A Mutation in the Lettuce Infectious Yellows Virus Minor Coat Protein Disrupts Whitefly Transmission but Not In Planta Systemic Movement

The Lettuce infectious yellows virus (LIYV) RNA 2 mutant p1-5b was previously isolated from Bemisia tabaci-transmitted virus maintained in Chenopodium murale plants. p1-5b RNA 2 contains a single-nucleotide deletion in the minor coat protein (CPm) open reading frame (ORF) that is predicted to result in a frameshift and premature termination of the protein. Using the recently developed agroinoculation system for LIYV, we tested RNA 2 containing the p1-5b CPm mutant genotype (agro-pR6-5b) in Nicotiana benthamiana plants. We showed that plant infection triggered by agro-pR6-5b spread systemically and resulted in the formation of virions similar to those produced in p1-5b-inoculated protoplasts. However, virions derived from these mutant CPm genotypes were not transmitted by whiteflies, even though virion concentrations were above the typical transmission thresholds. In contrast, and as demonstrated for the first time, an engineered restoration mutant (agro-pR6-5bM1) was capable of both systemic movement in plants and whitefly transmission. These results provide strong molecular evidence that the full-length LIYV-encoded CPm is dispensable for systemic plant movement but is required for whitefly transmission.Members of the genus Crinivirus are emerging plant viruses in many parts of the world. An important factor contributing to the increase in the incidence of these viruses is their association with and transmission by whitefly vectors that have increased in distribution in the last several decades. Lettuce infectious yellows virus (LIYV), the type member of the genus Crinivirus (family Closteroviridae), is specifically transmitted by the sweet potato whitefly, Bemisia tabaci biotype A, in a semipersistent, noncirculative manner (6). The virus is confined to phloem cells within infected plants and is not transmissible to plants by leaf rub inoculation. The bipartite single-stranded positive-sense LIYV genome components, consisting of RNA 1 (approximately 8.1 kb) and RNA 2 (approximately 7.2 kb), are separately encapsidated in flexuous filamentous particles that are characteristic of the family Closteroviridae (8, 11). These virions are comprised of four protein components: the major coat protein (CP), the minor coat protein (CPm), an Hsp70 homolog (Hsp70h), and a 59-kDa protein (P59). Like other viruses in the family Closteroviridae, LIYV has bipolar virions with a “body” composed mainly of the CP and a “head” that is formed by the assembly of CPm subunits (2, 4, 7, 22, 28). Hsp70h and P59 are detected in LIYV virions (22), but their locations have not been identified, as they are not readily detected by immunogold labeling and transmission electron microscopy (IGL-TEM). For two members of the family Closteroviridae, Citrus tristeza virus (CTV) and Beet yellows virus (BYV), the combination of Hsp70h, P61 (the homolog of LIYV P59 in CTV) or P64 (the homolog of LIYV P59 in BYV), and CPm encapsidates the 5′ end (∼630 to 650 nucleotides [nt]) of the RNA genome, demonstrating the complex interactions that exist among the capsid proteins and the genomic RNA (15, 21).In our previous studies, we demonstrated the transmission of LIYV using an in vitro acquisition and whitefly transmission system (13, 22). Results from previous work implicated a role for LIYV CPm in whitefly transmission. Antibodies to CPm blocked the in vitro acquisition/transmission of LIYV virion preparations by B. tabaci biotype A, while antibodies to CP, Hsp70h, and P59 did not (22). The in vitro whitefly membrane-feeding system had also been used to demonstrate B. tabaci biotype A transmission of virions that were derived from cloned infectious cDNAs of LIYV RNA 1 and RNA 2 of several genotypes, including pR6 (the first cloned wild-type [WT] infectious cDNA of LIYV RNA 2 [10]), establishing for the first time that these cloned constructs contained all of the information necessary for protoplast infection, virion formation, whitefly transmission, and infection in plants (12). In that study, the mutant p1-5b was among the cloned LIYV RNA 2 cDNAs derived from B. tabaci biotype A-transmitted virus maintained in Chenopodium murale plants.p1-5b contains a single-adenine-residue deletion in the CPm open reading frame (ORF) at nucleotide 592, a deletion that is predicted to result in a frameshift, 14 new amino acids, and premature termination of the protein (12). The predicted p1-5b CPm has 211 amino acids, compared to 453 amino acids in the wild-type (pR6 genotype) protein. The p1-5b genotype also contains three other nucleotide changes in the CPm ORF relative to the pR6 infectious clone sequence (27), all of which result in amino acid changes. In contrast, the p1-5b CP, Hsp70h, and P59 sequences are identical to that of pR6 (12). Possible polymorphisms throughout the rest of the p1-5b clone were not characterized. In a prior study, B. tabaci biotype A transmission of p1-5b virions was not observed, even though the mutation did not affect its infectivity in protoplasts (as determined by virion yields) and apparent particle morphology (12). However, those studies were disadvantaged by the necessity of propagation in protoplasts to obtain specific genotypes from infectious cloned cDNAs. Protoplasts yield low quantities of virion relative to plants, and virion concentration is a critical parameter in whitefly transmission (13). Although virion concentrations in those experiments were above typical thresholds for whitefly transmission (12, 13), low concentrations may still be limiting for transmission, making negative transmission results difficult to interpret. Obtaining adequate virion concentrations of specific genotypes for whitefly transmission to plants has therefore been a significant hurdle to LIYV transmission studies.The recently developed agroinoculation method for LIYV (24) permits the study of systemic plant infection by distinct LIYV genotypes, including those that are whitefly transmission deficient, and the recovery of higher virion yields than were possible using protoplasts. The objective of this study was to further examine the function of the LIVY CPm by extending our observations of p1-5b. We constructed mutants with the CPm frameshift restored to determine if engineered mutations that either restored or disrupted the formation of an intact CPm also affected systemic plant infection, virion formation, and B. tabaci biotype A transmission. Our study revealed that a mutant engineered with the restored CPm ORF produced a WT infection profile characterized by systemic virus movement within agroinoculated plants and the generation of CPm-containing virions that were whitefly transmissible. Intriguingly, systemic virus movement was also observed for a mutant engineered to express the 1-5b CPm, but the virions lacked an identifiable CPm and were defective in whitefly transmission. These results represent a significant advance in addressing challenging questions and hypotheses about Crinivirus whitefly transmission properties not testable using earlier systems.     

Population Status of the Critically Endangered Preuss’s Red Colobus Monkey (Piliocolobus preussi Matschie 1900) and Recommendations for Its Conservation

International Journal of Primatology - Overhunting and habitat loss from the expansion of agriculture and extractive industries are the primary threats to primate species, 65% of which are...     

The MRN complex promotes DNA repair by homologous recombination and restrains antigenic variation in African trypanosomes

Homologous recombination dominates as the major form of DNA repair in Trypanosoma brucei, and is especially important for recombination of the subtelomeric variant surface glycoprotein during antigenic variation. RAD50, a component of the MRN complex (MRE11, RAD50, NBS1), is central to homologous recombination through facilitating resection and governing the DNA damage response. The function of RAD50 in trypanosomes is untested. Here we report that RAD50 and MRE11 are required for RAD51-dependent homologous recombination and phosphorylation of histone H2A following a DNA double strand break (DSB), but neither MRE11 nor RAD50 substantially influence DSB resection at a chromosome-internal locus. In addition, we reveal intrinsic separation-of-function between T. brucei RAD50 and MRE11, with only RAD50 suppressing DSB repair using donors with short stretches of homology at a subtelomeric locus, and only MRE11 directing DSB resection at the same locus. Finally, we show that loss of either MRE11 or RAD50 causes a greater diversity of expressed VSG variants following DSB repair. We conclude that MRN promotes stringent homologous recombination at subtelomeric loci and restrains antigenic variation.     

Discovery of Novel Herpes Simplexviruses in Wild Gorillas,Bonobos, and Chimpanzees Supports Zoonotic Origin of HSV-2

Viruses closely related to human pathogens can reveal the origins of human infectious diseases. Human herpes simplexvirus type 1 (HSV-1) and type 2 (HSV-2) are hypothesized to have arisen via host-virus codivergence and cross-species transmission. We report the discovery of novel herpes simplexviruses during a large-scale screening of fecal samples from wild gorillas, bonobos, and chimpanzees. Phylogenetic analysis indicates that, contrary to expectation, simplexviruses from these African apes are all more closely related to HSV-2 than to HSV-1. Molecular clock-based hypothesis testing suggests the divergence between HSV-1 and the African great ape simplexviruses likely represents a codivergence event between humans and gorillas. The simplexviruses infecting African great apes subsequently experienced multiple cross-species transmission events over the past 3 My, the most recent of which occurred between humans and bonobos around 1 Ma. These findings revise our understanding of the origins of human herpes simplexviruses and suggest that HSV-2 is one of the earliest zoonotic pathogens.     

Microscopic-Observation Drug-Susceptibility Assay for the Diagnosis of Drug-Resistant Tuberculosis in Harare,Zimbabwe

Introduction

Limited data exist on use of the microscopic-observation drug-susceptibility (MODS) assay among persons suspected of MDR-TB living in high HIV-prevalence settings.

Methods

We retrospectively reviewed available clinical and drug susceptibility data for drug-resistant TB suspects referred for culture and drug-susceptibility testing between April 1, 2011 and March 1, 2012. The diagnostic accuracy of MODS was estimated against a reference standard including Löwenstein-Jensen (LJ) media and manual liquid (BACTEC MGIT) culture. The accuracy of MODS drug-susceptibility testing (DST) was assessed against a reference standard absolute concentration method.

Results

One hundred thirty-eight sputum samples were collected from 99 drug-resistant TB suspects; in addition, six previously cultured MDR isolates were included for assessment of DST accuracy. Among persons with known HIV infection status, 39/59 (66%) were HIV-infected. Eighty-six percent of patients had a history of prior TB treatment, and 80% of individuals were on antituberculous treatment at the time of sample collection. M. tuberculosis was identified by reference standard culture among 34/98 (35%) MDR-TB suspects. Overall MODS sensitivity for M. tuberculosis detection was 85% (95% CI, 69–95%) and specificity was 93% (95% CI, 84–98%); diagnostic accuracy did not significantly differ by HIV infection status. Median time to positivity was significantly shorter for MODS (7 days; IQR 7–15 days) than MGIT (12 days; IQR 6–16 days) or LJ (28 days; IQR 21–35 days; p<0.001). Of 33 specimens with concurrent DST results, sensitivity of the MODS assay for detection of resistance to isoniazid, rifampin, and MDR-TB was 88% (95% CI, 68–97%), 96% (95% CI, 79–100%), and 91% (95% CI, 72–99%), respectively; specificity was 89% (95% CI, 52–100%), 89% (95% CI, 52–100%), and 90% (95% CI, 56–100%), respectively.

Conclusion

In a high HIV-prevalence setting, MODS diagnosed TB and drug-resistant TB with high sensitivity and shorter turnaround time compared with standard culture and DST methods.     

Choroid Sprouting Assay: An Ex Vivo Model of Microvascular Angiogenesis

Angiogenesis of the microvasculature is central to the etiology of many diseases including proliferative retinopathy, age-related macular degeneration and cancer. A mouse model of microvascular angiogenesis would be very valuable and enable access to a wide range of genetically manipulated tissues that closely approximate small blood vessel growth in vivo. Vascular endothelial cells cultured in vitro are widely used, however, isolating pure vascular murine endothelial cells is technically challenging. A microvascular mouse explant model that is robust, quantitative and can be reproduced without difficulty would overcome these limitations. Here we characterized and optimized for reproducibility an organotypic microvascular angiogenesis mouse and rat model from the choroid, a microvascular bed in the posterior of eye. The choroidal tissues from C57BL/6J and 129S6/SvEvTac mice and Sprague Dawley rats were isolated and incubated in Matrigel. Vascular sprouting was comparable between choroid samples obtained from different animals of the same genetic background. The sprouting area, normalized to controls, was highly reproducible between independent experiments. We developed a semi-automated macro in ImageJ software to allow for more efficient quantification of sprouting area. Isolated choroid explants responded to manipulation of the external environment while maintaining the local interactions of endothelial cells with neighboring cells, including pericytes and macrophages as evidenced by immunohistochemistry and fluorescence-activated cell sorting (FACS) analysis. This reproducible ex vivo angiogenesis assay can be used to evaluate angiogenic potential of pharmacologic compounds on microvessels and can take advantage of genetically manipulated mouse tissue for microvascular disease research.     

Oral Exposure to Phytomonas serpens Attenuates Thrombocytopenia and Leukopenia during Acute Infection with Trypanosoma cruzi

Mice infected with Trypanosoma cruzi, the agent of Chagas disease, rapidly develop anemia and thrombocytopenia. These effects are partially promoted by the parasite trans-sialidase (TS), which is shed in the blood and depletes sialic acid from the platelets, inducing accelerated platelet clearance and causing thrombocytopenia during the acute phase of disease. Here, we demonstrate that oral immunization of C57BL/6 mice with Phytomonas serpens, a phytoflagellate parasite that shares common antigens with T. cruzi but has no TS activity, reduces parasite burden and prevents thrombocytopenia and leukopenia. Immunization also reduces platelet loss after intraperitoneal injection of TS. In addition, passive transfer of immune sera raised in mice against P. serpens prevented platelet clearance. Thus, oral exposure to P. serpens attenuates the progression of thrombocytopenia induced by TS from T. cruzi. These findings are not only important for the understanding of the pathogenesis of T. cruzi infection but also for developing novel approaches of intervention in Chagas disease.     

Heterogeneity in Neutrophil Microparticles Reveals Distinct Proteome and Functional Properties

Altered plasma neutrophil microparticle levels have recently been implicated in a number of vascular and inflammatory diseases, yet our understanding of their actions is very limited. Herein, we investigate the proteome of neutrophil microparticles in order to shed light on their biological actions. Stimulation of human neutrophils, either in suspension or adherent to an endothelial monolayer, led to the production of microparticles containing >400 distinct proteins with only 223 being shared by the two subsets. For instance, postadherent microparticles were enriched in alpha-2 macroglobulin and ceruloplasmin, whereas microparticles produced by neutrophils in suspension were abundant in heat shock 70 kDa protein 1. Annexin A1 and lactotransferrin were expressed in both microparticle subsets. We next determined relative abundance of these proteins in three types of human microparticle samples: healthy volunteer plasma, plasma of septic patients and skin blister exudates finding that these proteins were differentially expressed on neutrophil microparticles from these samples reflecting in part the expression profiles we found in vitro. Functional assessment of the neutrophil microparticles subsets demonstrated that in response to direct stimulation neutrophil microparticles produced reactive oxygen species and leukotriene B₄ as well as locomoted toward a chemotactic gradient. Finally, we investigated the actions of the two neutrophil microparticles subsets described herein on target cell responses. Microarray analysis with human primary endothelial cells incubated with either microparticle subset revealed a discrete modulation of endothelial cell gene expression profile. These findings demonstrate that neutrophil microparticles are heterogenous and can deliver packaged information propagating the activation status of the parent cell, potentially exerting novel and fundamental roles both under homeostatic and disease conditions.The emerging notion that cells can communicate by packaged information represents a major shift in our understanding of cell-to-cell interaction in complex settings including inflammation (1). Packaging of mediators (irrespective of their chemical nature) in structures that can be transported through the vascular and lymphatic systems might avoid their rapid dilution and removal by biological fluids and allow the target cell or tissue to receive a biologically relevant amount of a given molecule. As an example, TNF-α produced by mast cells in the mouse paw can reach the lymph nodes unmodified, wrapped up in small structures or vesicles (2). In this respect, the last few years have witnessed augmented understanding in microparticle function.Described over 50 years ago (reviewed in (3, 4), microparticles are heterogeneous in nature with their size varying between 0.2 and 1.0 μm, and are characterized by an outer membrane composed of a phospholipid bilayer and cell surface proteins. The mechanism of microparticle production is not fully understood, though it may follow processes not dissimilar from those observed in apoptosis, involving membrane detachment from the anchoring cytoskeleton and loss of membrane symmetry, which leads to exposure of negatively charged phospholipids (5–7). Proteins found on the outer leaflet of the microparticle cell membrane are believed to reflect both the origin and activation status of the parental cell (8, 9); for instance, microparticles from neutrophils express CD66b and CD62L (10, 11). We have recently identified the selective expression of the potent anti-inflammatory and proresolving protein Annexin A1 (ANXA1) on the surface of microparticles generated from neutrophils adherent to endothelial monolayers, when compared with those prepared from quiescent neutrophils (12). Microparticle production is not restricted to one subset of cells and using cell specific antigens the relative contribution of different cell types to the total microparticle population in a particular environment can be assessed. This has allowed for the analysis of different microparticle populations (the focus being by and large platelet- and endothelial-derived microparticles) in a number of pathologies in the quest to identify robust biomarkers for disease and treatment (13–15). With regard to inflammatory diseases, examples would include plasma samples in sepsis (16), psoriatic arthritis (17), and scleroderma (18). However, the vast majority of these studies have only determined microparticle expression patterns with respect to the cell type of origin, without addressing the possibility that microparticle composition—even when generated from the same leukocyte subset—might differ in relation to disease status and/or mode of cell activation. Of note recent work has also demonstrated that the production of neutrophil microparticles during self-limited inflammation is temporally regulated suggesting that these microparticles are important in orchestrating inflammation-resolution (1).Recent work has established that microparticles can elicit a variety of biological processes ranging from angiogenesis to anti-inflammation; so that it is very unlikely they can continue to be considered “cell debris,” as initially postulated. The following are some examples, relevant to the present study. Ingestion of platelet microparticles alters the phenotype of macrophages, leading to the false identification of endothelial cell progenitor cells in culture (19). Likewise, sonic hedgehog can be transferred, via microparticles, to dysfunctional endothelial cells, restoring the activity of nitric oxide synthase with downstream production of nitric oxide (20). Microparticles can carry functionally active receptor proteins to target cells (21, 22). Finally, in vivo generation of microparticles has been observed within the inflamed microcirculation. Real time analysis of leukocyte recruitment has visualized microparticle release from leukocytes squeezing through an endothelial barrier, providing evidence for their formation in vivo together with potential functional relevance in relation to cell migration (23).On stimulation, neutrophils produce microparticles with rapid and nongenomic anti-inflammatory properties, in vitro and in vivo, reliant on their expression of ANXA1 (12). Whereas these findings are consistent with those obtained by Gasser and colleagues (24) who described inhibitory properties of neutrophil microparticles, other studies have suggested that the same cell type can produce microparticles that elicit activating properties, for instance upon incubation with endothelial cells or monocytes for longer time-points (25, 26). Thus, to gain further insight into the potential mechanisms involved in mediating such distinct effects, we deemed it important to determine the total proteome of neutrophil microparticles. Having established that different stimulation conditions yield microparticle populations with distinct protein profiles, we corroborated our observations in two distinct clinical scenarios, characterizing neutrophil microparticles from skin blister exudates and plasma samples from sepsis patients using a select group of proteins identified in our proteomic profile. We also established that the two microparticles subsets differentially modulate endothelial cell gene expression profile and thereby function, as determined by connectivity map analysis.     

The effects of staged intra-articular injection of cultured autologous mesenchymal stromal cells on the repair of damaged cartilage: a pilot study in caprine model

Introduction

Treatment of chondral injuries remains a major issue despite the many advances made in cartilage repair techniques. Although it has been postulated that the use of marrow stimulation in combination with cell-based therapy may provide superior outcome, this has yet to be demonstrated. A pilot study was thus conducted to determine if bone marrow derived mesenchymal stromal cells (BM-MSCs) have modulatory effects on the repair outcomes of bone marrow stimulation (BMS) techniques.

Methods

Two full-thickness chondral 5 mm diameter defects were created in tandem on the medial condyle of left stifle joints of 18 Boer caprine (N = 18). Goats were then divided equally into three groups. Simultaneously, bone marrow aspirates were taken from the iliac crests from the goats in Group 1 and were sent for BM-MSC isolation and expansion in vitro. Six weeks later, BMS surgery, which involves subchondral drilling at the defect sites, was performed. After two weeks, the knees in Group 1 were given autologous intra-articular BM-MSCs (N = 6). In Group 2, although BMS was performed there were no supplementations provided. In Group 3, no intervention was administered. The caprines were sacrificed after six months. Repairs were evaluated using macroscopic assessment through the International Cartilage Repair Society (ICRS) scoring, histologic grading by O’Driscoll score, biochemical assays for glycosaminoglycans (GAGs) and gene expressions for aggrecan, collagen II and Sox9.

Results

Histological and immunohistochemical analyses demonstrated hyaline-like cartilage regeneration in the transplanted sites particularly in Group 1. In contrast, tissues in Groups 2 and 3 demonstrated mainly fibrocartilage. The highest ICRS and O’Driscoll scorings was also observed in Group 1, while the lowest score was seen in Group 3. Similarly, the total GAG/total protein as well as chondrogenic gene levels were expressed in the same order, that is highest in Group 1 while the lowest in Group three. Significant differences between these 3 groups were observed (P <0.05).

Conclusions

This study suggests that supplementing intra-articular injections of BM-MSCs following BMS knee surgery provides superior cartilage repair outcomes.