Therapeutic administration of a cross-reactive mAb targeting the fusion glycoprotein of Nipah virus protects nonhuman primates

No licensed vaccines or therapies exist for patients infected with Nipah virus (NiV), although an experimental human monoclonal antibody (mAb) cross-reactive to the NiV and Hendra virus (HeV) G glycoprotein, m102.4, has been tested in a phase 1 trial and has been provided under compassionate use for both HeV and NiV exposures. NiV is a highly pathogenic zoonotic paramyxovirus causing regular outbreaks in humans and animals in South and Southeast Asia. The mortality rate of NiV infection in humans ranges from 40% to more than 90%, making it a substantial public health concern. The NiV G glycoprotein mediates host cell attachment, and the F glycoprotein facilitates membrane fusion and infection. We hypothesized that a mAb against the prefusion conformation of the F glycoprotein may confer better protection than m102.4. To test this, two potent neutralizing mAbs against NiV F protein, hu1F5 and hu12B2, were compared in a hamster model. Hu1F5 provided superior protection to hu12B2 and was selected for comparison with m102.4 for the ability to protect African green monkeys (AGMs) from a stringent NiV challenge. AGMs were exposed intranasally to the Bangladesh strain of NiV and treated 5 days after exposure with either mAb (25 milligrams per kilogram). Whereas only one of six AGMs treated with m102.4 survived until the study end point, all six AGMs treated with hu1F5 were protected. Furthermore, a reduced 10 milligrams per kilogram dose of hu1F5 also provided complete protection against NiV challenge, supporting the upcoming clinical advancement of this mAb for postexposure prophylaxis and therapy.

Efficacy and Safety Outcomes of Cataract Surgery in Survivors of Ebola Virus Disease: 12-Month Results From the PREVAIL VII Study

Purpose

In survivors of Ebola virus disease (EVD), intraocular viral persistence raises questions about the timing and safety of cataract surgery. To the best of our knowledge, this is the first controlled study evaluating Ebola virus persistence and cataract surgery safety and outcomes in EVD survivors.

Methods

Seropositive EVD survivors and seronegative controls with vision worse than 20/40 from cataract and without active intraocular inflammation were enrolled. Aqueous humor from survivors was tested with reverse transcription-polymerase chain reaction for Ebola viral RNA. Participants underwent manual small-incision cataract surgery and 1 year of follow-up examinations.

Results

Twenty-two eyes of 22 survivors and 12 eyes of eight controls underwent cataract surgery. All of the aqueous samples tested negative for Ebola viral RNA. Median visual acuity improved from 20/200 at baseline to 20/25 at 1 year in survivors and from count fingers to 20/50 in controls (overall, P < 0.001; between groups, P = 0.07). After a 1-month course of topical corticosteroids, 55% of survivors and 67% of controls demonstrated at least 1+ anterior chamber cell. Twelve months after surgery, optical coherence tomography revealed a median increase in macular central subfield thickness of 42 µm compared with baseline (overall, P = 0.029; between groups, P = 0.995).

Conclusions

EVD survivors and controls demonstrated significant visual improvement from cataract surgery. The persistence of intraocular inflammation highlights the importance of follow-up. The absence of detectable intraocular Ebola viral RNA provides guidance regarding the safety of eye surgery in Ebola survivors.

Translational Relevance

These findings demonstrate the safety and efficacy of cataract surgery in Ebola survivors and will inform ocular surgery guidelines in this population.

Ebola Virus Neutralizing Antibodies Detectable in Survivors of theYambuku, Zaire Outbreak 40 Years after Infection

The first reported outbreak of Ebola virus disease occurred in 1976 in Yambuku, Democratic Republic of Congo. Antibody responses in survivors 11 years after infection have been documented. However, this report is the first characterization of anti-Ebola virus antibody persistence and neutralization capacity 40 years after infection. Using ELISAs we measured survivor’s immunological response to Ebola virus Zaire (EBOV) glycoprotein and nucleoprotein, and assessed VP40 reactivity. Neutralization of EBOV was measured using a pseudovirus approach and plaque reduction neutralization test with live EBOV. Some survivors from the original EBOV outbreak still harbor antibodies against all 3 measures. Interestingly, a subset of these survivors’ serum antibodies could still neutralize live virus 40 years postinitial infection. These data provide the longest documentation of both anti-Ebola serological response and neutralization capacity within any survivor cohort, extending the known duration of response from 11 years postinfection to at least 40 years after symptomatic infection.

Pan-Filovirus Serum Neutralizing Antibodies in a Subset of Congolese Ebolavirus Infection Survivors

One year after a Zaire ebolavirus (EBOV) outbreak occurred in the Boende Health Zone of the Democratic Republic of the Congo during 2014, we sought to determine the breadth of immune response against diverse filoviruses including EBOV, Bundibugyo (BDBV), Sudan (SUDV), and Marburg (MARV) viruses. After assessing the 15 survivors, 5 individuals demonstrated some degree of reactivity to multiple ebolavirus species and, in some instances, Marburg virus. All 5 of these survivors had immunoreactivity to EBOV glycoprotein (GP) and EBOV VP40, and 4 had reactivity to EBOV nucleoprotein (NP). Three of these survivors showed serologic responses to the 3 species of ebolavirus GPs tested (EBOV, BDBV, SUDV). All 5 samples also exhibited ability to neutralize EBOV using live virus, in a plaque reduction neutralization test. Remarkably, 3 of these EBOV survivors had plasma antibody responses to MARV GP. In pseudovirus neutralization assays, serum antibodies from a subset of these survivors also neutralized EBOV, BDBV, SUDV, and Taï Forest virus as well as MARV. Collectively, these findings suggest that some survivors of naturally acquired ebolavirus infection mount not only a pan-ebolavirus response, but also in less frequent cases, a pan-filovirus neutralizing response.

Use of the Filovirus Animal Non-Clinical Group (FANG) Ebola virus immuno-assay requires fewer study participants to power a study than the Alpha Diagnostic International assay

As part of the scientific community's development of medical countermeasures against Ebola virus disease, optimization of standardized assays for product evaluation is paramount. The recent outbreak heightened awareness to the scarcity of available assays and limited information on performance and reproducibility. To evaluate the immunogenicity of vaccines entering Phase I-III trials and to identify survivors, two enzyme-linked immunosorbent assays, the Filovirus Animal Non-Clinical Group assay and the Alpha Diagnostics International assay, were evaluated for detection of immunoglobulin G against Ebola virus glycoprotein. We found that the Filovirus Animal Nonclinical Group assay produced a wider range of relative antibody concentrations, higher assay precision, larger relative accuracy range, and lower regional background. Additionally, to sufficiently power a vaccine trial, use of the Filovirus Animal Nonclinical Group assay would require one third the number of participants than the Alpha Diagnostics International assay. This reduction in needed study participants will require less money, fewer man hours, and much less time to evaluate vaccine immunogenicity.

Detection of Ebola Virus RNA Through Aerosol Sampling of Animal Biosafety Level 4 Rooms Housing Challenged Nonhuman Primates

Ebola virus disease is a serious illness of humans and nonhuman primates (NHPs). Direct contact has been shown to be the primary source of Ebola (EBOV) transmission. We used a high-volume air sampler to determine whether EBOV could be detected during 3 independent studies with EBOV-challenged NHPs. Viral RNA was recovered during days 9 and 10 of Study I and days 7 and 8 of Study III. Viral RNA levels were below limits of detection during all other collections. The results demonstrate that the biosafety level 4 (BSL-4) suit protects workers from aerosols in a BSL-4 environment using proper engineering and administrative controls.

Assessment and Optimization of the GeneXpert Diagnostic Platform for Detection of Ebola Virus RNA in Seminal Fluid

Recent studies have suggested that Ebola virus (EBOV) ribonucleic acid (RNA) potentially present in the semen of a large number of survivors of Ebola virus disease (EVD) in Western Africa may contribute to sexual transmission of EVD and generate new clusters of cases in regions previously declared EVD-free. These findings drive the immediate need for a reliable, rapid, user-friendly assay for detection of EBOV RNA in semen that is deployable to multiple sites across Western Africa. In this study, we optimized the Xpert EBOV assay for semen samples by adding dithiothreitol. Compared to the assays currently in use in Liberia (including Ebola Zaire Target 1, major groove binder real-time-polymerase chain reaction assays, and original Xpert EBOV assay), the modified Xpert EBOV assay demonstrated greater sensitivity than the comparator assays. Thus, the modified Xpert EBOV assay is optimal for large-scale monitoring of EBOV RNA persistence in male survivors.

Lateral Flow Immunoassays for Ebola Virus Disease Detection in Liberia

BACKGROUND

Lateral flow immunoassays (LFIs) are point-of-care diagnostic assays that are designed for single use outside a formal laboratory, with in-home pregnancy tests the best-known example of these tests. Although the LFI has some limitations over more-complex immunoassay procedures, such as reduced sensitivity and the potential for false-positive results when using complex sample matrices, the assay has the benefits of a rapid time to result and ease of use. These benefits make it an attractive option for obtaining rapid results in an austere environment. In an outbreak of any magnitude, a field-based rapid diagnostic assay would allow proper patient transport and for safe burials to be conducted without the delay caused by transport of samples between remote villages and testing facilities. Use of such point-of-care instruments in the ongoing Ebola virus disease (EVD) outbreak in West Africa would have distinct advantages in control and prevention of local outbreaks, but proper understanding of the technology and interpretation of results are important.

METHODS

In this study, a LFI, originally developed by the Naval Medical Research Center for Ebola virus environmental testing, was evaluated for its ability to detect the virus in clinical samples in Liberia. Clinical blood and plasma samples and post mortem oral swabs submitted to the Liberian Institute for Biomedical Research, the National Public Health Reference Laboratory for EVD testing, were tested and compared to results of real-time reverse transcription-polymerase chain reaction (rRT-PCR), using assays targeting Ebola virus glycoprotein and nucleoprotein.

RESULTS

The LFI findings correlated well with those of the real-time RT-PCR assays used as benchmarks.

CONCLUSIONS

Rapid antigen-detection tests such as LFIs are attractive alternatives to traditional immunoassays but have reduced sensitivity and specificity, resulting in increases in false-positive and false-negative results. An understanding of the strengths, weaknesses, and limitations of a particular assay lets the diagnostician choose the correct situation to use the correct assay and properly interpret the results.

Development, Evaluation, and Integration of a Quantitative Reverse-Transcription Polymerase Chain Reaction Diagnostic Test for Ebola Virus on a Molecular Diagnostics Platform

BACKGROUND

The 2013-2016 Ebola epidemic in West Africa resulted in accelerated development of rapid diagnostic tests for emergency outbreak preparedness. We describe the development and evaluation of the Idylla™ prototype Ebola virus test, a fully automated sample-to-result molecular diagnostic test for rapid detection of Zaire ebolavirus (EBOV) and Sudan ebolavirus (SUDV).

METHODS

The Idylla™ prototype Ebola virus test can simultaneously detect EBOV and SUDV in 200 µL of whole blood. The sample is directly added to a disposable cartridge containing all reagents for sample preparation, RNA extraction, and amplification by reverse-transcription polymerase chain reaction analysis. The performance was evaluated with a variety of sample types, including synthetic constructs and whole blood samples from healthy volunteers spiked with viral RNA, inactivated virus, and infectious virus.

RESULTS

The 95% limits of detection for EBOV and SUDV were 465 plaque-forming units (PFU)/mL (1010 copies/mL) and 324 PFU/mL (8204 copies/mL), respectively. In silico and in vitro analyses demonstrated 100% correct reactivity for EBOV and SUDV and no cross-reactivity with relevant pathogens. The diagnostic sensitivity was 97.4% (for EBOV) and 91.7% (for SUDV), the specificity was 100%, and the diagnostic accuracy was 95.9%.

CONCLUSIONS

The Idylla™ prototype Ebola virus test is a fast, safe, easy-to-use, and near-patient test that meets the performance criteria to detect EBOV in patients with suspected Ebola.

3B11-N, a monoclonal antibody against MERS-CoV, reduces lung pathology in rhesus monkeys following intratracheal inoculation of MERS-CoV Jordan-n3/2012

Middle East Respiratory Syndrome Coronavirus (MERS-CoV) was identified in 2012 as the causative agent of a severe, lethal respiratory disease occurring across several countries in the Middle East. To date there have been over 1600 laboratory confirmed cases of MERS-CoV in 26 countries with a case fatality rate of 36%. Given the endemic region, it is possible that MERS-CoV could spread during the annual Hajj pilgrimage, necessitating countermeasure development. In this report, we describe the clinical and radiographic changes of rhesus monkeys following infection with 5×10⁶ PFU MERS-CoV Jordan-n3/2012. Two groups of NHPs were treated with either a human anti-MERS monoclonal antibody 3B11-N or E410-N, an anti-HIV antibody. MERS-CoV Jordan-n3/2012 infection resulted in quantifiable changes by computed tomography, but limited other clinical signs of disease. 3B11-N treated subjects developed significantly reduced lung pathology when compared to infected, untreated subjects, indicating that this antibody may be a suitable MERS-CoV treatment.

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MERS-CoV Jordan-n3/2012 challenge of rhesus monkeys results in a mild disease.

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CT can be used to monitor disease progression to aid models of human disease.

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Treatment with the human monoclonal antibody 3B11-N resulted in decreased disease.

Molecular Evidence of Sexual Transmission of Ebola Virus

A suspected case of sexual transmission from a male survivor of Ebola virus disease (EVD) to his female partner (the patient in this report) occurred in Liberia in March 2015. Ebola virus (EBOV) genomes assembled from blood samples from the patient and a semen sample from the survivor were consistent with direct transmission. The genomes shared three substitutions that were absent from all other Western African EBOV sequences and that were distinct from the last documented transmission chain in Liberia before this case. Combined with epidemiologic data, the genomic analysis provides evidence of sexual transmission of EBOV and evidence of the persistence of infective EBOV in semen for 179 days or more after the onset of EVD. (Funded by the Defense Threat Reduction Agency and others.).

Use of Existing Diagnostic Reverse-Transcription Polymerase Chain Reaction Assays for Detection of Ebola Virus RNA in Semen

Sexual transmission of Ebola virus in Liberia has now been documented and associated with new clusters in regions previously declared Ebola free. Assays that have Emergency Use Authorization (EUA) and are routinely used to detect Ebola virus RNA in whole blood and plasma specimens at the Liberian Institute for Biomedical Research were tested for their suitability in detecting the presence of Ebola virus RNA in semen. Qiagen AVL extraction protocols, as well as the Ebola Zaire Target 1 and major groove binder quantitative reverse-transcription polymerase chain reaction assays, were demonstrably suitable for this purpose and should facilitate epidemiologic investigations, including those involving long-term survivors of Ebola.

Monitoring of Ebola Virus Makona Evolution through Establishment of Advanced Genomic Capability in Liberia

To support Liberia's response to the ongoing Ebola virus (EBOV) disease epidemic in Western Africa, we established in-country advanced genomic capabilities to monitor EBOV evolution. Twenty-five EBOV genomes were sequenced at the Liberian Institute for Biomedical Research, which provided an in-depth view of EBOV diversity in Liberia during September 2014-February 2015. These sequences were consistent with a single virus introduction to Liberia; however, shared ancestry with isolates from Mali indicated at least 1 additional instance of movement into or out of Liberia. The pace of change is generally consistent with previous estimates of mutation rate. We observed 23 nonsynonymous mutations and 1 nonsense mutation. Six of these changes are within known binding sites for sequence-based EBOV medical countermeasures; however, the diagnostic and therapeutic impact of EBOV evolution within Liberia appears to be low.

Possible sexual transmission of Ebola virus - Liberia, 2015

On March 20, 2015, 30 days after the most recent confirmed Ebola Virus Disease (Ebola) patient in Liberia was isolated, Ebola was laboratory confirmed in a woman in Monrovia. The investigation identified only one epidemiologic link to Ebola: unprotected vaginal intercourse with a survivor. Published reports from previous outbreaks have demonstrated Ebola survivors can continue to harbor virus in immunologically privileged sites for a period of time after convalescence. Ebola virus has been isolated from semen as long as 82 days after symptom onset and viral RNA has been detected in semen up to 101 days after symptom onset. One instance of possible sexual transmission of Ebola has been reported, although the accompanying evidence was inconclusive. In addition, possible sexual transmission of Marburg virus, a filovirus related to Ebola, was documented in 1968. This report describes the investigation by the Government of Liberia and international response partners of the source of Liberia's latest Ebola case and discusses the public health implications of possible sexual transmission of Ebola virus. Based on information gathered in this investigation, CDC now recommends that contact with semen from male Ebola survivors be avoided until more information regarding the duration and infectiousness of viral shedding in body fluids is known. If male survivors have sex (oral, vaginal, or anal), a condom should be used correctly and consistently every time.

Filovirus RefSeq entries: evaluation and selection of filovirus type variants, type sequences, and names

Sequence determination of complete or coding-complete genomes of viruses is becoming common practice for supporting the work of epidemiologists, ecologists, virologists, and taxonomists. Sequencing duration and costs are rapidly decreasing, sequencing hardware is under modification for use by non-experts, and software is constantly being improved to simplify sequence data management and analysis. Thus, analysis of virus disease outbreaks on the molecular level is now feasible, including characterization of the evolution of individual virus populations in single patients over time. The increasing accumulation of sequencing data creates a management problem for the curators of commonly used sequence databases and an entry retrieval problem for end users. Therefore, utilizing the data to their fullest potential will require setting nomenclature and annotation standards for virus isolates and associated genomic sequences. The National Center for Biotechnology Information’s (NCBI’s) RefSeq is a non-redundant, curated database for reference (or type) nucleotide sequence records that supplies source data to numerous other databases. Building on recently proposed templates for filovirus variant naming [<virus name> (<strain>)/<isolation host-suffix>/<country of sampling>/<year of sampling>/<genetic variant designation>-<isolate designation>], we report consensus decisions from a majority of past and currently active filovirus experts on the eight filovirus type variants and isolates to be represented in RefSeq, their final designations, and their associated sequences.

Reversion of advanced Ebola virus disease in nonhuman primates with ZMapp

Without an approved vaccine or treatments, Ebola outbreak management has been limited to palliative care and barrier methods to prevent transmission. These approaches, however, have yet to end the 2014 outbreak of Ebola after its prolonged presence in West Africa. Here we show that a combination of monoclonal antibodies (ZMapp), optimized from two previous antibody cocktails, is able to rescue 100% of rhesus macaques when treatment is initiated up to 5 days post-challenge. High fever, viraemia and abnormalities in blood count and blood chemistry were evident in many animals before ZMapp intervention. Advanced disease, as indicated by elevated liver enzymes, mucosal haemorrhages and generalized petechia could be reversed, leading to full recovery. ELISA and neutralizing antibody assays indicate that ZMapp is cross-reactive with the Guinean variant of Ebola. ZMapp exceeds the efficacy of any other therapeutics described so far, and results warrant further development of this cocktail for clinical use.

Therapeutic intervention of Ebola virus infection in rhesus macaques with the MB-003 monoclonal antibody cocktail

Ebola virus (EBOV) remains one of the most lethal transmissible infections and is responsible for high fatality rates and substantial morbidity during sporadic outbreaks. With increasing human incursions into endemic regions and the reported possibility of airborne transmission, EBOV is a high-priority public health threat for which no preventive or therapeutic options are currently available. Recent studies have demonstrated that cocktails of monoclonal antibodies are effective at preventing morbidity and mortality in nonhuman primates (NHPs) when administered as a post-exposure prophylactic within 1 or 2 days of challenge. To test whether one of these cocktails (MB-003) demonstrates efficacy as a therapeutic (after the onset of symptoms), we challenged NHPs with EBOV and initiated treatment upon confirmation of infection according to a diagnostic protocol for U.S. Food and Drug Administration Emergency Use Authorization and observation of a documented fever. Of the treated animals, 43% survived challenge, whereas both the controls and all historical controls with the same challenge stock succumbed to infection. These results represent successful therapy of EBOV infection in NHPs.

Enhanced potency of a fucose-free monoclonal antibody being developed as an Ebola virus immunoprotectant

No countermeasures currently exist for the prevention or treatment of the severe sequelae of Filovirus (such as Ebola virus; EBOV) infection. To overcome this limitation in our biodefense preparedness, we have designed monoclonal antibodies (mAbs) which could be used in humans as immunoprotectants for EBOV, starting with a murine mAb (13F6) that recognizes the heavily glycosylated mucin-like domain of the virion-attached glycoprotein (GP). Point mutations were introduced into the variable region of the murine mAb to remove predicted human T-cell epitopes, and the variable regions joined to human constant regions to generate a mAb (h-13F6) appropriate for development for human use. We have evaluated the efficacy of three variants of h-13F6 carrying different glycosylation patterns in a lethal mouse EBOV challenge model. The pattern of glycosylation of the various mAbs was found to correlate to level of protection, with aglycosylated h-13F6 providing the least potent efficacy (ED(50) = 33 μg). A version with typical heterogenous mammalian glycoforms (ED(50) = 11 μg) had similar potency to the original murine mAb. However, h-13F6 carrying complex N-glycosylation lacking core fucose exhibited superior potency (ED(50) = 3 μg). Binding studies using Fcγ receptors revealed enhanced binding of nonfucosylated h-13F6 to mouse and human FcγRIII. Together the results indicate the presence of Fc N-glycans enhances the protective efficacy of h-13F6, and that mAbs manufactured with uniform glycosylation and a higher potency glycoform offer promise as biodefense therapeutics.

Toxicity of the bacterial luciferase substrate, n-decyl aldehyde, to Saccharomyces cerevisiae and Caenorhabditis elegans

This study determined that the bacterial luciferase fusion gene (luxAB) was not a suitable in vivo gene reporter in the model eukaryotic organisms Saccharomyces cerevisiae and Caenorhabditis elegans. LuxAB expressing S. cerevisiae strains displayed distinctive rapid decays in luminescence upon addition of the bacterial luciferase substrate, n-decyl aldehyde, suggesting a toxic response. Growth studies and toxicity bioassays have subsequently confirmed, that the aldehyde substrate was toxic to both organisms at concentrations well tolerated by Escherichia coli. As the addition of aldehyde is an integral part of the bacterial luciferase activity assay, our results do not support the use of lux reporter genes for in vivo analyses in these model eukaryotic organisms.

Development and application of bioluminescent Caenorhabditis elegans as multicellular eukaryotic biosensors

We describe a novel approach to assess toxicity to the free-living nematode Caenorhabditis elegans that relies on the ability of firefly luciferase to report on endogenous ATP levels. We have constructed bioluminescent C. elegans with the luc gene under control of a constitutive promoter. Light reduction was observed in response to increasing temperature, concentrations of copper, lead and 3,5-dichlorophenol. This was due to increased mortality coupled with decreased metabolic activity in the surviving animals. The light emitted by the transgenic nematodes gave a rapid, real-time indication of metabolic status. This forms the basis of rapid and biologically relevant toxicity tests.

Cadherin superfamily proteins in Caenorhabditis elegans and Drosophila melanogaster

The ability to form selective cell-cell adhesions is an essential property of metazoan cells. Members of the cadherin superfamily are important regulators of this process in both vertebrates and invertebrates. With the advent of genome sequencing projects, determination of the full repertoire of cadherins available to an organism is possible and here we present the identification and analysis of the cadherin repertoires in the genomes of Caenorhabditis elegans and Drosophila melanogaster. Hidden Markov models of cadherin domains were matched to the protein sequences obtained from the translation of the predicted gene sequences. Matches were made to 21 C. elegans and 18 D. melanogaster sequences. Experimental and theoretical work on C. elegans sequences, and data from ESTs, show that three pairs of genes, and two triplets, should be merged to form five single genes. It also produced sequence changes at one or both of the 5' and 3' termini of half the sequences. In D. melanogaster it is probable that two of the cadherin genes should also be merged together and that three cadherin genes should be merged with other neighbouring genes. Of the 15 cadherin proteins found in C. elegans, 13 have the features of cell surface proteins, signal sequences and transmembrane helices; the other two have only signal sequences. Of the 17 in D. melanogaster, 11 at present have both features and another five have transmembrane helices. The evidence currently available suggests about one-third of the cadherins in the two organisms can be grouped into subfamilies in which all, or parts of, the molecules are conserved. Each organism also has a approximately 980 residue protein (CDH-11 and CG11059) with two cadherin domains and whose sequences match well over their entire length two proteins from human brain. Two proteins in C. elegans, HMR-1A and HMR-1B, and three in D. melanogaster, CadN, Shg and CG7527, have cytoplasmic domains homologous to those of the classical cadherin genes of chordates but their extracellular regions have different domain structures. Other common subclasses include the seven-helix membrane cadherins, Fat-like protocadherins and the Ret-like cadherins. At present, the remaining cadherins have no obvious similarities in their extracellular domain architecture or homologies to their cytoplasmic domains and may, therefore, represent species-specific or phylum-specific molecules.

cdh-3, a gene encoding a member of the cadherin superfamily, functions in epithelial cell morphogenesis in Caenorhabditis elegans

Several genes that encode members of the cadherin superfamily have been identified in Caenorhabditis elegans. Based on the roles of cadherins in vertebrates and Drosophila, it is expected that they function in the control of epithelial morphogenesis, an event which is poorly understood at the molecular level in C. elegans. Reporter genes under the control of upstream sequences from one of these genes, cdh-3, are expressed in developing epithelial cells, but also in a number of neuroectodermal cells that extend processes along some of these epithelial cells. We generated a loss-of-function mutation in cdh-3 by transposon-mediated deletion mutagenesis. This mutation affects the morphogenesis of a single cell, hyp10, which forms the tip of the nematode tail. The lack of detectable defects associated with the other cells expressing cdh-3 reporter constructs hints at the existence of other genes that can compensate for cdh-3 loss of function.

Repression of gene expression in the embryonic germ lineage of C. elegans

The distinction between soma and germline was recognized more than a century ago: somatic cells form the body of an organism, whereas germ cells serve to produce future generations. In Caenorhabditis elegans, the separation of some and germline occurs through a series of asymmetrical divisions, in which embryonic germline blastomeres divide unequally to produce one somatic daughter and one germline daughter. Here we show that after each asymmetrical division, embryonically transcribed RNAs are detected in somatic, but not germline, blastomeres. This asymmetry depends on the activity of the germline specific factor, PIE-1. In the absence of PIE-1, embryonically transcribed RNAs are detected in both somatic and germline blastomeres. Furthermore, ectopic expression of PIE-1 in somatic blastomeres can significantly reduce the accumulation of new transcripts in these cells. Taken together, these results suggest that germ-cell fate depends on an inhibitory mechanism that blocks new gene expression in the early embryonic germ lineage.

Developmentally regulated alternative splicing of a nematode type IV collagen gene

A comparison of the genomic DNA sequence that encodes the Ascaris suum alpha 2(IV) collagen chain with the corresponding cDNA sequence led to the identification of a putative exon that was not expressed in the cDNA. The identification of this putative exon raised the possibility that transcripts of the alpha 2(IV) gene may undergo alternative splicing. We have used a reverse transcriptase-polymerase chain reaction assay to establish that such alternative splicing does indeed occur. Our results show that the A. suum alpha 2(IV) collagen gene produces at least two similar, but not identical, transcripts via the selection of two alternative exons. Furthermore, this alternative splicing appears to be developmentally regulated, suggesting that alternative splicing may be used in order to modify the properties of type IV collagen during nematode development.

The pogo transposable element family of Drosophila melanogaster

A 190 bp insertion is associated with the white-eosin mutation in Drosophila melanogaster. This insertion is a member of a family of transposable elements, pogo elements, which is of the same class as the P and hobo elements of D. melanogaster. Strains typically have many copies of a 190 bp element, 10-15 elements 1.1-1.5 kb in size and several copies of a 2.1 kb element. The smaller elements all appear to be derived from the largest by single internal deletions so that all elements share terminal sequences. They either always insert at the dinucleotide TA and have perfect 21 bp terminal inverse repeats, or have 22 bp inverse repeats and produce no duplication upon insertion. Analysis by DNA blotting of their distribution and occupancy of insertion sites in different strains suggests that they may be less mobile than P or hobo. The DNA sequence of the largest element has two long open reading frames on one strand which are joined by splicing as indicated by cDNA analysis. RNAs of this strand are made, whose sizes are similar to the major size classes of elements. A protein predicted by the DNA sequence has significant homology with a human centrosomal-associated protein, CENP-B. Homologous sequences were not detected in other Drosophila species, suggesting that this transposable element family may be restricted to D. melanogaster.

The complete primary structure of a nematode alpha 2(IV) collagen and the partial structural organization of its gene

We have isolated and characterized cDNA and genomic DNA clones which encode an alpha 2(IV) collagen chain from the parasitic nematode Ascaris suum. In addition we have determined, by nucleic acid sequence analysis, the structural organization of approximately two-thirds of the gene. This analysis has shown that the gene contains at least 15 introns, and those that have been characterized range in size from 141 to 854 base pairs. The derived protein sequence contains 1763 amino acids and includes a putative 26-amino acid signal sequence. The collagenous triple-helical region contains 17 interruptions, many of which occur in the same positions as those in the human alpha 1(IV) and alpha 2(IV) chains. Comparison of the genomic DNA sequence with the cDNA sequence has revealed the presence of a sequence within the gene which appears to be an intact and normal exon that is not represented in our cDNA sequence. The presence of this putative exon raises the possibility that the A. suum alpha 2(IV) collagen gene may undergo alternative splicing.

Structure and expression of Ascaris suum collagen genes: a comparison with Caenorhabditis elegans

We are interested in the structure and organization of collagen and collagen genes in the parasitic nematode Ascaris suum and in the control of collagen gene expression in Ascaris. In this nematode, as in all others studied, collagens constitute the major component of the extracellular cuticle and ultimately we would like to correlate the expression pattern of Ascaris cuticular collagen genes with the structure of the nematode cuticle. We would also like to see if there is any correlation between differential collagen gene expression and the biology and life-cycle of the parasite. In addition, we are also interested in comparing our data with the more extensive data available on collagen genes in the free living nematode Caenorhabditis elegans.