From frog integument to human skin: dermatological perspectives from frog skin biology

For over a century, frogs have been studied across various scientific fields, including physiology, embryology, neuroscience, (neuro)endocrinology, ecology, genetics, behavioural science, evolution, drug development, and conservation biology. In some cases, frog skin has proven very successful as a research model, for example aiding in the study of ion transport through tight epithelia, where it has served as a model for the vertebrate distal renal tubule and mammalian epithelia. However, it has rarely been considered in comparative studies involving human skin. Yet, despite certain notable adaptations that have enabled frogs to survive in both aquatic and terrestrial environments, frog skin has many features in common with human skin. Here we present a comprehensive overview of frog (and toad) skin ontogeny, anatomy, cytology, neuroendocrinology and immunology, with special attention to its unique adaptations as well as to its similarities with the mammalian integument, including human skin. We hope to provide a valuable reference point and a source of inspiration for both amphibian investigators and mammalian researchers studying the structural and functional properties of the largest organ of the vertebrate body.     

High-Throughput Chemical Screening for Antivirulence Developmental Phenotypes in Trypanosoma brucei

In the bloodstream of mammalian hosts, the sleeping sickness parasite, Trypanosoma brucei, exists as a proliferative slender form or a nonproliferative, transmissible, stumpy form. The transition between these developmental forms is controlled by a density-dependent mechanism that is important for the parasite''s infection dynamics, immune evasion via ordered antigenic variation, and disease transmissibility. However, stumpy formation has been lost in most laboratory-adapted trypanosome lines, generating monomorphic parasites that proliferate uncontrolled as slender forms in vitro and in vivo. Nonetheless, these forms are readily amenable to cell culture and high-throughput screening for trypanocidal lead compounds. Here, we have developed and exploited a high-throughput screen for developmental phenotypes using a transgenic monomorphic cell line expressing a reporter under the regulation of gene control signals from the stumpy-specific molecule PAD1. Using a whole-cell fluorescence-based assay to screen over 6,000 small molecules from a kinase-focused compound library, small molecules able to activate stumpy-specific gene expression and proliferation arrest were assayed in a rapid assay format. Independent follow-up validation identified one hit able to induce modest, yet specific, changes in mRNA expression indicative of a partial differentiation to stumpy forms in monomorphs. Further, in pleomorphs this compound induced a stumpy-like phenotype, entailing growth arrest, morphological changes, PAD1 expression, and enhanced differentiation to procyclic forms. This not only provides a potential tool compound for the further understanding of stumpy formation but also demonstrates the use of high-throughput screening in the identification of compounds able to induce specific phenotypes, such as differentiation, in African trypanosomes.     

A large genomic island allows Neisseria meningitidis to utilize propionic acid,with implications for colonization of the human nasopharynx

Neisseria meningitidis is an important human pathogen that is capable of killing within hours of infection. Its normal habitat is the nasopharynx of adult humans. Here we identify a genomic island (the prp gene cluster) in N. meningitidis that enables this species to utilize propionic acid as a supplementary carbon source during growth, particularly under nutrient poor growth conditions. The prp gene cluster encodes enzymes for a methylcitrate cycle. Novel aspects of the methylcitrate cycle in N. meningitidis include a propionate kinase which was purified and characterized, and a putative propionate transporter. This genomic island is absent from the close relative of N. meningitidis, the commensal Neisseria lactamica, which chiefly colonizes infants not adults. We reason that the possession of the prp genes provides a metabolic advantage to N. meningitidis in the adult oral cavity, which is rich in propionic acid‐generating bacteria. Data from classical microbiological and sequence‐based microbiome studies provide several lines of supporting evidence that N. meningitidis colonization is correlated with propionic acid generating bacteria, with a strong correlation between prp‐containing Neisseria and propionic acid generating bacteria from the genus Porphyromonas, and that this may explain adolescent/adult colonization by N. meningitidis.     

A promising biological control agent for the invasive alien plant,Pereskia aculeata Miller (Cactaceae), in South Africa

Pereskia aculeata Miller (Cactaceae) is an invasive alien plant from Central and South America that has become a problematic environmental weed in South Africa. A potential biological control agent, the stem-wilter, Catorhintha schaffneri Brailovsky & Garcia (Coreidae), was collected in southern Brazil and imported into quarantine in South Africa. Field host range data suggested that C. schaffneri has a host range restricted to P. aculeata. No-choice nymph survival tests were then conducted on 27 test plant species in 9 families. Survival to the adult stage was only recorded on P. aculeata and the closely related Pereskia grandifolia Haw. (Cactaceae). Mortality was significantly higher on P. grandifolia with only 3% of the nymphs reaching the adult stage compared with 74% on P. aculeata indicating that P. aculeata is the primary host plant. P. grandifolia is native in South America and is of no agricultural importance in South Africa so any feeding on P. grandifolia in South Africa would have no negative environmental or economic consequences. In other tests, adult survival on P. aculeata [25.8 days (SE ± 3.74)] was significantly longer than on other test plant species [4.3 days (SE ± 0.36)] further confirming the host specificity of the species. Impact studies conducted in quarantine indicated that C. schaffneri is damaging to P. aculeata, significantly reducing the number of leaves and the shoot lengths of plants, even at relatively low insect densities. C. schaffneri is safe for release in South Africa and is likely to be a damaging and effective agent.     

Epitope detection chromatography: a method to dissect the structural heterogeneity and inter‐connections of plant cell‐wall matrix glycans

Plant cell walls are complex, multi‐macromolecular assemblies of glycans and other molecules and their compositions and molecular architectures vary extensively. Even though the chemistry of cell‐wall glycans is now well understood, it remains a challenge to understand the diversity of glycan configurations and interactions in muro, and how these relate to changes in the biological and mechanical properties of cell walls. Here we describe in detail a method called epitope detection chromatography analysis of cell‐wall matrix glycan sub‐populations and inter‐connections. The method combines chromatographic separations with use of glycan‐directed monoclonal antibodies as detection tools. The high discrimination capacity and high sensitivity for the detection of glycan structural features (epitopes) provided by use of established monoclonal antibodies allows the study of oligosaccharide motifs on sets of cell‐wall glycans in small amounts of plant materials such as a single organ of Arabidopsis thaliana without the need for extensive purification procedures. We describe the use of epitope detection chromatography to assess the heterogeneity of xyloglucan and pectic rhamnogalacturonan I sub‐populations and their modulation in A. thaliana organs.     

Accumulating Research: A Systematic Account of How Cumulative Meta-Analyses Would Have Provided Knowledge,Improved Health,Reduced Harm and Saved Resources

Background

“Cumulative meta-analysis” describes a statistical procedure to calculate, retrospectively, summary estimates from the results of similar trials every time the results of a further trial in the series had become available. In the early 1990s, comparisons of cumulative meta-analyses of treatments for myocardial infarction with advice promulgated through medical textbooks showed that research had continued long after robust estimates of treatment effects had accumulated, and that medical textbooks had overlooked strong, existing evidence from trials. Cumulative meta-analyses have subsequently been used to assess what could have been known had new studies been informed by systematic reviews of relevant existing evidence and how waste might have been reduced.

Methods and Findings

We used a systematic approach to identify and summarise the findings of cumulative meta-analyses of studies of the effects of clinical interventions, published from 1992 to 2012. Searches were done of PubMed, MEDLINE, EMBASE, the Cochrane Methodology Register and Science Citation Index. A total of 50 eligible reports were identified, including more than 1,500 cumulative meta-analyses. A variety of themes are illustrated with specific examples. The studies showed that initially positive results became null or negative in meta-analyses as more trials were done; that early null or negative results were over-turned; that stable results (beneficial, harmful and neutral) would have been seen had a meta-analysis been done before the new trial; and that additional trials had been much too small to resolve the remaining uncertainties.

Conclusions

This large, unique collection of cumulative meta-analyses highlights how a review of the existing evidence might have helped researchers, practitioners, patients and funders make more informed decisions and choices about new trials over decades of research. This would have led to earlier uptake of effective interventions in practice, less exposure of trial participants to less effective treatments, and reduced waste resulting from unjustified research.     

Plasticity of the ��-Trefoil Protein Fold in the Recognition and Control of Invertebrate Predators and Parasites by a Fungal Defence System

Discrimination between self and non-self is a prerequisite for any defence mechanism; in innate defence, this discrimination is often mediated by lectins recognizing non-self carbohydrate structures and so relies on an arsenal of host lectins with different specificities towards target organism carbohydrate structures. Recently, cytoplasmic lectins isolated from fungal fruiting bodies have been shown to play a role in the defence of multicellular fungi against predators and parasites. Here, we present a novel fruiting body lectin, CCL2, from the ink cap mushroom Coprinopsis cinerea. We demonstrate the toxicity of the lectin towards Caenorhabditis elegans and Drosophila melanogaster and present its NMR solution structure in complex with the trisaccharide, GlcNAcβ1,4[Fucα1,3]GlcNAc, to which it binds with high specificity and affinity in vitro. The structure reveals that the monomeric CCL2 adopts a β-trefoil fold and recognizes the trisaccharide by a single, topologically novel carbohydrate-binding site. Site-directed mutagenesis of CCL2 and identification of C. elegans mutants resistant to this lectin show that its nematotoxicity is mediated by binding to α1,3-fucosylated N-glycan core structures of nematode glycoproteins; feeding with fluorescently labeled CCL2 demonstrates that these target glycoproteins localize to the C. elegans intestine. Since the identified glycoepitope is characteristic for invertebrates but absent from fungi, our data show that the defence function of fruiting body lectins is based on the specific recognition of non-self carbohydrate structures. The trisaccharide specifically recognized by CCL2 is a key carbohydrate determinant of pollen and insect venom allergens implying this particular glycoepitope is targeted by both fungal defence and mammalian immune systems. In summary, our results demonstrate how the plasticity of a common protein fold can contribute to the recognition and control of antagonists by an innate defence mechanism, whereby the monovalency of the lectin for its ligand implies a novel mechanism of lectin-mediated toxicity.     

Rab25 and CLIC3 collaborate to promote integrin recycling from late endosomes/lysosomes and drive cancer progression

Here we show that Rab25 permits the sorting of ligand-occupied, active-conformation α5β1 integrin to late endosomes/lysosomes. Photoactivation and biochemical approaches show that lysosomally targeted integrins are not degraded but are retrogradely transported and recycled to the plasma membrane at the back of invading cells. This requires CLIC3, a protein upregulated in Rab25-expressing cells and tumors, which colocalizes with active α5β1 in late endosomes/lysosomes. CLIC3 is necessary for release of the cell rear during migration on 3D matrices and is required for invasion and maintenance of active Src signaling in organotypic microenvironments. CLIC3 expression predicts lymph node metastasis and poor prognosis in operable cases of pancreatic ductal adenocarcinoma (PDAC). The identification of CLIC3 as a regulator of a recycling pathway and as an independent prognostic indicator in PDAC highlights the importance of active integrin trafficking as a potential drive to cancer progression in vivo.