity per se. To address this issue, we examined the sensitivity of I. multifiliis to Cd in vitro and determined Cd concentrations in different host tissues following i.p. injection of juvenile channel catfish with the recombinant vaccine. We found that CdCl2 at concentrations > or = 50 ppb were lethal to I. multifiliis theronts in vitro. Furthermore, Cd concentrations were clearly elevated in fish tissues and reached levels equivalent to 74 ng/g wet weight (74 ppb) in the skin within 14 days of injection with recombinant T. thermophila. Nevertheless, fish injected with non-transformed Tetrahymena grown in the presence or absence of CdCl2 showed no significant difference in either relative survival or parasite load following direct challenge with I. multifiliis.

Long term risks of stroke, myocardial infarction, and vascular death in "low risk" patients with a non-recent transient ischaemic attack

BACKGROUND

Previous studies of prognosis after a transient ischaemic attack (TIA) have recruited patients soon after the event, when the risk of stroke is very high. However, the majority of patients survive for many years after a TIA, and the need for continued preventive treatment to lower vascular risk will need to be reassessed at a later date.

OBJECTIVE

To determine the long term risks of stroke and other vascular events in patients with TIA who survive the initial high risk period.

METHODS

290 patients were studied who had initially been followed up after a TIA in the Oxford community stroke project and in a contemporaneous hospital based cohort study, and who were alive and stroke-free at the end of planned follow up in 1988. All patients were followed for a further 10 years, and the risks of major vascular events (stroke, myocardial infarction, vascular death) were determined. Standardised mortality ratios (SMR) were calculated from the observed numbers of fatal events and the number expected on the basis of age and sex in the general population.

RESULTS

Median time since last TIA was 3.8 years (interquartile range, 2.2 to 5.8 years). The risk of major vascular events was constant through time. The 10 year risk of first stroke was 18.8% (95% confidence interval (CI), 13.6 to 23.7; 45 events). The 10 year risk of myocardial infarction or death from coronary heart disease was 27.8% (95% CI, 21.8 to 33.3; 67 events) and there was a significant excess of fatal coronary events compared with that expected in the general population (SMR = 1.47; 95% CI, 1.10 to 1.93; p = 0.009). A total of 114 patients had at least one major vascular event, with a 10 year risk of any first stroke, myocardial infarction, or vascular death of 42.8% (95% CI, 36.4 to 48.5).

CONCLUSIONS

The overall risk of major vascular events remains high for 10 to 15 years after a TIA. It is important therefore that preventive treatments are continued in the long term, even in apparently "low risk" patients who have already survived free of stroke for several years.

Genetic polymorphisms and personality in healthy adults: a systematic review and meta-analysis

A meta-analysis was conducted on studies reporting data on associations between candidate genes and human personality. Studies reporting data for psychiatric populations (including organic disease and substance abuse) were excluded. A total of 46 studies contributed to the analysis. Pooled data using a fixed-effects model suggested significant associations between the 5HTT LPR, DRD4 c>t, DRD4 length, DRD2 A1/A2, DRD3 A1/A2 polymorphisms and personality traits. A multivariate analysis using a mixed-effects model and including age, sex and predominant ethnicity as covariates was applied to the analyses of 5HTT LPR and DRD4 length polymorphism data. Only the association between the 5HTT LPR polymorphism and avoidance traits remained significant (P=0.038). However, sensitivity analyses excluding data from studies reporting allele frequencies not in Hardy-Weinberg equilibrium and unpublished data resulted in this association no longer being significant. Implications for the design of future association studies of human personality are discussed, including the likely sample sizes that will be required to achieve sufficient power and the potential role of moderating variables such as sex.

Gdf5 is expressed in the developing skeleton of median fins of late-stage zebrafish, Danio rerio

The dynamic expression of Gdf5 is described in the developing skeleton of the median fins of late-stage zebrafish, Danio rerio (6-45 days post-fertilization). In situ hybridization revealed expression in the mesenchyme between cartilage condensations of the endoskeletal supports of the dorsal, anal, and caudal fins. As development proceeds, the expression domains expand distally to surround tips of developing cartilages, consistent with a role in cartilage growth and differentiation. Gdf5 is later expressed in the segmenting regions of the dorsal and anal fin radials, which may indicate a role in segmentation. After growth to 7.5 mm, Gdf5 transcripts can no longer be detected in any of the median fins, nor is Gdf5 expression reinitiated in later development of the median fin skeleton.

A prognostic model for ovarian cancer

About 6000 women in the United Kingdom develop ovarian cancer each year and about two-thirds of the women will die from the disease. Establishing the prognosis of a woman with ovarian cancer is an important part of her evaluation and treatment. Prognostic models and indices in ovarian cancer should be developed using large databases and, ideally, with complete information on both prognostic indicators and long-term outcome. We developed a prognostic model using Cox regression and multiple imputation from 1189 primary cases of epithelial ovarian cancer (with median follow-up of 4.6 years). We found that the significant (P< or = 0.05) prognostic factors for overall survival were age at diagnosis, FIGO stage, grade of tumour, histology (mixed mesodermal, clear cell and endometrioid versus serous papillary), the presence or absence of ascites, albumin, alkaline phosphatase, performance status on the ZUBROD-ECOG-WHO scale, and debulking of the tumour. This model is consistent with other models in the ovarian cancer literature; it has better predictive ability and, after simplification and validation, could be used in clinical practice.

The I-antigens of Ichthyophthirius multifiliis are GPI-anchored proteins

The parasitic ciliate Ichthyophthirius multifiliis has abundant surface membrane proteins (i-antigens) that when clustered, trigger rapid, premature exit from the host. Similar antigens are present in free-living ciliates and are GPI-anchored in both Paramecium and Tetrahymena. Although transmembrane signalling through GPI-anchored proteins has been well-documented in metazoan cells, comparable phenomena have yet to be described in protists. Since premature exit of Ichthyophthirius is likely to involve a transmembrane signalling event, we sought to determine whether i-antigens are GPI-anchored in these cells as well. Based on their solubility properties in Triton X-114, the i-antigens of Ichthyophthirius are amphiphilic in nature and partition with the detergent phase. Nevertheless, following treatment of detergent lysates with phospholipase C, the same proteins become hydrophilic. Concomitantly, they are recognized by antibodies against a cross-reacting determinant exposed on virtually all GPI-anchored proteins following cleavage with phospholipase C. Finally, when expressed in recombinant form in Tetrahymena thermophila, full-length i-antigens are restricted to the membrane, while those lacking hydrophobic C-termini are secreted from the cell. Taken together, these observations argue strongly that the i-antigens of Ichthyophthirius multifiliis are, in fact, GPI-anchored proteins.

Spatiotemporal expression patterns of mammalian chordin during postgastrulation embryogenesis and in postnatal brain

Chordin is an antagonist of TGFbeta-like bone morphogenetic proteins (BMPs) that plays roles in dorsoventral axis formation and in induction, maintenance and/or differentiation of neural tissue in early vertebrate embryogenesis. In contrast, little is known concerning possible roles for Chordin at later stages of vertebrate development and in the adult. To provide insights into possible postgastrulation roles for Chordin, we report the spatiotemporal expression patterns of Chordin in 8.5- to 15.5-dpc mouse embryos and in the postnatal mouse brain. Expression of Chordin in the primordia of most major organs from 10.5 dpc, including the brain, lung, heart, liver, kidney, thymus, and gut, suggests multiple functions for Chordin in organogenesis, potentially by means of interactions with TGFbeta-like BMPs. The relatively high levels of Chordin expression in condensing and differentiating cartilage elements from 11.5 dpc indicates a generalized role for Chordin throughout embryonic skeletogenesis. In the postnatal mouse brain, we demonstrate that Chordin is coexpressed with other components of the TGFbeta-like BMP signalling pathway in the cerebellum and hippocampus, sites of high synaptic plasticity, suggesting a role for Chordin in this process.

Mammalian BMP-1/Tolloid-related metalloproteinases, including novel family member mammalian Tolloid-like 2, have differential enzymatic activities and distributions of expression relevant to patterning and skeletogenesis

Vertebrate bone morphogenetic protein 1 (BMP-1) and Drosophila Tolloid (TLD) are prototypes of a family of metalloproteases with important roles in various developmental events. BMP-1 affects morphogenesis, at least partly, via biosynthetic processing of fibrillar collagens, while TLD affects dorsal-ventral patterning by releasing TGFbeta-like ligands from latent complexes with the secreted protein Short Gastrulation (SOG). Here, in a screen for additional mammalian members of this family of developmental proteases, we identify novel family member mammalian Tolloid-like 2 (mTLL-2) and compare enzymatic activities and expression domains of all four known mammalian BMP-1/TLD-like proteases [BMP-1, mammalian Tolloid (mTLD), mammalian Tolloid-like 1 (mTLL-1), and mTLL-2]. Despite high sequence similarities, distinct differences are shown in ability to process fibrillar collagen precursors and to cleave Chordin, the vertebrate orthologue of SOG. As previously demonstrated for BMP-1 and mTLD, mTLL-1 is shown to specifically process procollagen C-propeptides at the physiologically relevant site, while mTLL-2 is shown to lack this activity. BMP-1 and mTLL-1 are shown to cleave Chordin, at sites similar to procollagen C-propeptide cleavage sites, and to counteract dorsalizing effects of Chordin upon overexpression in Xenopus embryos. Proteases mTLD and mTLL-2 do not cleave Chordin. Differences in enzymatic activities and expression domains of the four proteases suggest BMP-1 as the major Chordin antagonist in early mammalian embryogenesis and in pre- and postnatal skeletogenesis.

The mammalian Tolloid-like 1 gene, Tll1, is necessary for normal septation and positioning of the heart

Mammalian Tolloid-like 1 (mTLL-1) is an astacin-like metalloprotease, highly similar in domain structure to the morphogenetically important proteases bone morphogenetic protein-1 (BMP-1) and Drosophila Tolloid. To investigate possible roles for mTLL-1 in mammalian development, we have used gene targeting in ES cells to produce mice with a disrupted allele for the corresponding gene, Tll1. Homozygous mutants were embryonic lethal, with death at mid-gestation from cardiac failure and a unique constellation of developmental defects that were apparently confined solely to the heart. Constant features were incomplete formation of the muscular interventricular septum and an abnormal and novel positioning of the heart and aorta. Consistent with roles in cardiac development, Tll1 expression was specific to precardiac tissue and endocardium in 7.5 and 8.5 days p.c. embryos, respectively. Tll1 expression was also high in the developing interventricular septum, where expression of the BMP-1 gene, Bmp1, was not observed. Cardiac structures that were not affected in Tll1−/− embryos either showed no Tll1 expression (atrio-ventricular cushions) or showed overlapping expression of Tll1 and Bmp1 (aortico-pulmonary septum), suggesting that products of the Bmp1 gene may be capable of functionally substituting for mTLL-1 at sites in which they are co-expressed. Together, the various data show that mTLL-1 plays multiple roles in formation of the mammalian heart and is essential for formation of the interventricular septum.

Surface display of a parasite antigen in the ciliate Tetrahymena thermophila

The ciliated protozoan, Tetrahymena thermophila, offers an attractive medium for the expression of heterologous proteins and could prove particularly useful for the display of foreign proteins on the cell surface. Although progress has been made in transformation of Tetrahymena with heterologous DNA, methods that permit reliable expression of foreign genes have been lacking. Using a mutant strain of T. thermophila carrying a negatively selectable allele of a beta-tubulin gene, we have been able to direct foreign genes to this locus by homologous recombination. Transformed cell lines producing foreign proteins were readily identified and, in at least one case, targeting of proteins to the plasma membrane was accomplished.

The gene for an abundant parasite coat protein predicts tandemly repetitive metal binding domains

Immobilization antigens are highly abundant surface membrane proteins that coat the surface of hymenostomatid ciliates. While their function is unknown, recent studies with the common fish parasite, Ichthyophthirius multifiliis, suggest their involvement in a novel mechanism of humoral immunity involving an effect of antibody on parasite behavior. To gain further insight into the nature of these proteins, we have cloned a gene encoding the 48kDa i-antigen of I. multifiliis. Analysis of the gene (designated IAG48[G1]) reveals a single, uninterrupted reading frame that predicts a protein of 442 amino acids. Based on its deduced amino acid sequence, the protein contains hydrophobic amino acid domains at its N- and C-terminus that are characteristic of signal peptide and GPI-anchor addition sites, respectively. The most striking feature of the predicted protein, however, is a series of tandem repeats that spans most of its length. The repeats themselves are characterized by periodic cysteine residues that fall into register when the homologous segments are aligned. Interestingly, the spacing of cysteines (C-X2,3-C) within a framework of larger (C-X2-C-X20-C-X3-C-X20-C-X2-C) motifs is entirely consistent with the structure of known zinc-binding proteins. Finally, comparison of the coding sequence of the 48kDa i-antigen gene with a partial cDNA previously thought to encode this protein reveals nearly complete identity except at their 3' ends, suggesting that alternative forms of the antigen exist.

Structural organization and expression patterns of the human and mouse genes for the type I procollagen COOH-terminal proteinase enhancer protein

The procollagen C-proteinase enhancer (PCPE) is a glycoprotein that potentiates enzymatic cleavage of the type I procollagen C-propeptide by bone morphogenetic protein-1 (BMP-1). The human PCPE gene (PCOLCE) was previously mapped to 7q22, an area frequently disrupted in uterine leiomyomata, while disruption of the rat PCPE gene leads to anchorage-independent growth and loss of contact inhibition in rat fibroblasts. Here we describe the entire intron/exon organizations of PCOLCE and the mouse PCPE gene (Pcolce) and analyze expression of PCOLCE RNA in various human adult and fetal tissues and of Pcolce RNA at various stages of mouse development. PCOLCE and Pcolce are shown to be small genes 6.0 and 6.5 kb, respectively, with a conserved intron/exon structure comprising 9 exons. A notable difference between the two genes derives from insertion of multiple Alu sequences immediately upstream and downstream and within PCOLCE. Temporal expression of PCPE mRNA is shown to differ from that of BMP-1 and type I procollagen during mouse development, consistent with possible additional functions for PCPE beyond enhancement of C-proteinase activity. Consistent with a possible role in leiomyomata, PCOLCE is shown to be expressed at relatively high levels in uterus.

Staff attitudes about the use of robots in pharmacy before implementation of a robotic dispensing system

Hospital pharmacy staff members at a Mid-western university medical center were surveyed to determine their attitudes about the use of robots in pharmacy dispensing before a robotic system was implemented. A questionnaire seeking attitudes about the use of robots in pharmacy was distributed to 147 pharmacy staff (pharmacy managers, pharmacist practitioners, pharmacotherapists, pharmacy residents and fellows, pharmacy technicians, and salaried pharmacy students). Attitudinal items were scored on a 5-point scale ranging from very favorable to very unfavorable. The response rate was 75%. Overall, staff expressed favorable attitudes in terms of job security, professional impact, and general robotics orientation. Pharmacy managers and pharmacotherapists were the most likely to report feeling secure about their jobs; pharmacy technicians and salaried pharmacy students were slightly less positive. Favorable attitudes about the professional impact of the robotic system were demonstrated by all groups except pharmacist practitioners and pharmacy technicians. Attitudes about management issues were unfavorable; pharmacist practitioners demonstrated the least favorable attitudes. In general, responses to semantic-differential statements reflected favorable attitudes; where there were differences, pharmacy technicians showed the least positive and pharmacy managers the most positive attitudes. Respondents reported that pharmacist practitioners would be most positively affected and pharmacy technicians most negatively affected by robotic dispensing. Almost half of the respondents who provided general comments indicated that they needed more information about the use of robots. Pharmacy staff had generally favorable attitudes about the use of robots in pharmacy.

Coding sequence and expression patterns of mouse chordin and mapping of the cognate mouse chrd and human CHRD genes

Chordin is a key developmental protein that dorsalizes early vertebrate embryonic tissues by binding to ventralizing TGF-beta-like bone morphogenetic proteins and sequestering them in latent complexes. Here we report the first characterization of mammalian chordin. The full-length cDNA sequence for mouse chordin is given, and RNA blot analysis shows the murine chordin gene Chrd to be expressed at relatively high levels in 7-day postcoitum mouse embryos and at much decreased levels at later developmental times and in adult tissues. These results imply a major role for chordin during gastrulation of the mammalian embryo. Nevertheless, both murine and human chordin genes are shown to be expressed at readily detectable levels in several fetal and adult tissues, most notably liver and cerebellum, suggesting additional roles in organogenesis and homeostasis. Chrd was mapped to mouse chromosome 16 using interspecific crosses, and the cognate human gene CHRD was localized to human chromosome 3q27 by radiation hybrid mapping.

Antibody-mediated effects on parasite behavior: Evidence of a novel mechanism of immunity against a parasitic protist

The parasitic ciliate Ichthyophthirius multifiliis is well known in commercial aquaculture as the etiological agent of 'white spot', a disease that afflicts a wide range of fresh-water fish. While Ichthyophthirius is highly pathogenic, animals exposed to controlled infections develop a strong acquired resistance to the parasite. Recent studies suggest host resistance involves a novel mechanism of humoral immunity affecting parasite behavior. Rather than being killed, parasites are forced to exit fish prematurely in response to antibody binding. The target antigens involved in this process are a class of highly abundant glycosylphosphatidyl-inositol-anchored coat proteins referred to as immobilization antigens, or i-antigens. Here, Theodore Clark and Harry Dickerson describe this phenomenon and offer a number of hypotheses that could account for the forced exit.

Passive immunization of channel catfish (Ictalurus punctatus) against the ciliated protozoan parasite Ichthyophthirius multifiliis by use of murine monoclonal antibodies

Fish acquire immunity against the ciliated protozoan parasite Ichthyophthirius multifiliis following sublethal infection. The immune response includes the elaboration of humoral antibodies against a class of abundant surface membrane proteins referred to as immobilization antigens (i-antigens). Antibodies against these proteins immobilize the parasite in vitro, suggesting a potential role for the i-antigens in protective immunity. To test this hypothesis, passive immunization experiments were carried out with naive channel catfish, Ictalurus punctatus, using immobilizing murine monoclonal antibodies (MAbs). Fish were completely protected against lethal challenge following intraperitoneal injection of 20 to 200 micrograms of MAb. Although fish succumbed to infection at lower doses, palliative effects were observed with as little as 2 micrograms of antibody. In experiments in which animals were challenged at various times following inoculation, an inverse relationship between parasite load and serum immobilizing activity was seen. Of seven MAbs which conferred protection, all were immunoglobulin G class antibodies. The only immobilizing MAb that failed to protect was an immunoglobulin M antibody that was absent from surface mucosa as determined by enzyme-linked immunosorbent assay. The implications of these findings for the development of a vaccine against I. multifiliis and immunity against surface pathogens of fish are discussed.

Surface antigen cross-linking triggers forced exit of a protozoan parasite from its host

We used the common fish pathogen Ichthyophthirius multifiliis as a model for studying interactions between parasitic ciliates and their vertebrate hosts. Although highly pathogenic, Ichthyophthirius can elicit a strong protective immune response in fish after exposure to controlled infections. To investigate the mechanisms underlying host resistance, a series of passive immunization experiments were carried out using mouse monoclonal antibodies against a class of surface membrane proteins, known as immobilization antigens (or i-antigens), thought to play a role in the protective response. Such antibodies bind to cilia and immobilize I. multifiliis in vitro. Surprisingly, we found that passive antibody transfer in vivo caused rapid exit of parasites from the host. The effect was highly specific for a given I. multifiliis serotype. F(ab)2 subfragments had the same effect as intact antibody, whereas monovalent Fab fragments failed to protect. The activity of Fab could, nevertheless, be restored after subsequent i.p. injection of bivalent goat anti-mouse IgG. Parasites that exit the host had detectable antibody on their surface and appeared viable in all respects. These findings represent a novel instance among protists in which protective immunity (and evasion of the host response) result from an effect of antibody on parasite behavior.

An improved method for isolating RNA from coccidian oocysts

A method, based on the disruption of eimerian oocysts in a French pressure cell in the presence of guanidine isothiocyanate, has been developed to isolate large quantities of high quality total RNA efficiently. This procedure results in a 12.5-fold greater number of oocysts broken, and a 22-fold greater yield of total RNA than from disruption by conventional grinding in liquid N2. In addition, the RNA isolated by the French pressure cell method was of equal or superior quality when compared to RNA isolated by grinding. This procedure provides a significant improvement in RNA extraction from eimerian oocysts and will greatly facilitate the study of gene expression in this important group of parasites.

Developmental regulation of an Eimeria bovis mRNA encoding refractile body-associated proteins

Eimeria bovis antigens defined by the monoclonal antibody (mAb) 2.4 are associated with the refractile bodies of sporozoites and are found in the parasitophorous vacuole and host cell cytoplasm during schizogony. Screening of an E. bovis oocyst cDNA library with mAb 2.4 resulted in the identification of a single unique cDNA sequence (Eb-25/50). Comparison of the predicted protein sequence of Eb-25/50 revealed a high degree of identity to an Eimeria tenella refractile body protein and mAb 2.4 was found to cross-react with refractile bodies from Eimeria acervulina, demonstrating that these proteins are highly conserved among eimerian species. Measurements of Eb-25/50 mRNA showed that the multiple proteins recognized by mAb 2.4 are encoded by a single mRNA species whose kinetics of expression during sporulation and schizogony closely correlated with protein expression. Consistent with multiple Eb-25/50 proteins arising from a single polypeptide, results from a Southern analysis of E. bovis genomic DNA indicated that Eb-25/50 mRNA is derived from a single copy gene. The presence of Eb-25/50 proteins in the host cytoplasm during schizogony, the high degree of conservation of these proteins, and the apparent complex post-translational modification raises interesting questions about the biochemistry of these proteins during eimerian development.

Serotypic variation among isolates of Ichthyophthirius multifiliis based on immobilization

Efforts have been made to determine whether surface antigens could be used as biochemical markers to define strain differences in the parasitic ciliate Ichthyophthirius multifiliis. In previous studies, a wild-type isolate designated G1 was found to have surface proteins analogous to the immobilization antigens of Paramecium and Tetrahymena; rabbit antiserum against this strain immobilizes homologous cells in vitro. It has now been shown for two additional Ichthyophthirius isolates (designated G1.1 and G2) that immobilization antigens are both present and serologically distinct. Proteins of similar size, which cross-react in Western blots with rabbit antisera against immobilization antigens of the G1 strain, are nevertheless found in the G1.1 and G2 isolates. As shown by Southern blotting analysis, the G1.1 and G2 strains also contain genomic DNA sequences which hybridize with an immobilization antigen cDNA from G1 when probed under conditions of reduced stringency. The serotypic differences in immobilization between I. multifiliis isolates appear to be stable over time and provide a means of discriminating strains. In addition to providing a basis for comparative studies, the work described here has implications for the development of vaccines against this important fish parasite.

Developmental gene expression in Eimeria bovis

By differential screening of stage-specific cDNA libraries of Eimeria bovis, we have identified and isolated a large set of genes that are regulated during development of the sporozoites and merozoites. Duplicate lifts of cDNA libraries constructed from partially sporulated oocysts and merozoites were probed with radioactively labeled first-strand cDNA prepared from partially sporulated oocyst and merozoite mRNA. Out of 60,000 plaques screened in each case, over 250 plaques from the partially sporulated oocyst library preferentially hybridized with the oocyst cDNA probe and 67 plaques from the merozoite library preferentially hybridized with the merozoite cDNA probe. Three of the oocyst phage and 7 of the merozoite phage were selected for further characterization. Northern analysis revealed a common pattern of mRNA expression for the oocyst cDNA clones. Consistent with the results of the differential screen, no hybridization to merozoite RNA was detected with any of these 3 oocyst cDNA clones. The expression of the merozoite cDNA clones was more complex, with 3 different classes of merozoite genes being identified based on their pattern of developmental regulation. Although each of the merozoite clones was expressed to some extent during sporulation, in all cases, expression was higher in merozoites than in partially sporulated oocysts, consistent with the restriction of expression defined by the differential screen. Sequence analysis revealed that 2 of the merozoite cDNA clones encode elongation factor 1 alpha and the ubiquitin/ribosomal protein fusion, and 1 of the sporozoite cDNAs displays a significant identity to insulin-degrading enzyme. The developmental expression of E. bovis genes involved in protein synthesis and degradation provides additional evidence for the importance of regulation of protein metabolism during parasite development.

Developmental expression of surface antigen genes in the parasitic ciliate Ichthyophthirius multifiliis

A 1.2-kilobase (kb) cDNA encoding a major surface antigen of the holotrich ciliate Ichthyophthirius multifiliis (an obligate parasite of fish) has been isolated and used as a probe to examine the expression of immobilization antigen (i-antigen) genes in this system. The cDNA encodes a predicted protein of 394 amino acids with a tandemly repeated structure characteristic of the i-antigens of the related free-living ciliates Paramecium and Tetrahymena. As shown by Northern hybridization analysis with both total and poly(A)+ RNAs, the 1.2-kb cDNA recognizes distinct transcripts of 1.6 and 1.9 kb which are differentially expressed through the parasite life cycle. During the transition from the host-associated trophozoite stage to the infective tomite stage, steady-state levels of the 1.9-kb RNA undergo a marked increase of greater than or equal to 50-fold, while the 1.6-kb transcript increases only slightly. The absolute amounts of RNA encoding the i-antigen have been quantitated and were found to reach extremely high levels equivalent to approximately 6% of the poly(A)+ RNA of I. multifiliis tomites. Southern hybridization analysis with I. multifiliis genomic DNA suggests that at least two genes encode the i-antigen transcripts. In experiments to examine the effects of temperature on the expression of I. multifiliis i-antigen genes, levels of the 1.6- and 1.9-kb transcripts were found to remain relatively constant in cells maintained at different temperature extremes. These studies indicate that genes encoding i-antigens of I. multifiliis are developmentally regulated, and they suggest the existence of alternative mechanisms for the control of surface antigen expression in ciliates.

A bovine homolog to the human myogenic determination factor myf-5: sequence conservation and 3' processing of transcripts

A bovine cDNA library from fetal skeletal muscle myoblasts. was screened with a 274 bp probe to a conserved region of the mouse MyoD1 cDNA. One positive recombinant, designated bmyf, was found to contain a 1931 bp insert with an open reading frame encoding a predicted protein highly related to the human myogenic factor myf-5 Human and bovine factors are 96% homologous in their predicted amino acid sequences. At the nucleotide level, bmyf and myf-5 are 92% identical in the coding region and 74 and 80% homologous in their 5'- and 3'-untranslated regions, respectively. The bmyf cDNA, nevertheless, extends 475 nucleotides beyond a polyadenylation signal common to both cDNAs. Bmyf transcripts are expressed exclusively in skeletal muscle where three transcripts of 1.5, 2 and 3 kb were detected. While the 1.5 kb transcript lacks sequences 3' to the polyadenylation signal at nt 1415 in the bmyf cDNA, both the 2 and 3 kb RNAs contain these sequences suggesting that bmyf transcripts are alternatively polyadenylated. Bmyf cDNA can activate the expression of the myogenic program in C3H10T1/2 fibroblasts as assayed by stable and transient transfection experiments.

Icthyophthirius multifiliis has membrane-associated immobilization antigens

Sera from fish that survive infections with the ciliated protozoon, Ichthyophthirius multifiliis, immobilize the parasite in vitro. In order to identify cell surface antigens involved in the immobilization response, integral membrane proteins were extracted from tomites with Triton X-114 and used to immunize rabbits. The rabbit antisera immobilized the parasite in vitro and antigens were localized to cell and ciliary plasma membranes by indirect immunofluorescent microscopy. The membrane protein fractions from both whole cells and tomite cilia were characterized by 1- and 2-dimensional SDS-PAGE. A 43,000-dalton (D) glycoprotein with an isoelectric point of 7.0 is the predominant protein in these fractions, comprising 12% and 60% of the total protein of whole cell and ciliary membranes, respectively. Western blot analysis of ciliary proteins with immune rabbit sera indicated that the 43,000-D glycoprotein is the principal antigen.

Energy requirements for pigment aggregation in fundulus melanophores

Teleost chromatophores are filled with individual pigment granules that rapidly aggregate to the cell center or become dispersed throughout the cytoplasm in response to environmental stimuli. Microtubules appear to be required for pigment aggregation (movement toward the cell center), and recent findings have suggested that a dynein-like ATPase may participate in force production. Based on previous studies, however, it has been argued that pigment aggregation does not require energy directly, a view that supports the involvement of an elastic component in granule movement. To examine this point further, we have reinvestigated the energy requirements for pigment aggregation using both intact cells and detergent-permeabilized cell models of Fundulus melanophores. Poisons of oxidative phosphorylation, namely, 2,4 dinitrophenol and NaCN, reversibly inhibit melanosome aggregation in response to adrenaline. Inhibition of movement results directly from depletion of intracellular ATP, since pigment translocation can be reactivated in permeabilized cells by the addition of exogenous ATP to the lysis buffer. Non-hydrolyzable analogues, including beta, gamma-imidoadenosine-5'-triphosphate (AMPPNP), beta, gamma-methylene adenosine-5'-triphosphate (AMPPCP), and ATP gamma S, will not substitute for ATP in reactivation of movement. Similarly, other nucleotides such as ADP, AMP, GTP, CTP, and ITP, have limited ability to support melanosome aggregation in metabolically poisoned cells subjected to detergent lysis. ATP itself has no effect on intact cells. These results indicate that melanosome aggregation is ATP-dependent and energy-driven, and are consistent with a role for a force-transducing ATPase in particle movement.

Pigment particle translocation in detergent-permeabilized melanophores of Fundulus heteroclitus

Melanophore preparations of Fundulus heteroclitus that have been treated with the detergent Brij 58 can aggregate their pigment in response to epinephrine. On the basis of several criteria, it appears that cell lysis occurs under the detergent conditions used. Electron microscopic examination of detergent-treated cells shows progressive disruption of the melanophore plasma membrane during the time in which pigment aggregation occurs. Brij-treated cells are accessible to ferritin, a large electron-dense probe that is effectively excluded from non-detergent-treated controls. In cells incubated with detergent, fixed, and treated first with rat monoclonal antibodies against tubulin and then with fluorescein-isothiocyanate-labeled goat anti-rat IgG, a characteristic radical pattern of microtubule staining can be visualized by fluorescence microscopy. Control preparations treated similarly, but without detergent, do not stain. Vanadate, an inhibitor of ciliary and flagellar dynein ATPase, blocks melanosome aggregation in response to epinephrine in detergent-treated preparations but has no effect on intact melanophores. erythro-9-[3-(2-hydroxynonyl)]Adenine, another inhibitor of dynein ATPase, also inhibits pigment aggregation in Fundulus melanophores. The possibility that a dynein-like molecule plays a role in pigment aggregation is discussed.

An actin filament matrix in hand-isolated nuclei of X. laevis oocytes

The nuclear gel of Xenopus oocytes contains a meshwork of randomly oriented microfilaments which have been identified as F-actin by decoration with rabbit skeletal muscle myosin subfragment-1 (S-1). Nuclear gel preparations treated with S-1 differ in several respects from control preparations incubated in either aqueous medium alone, or medium containing BSA. Actin filaments in control preparations appear less well preserved than those in S-1 treated preparations of the nuclear gel. The nucleoli of control preparations are extremely dense, while those of S-1 treated preparations have a more open, granular appearance. Large granular aggregates, which are a prominent feature of the controls, are seen much less frequently in S-1-treated preparations of the nuclear gel. These morphological differences appear to be correlated with the binding of protein to F-actin, since nuclear gel preparations incubated in tropomyosin, which also binds to actin filaments, appear similar to those treated with S-1. Approximately 63% of the total nuclear actin exists in a globular state, while 37% is filamentous.

Actin in Xenopus oocytes

It has been found that a high-speed supernatant fraction from Xenopus oocytes extracted in the cold will form a clear, solid gel upon warming. Gel formation occurs within 60 min at 18 degrees-40 degrees C, and is, at least initially, temperature reversible. Gelation is strictly dependent upon the addition of sucrose to the extraction medium. When isolated in the presence of ATP, the gel consists principally of a 43,000-dalton protein which co-migrates with Xenopus skeletal muscle actin on SDS-polyacrylamide gels, and a prominent high molecular weight component of approx. 250,000 daltons. At least two minor components of intermediate molecular weight are also found associated with the gel in variable quantities. Actin has been identified as the major consituent of the gel by ultrastructural and immunological techniques, and comprises roughly 47% of protein in the complex. With time, the gel spontaneously contracts to form a small dense aggregate. Contraction requires ATP. In the absence of exogenous ATP, a polypeptide which co-migrates with the heavy chain of Xenopus skeletal muscle myosin becomes a prominent component of the gel. This polypeptide is virtually absent from gels which have contracted in ATP-containing extracts. It has also been found that Ca++ is required for gelation in oocyte extracts. At both low and high concentrations of Ca++ (defined as a ratio of Ca++/EGTA in the extraction medium), gelation is inhibited.

Actin in Xenopus oocytes. II. Intracellular distribution and polymerizability

The largest oocytes of Xenopus Laevis were broken open in the absence of shearing forces which might transfer actin from particulate to supernatant fractions. Particulate and postmitochondrial supernatant fractions were prepared by centrifugation. SDS-electrophoretic fractionation on polyacrylamide gels and quantitative scanning techniques were used to separate actin and to assay its amount in cellular fractions. The actin has been identified in electrophoretograms by its molecular weight and its binding to DNase I. oocytes contain 1.4-1.7 {um}g of actin per cell, of which up to 88 percent is recovered in the postmitochondrial supernate under a variety of conditions. In the soluble fraction, it represents about 8.8 percent of the total protein. Its concentration in native cytoplasm was directly assayed at 4.1 mg/ml. There is no detectable actin that can be transferred from the particulate to the soluble phase by neutral detergents or ionic conditions that would depolymerize muscle actin. Centrifugation of the soluble oocyte fractions showed that 75-95 percent of the actin can not be sedimented under forces that would pellet filamentous actin. Addition of potassium and magnesium to the cytoplasm, to concentrations that would polymerize muscle actin, does not increase the amount of sedimentable actin. Roughly one-third of the soluble actin is recovered from Sephadex columns at about the position of monomer. About two- thirds is in complexes of 100,000 daltons or greater.