The Giardia ventrolateral flange is a lamellar membrane protrusion that supports attachment

Attachment to the intestinal epithelium is critical to the lifestyle of the ubiquitous parasite Giardia lamblia. The ventrolateral flange is a sheet-like membrane protrusion at the interface between parasites and attached surfaces. This structure has been implicated in attachment, but its role has been poorly defined. Here, we identified a novel actin associated protein with putative WH2-like actin binding domains we named Flangin. Flangin complexes with Giardia actin (GlActin) and is enriched in the ventrolateral flange making it a valuable marker for studying the flanges’ role in Giardia biology. Live imaging revealed that the flange grows to around 1 μm in width after cytokinesis, then remains uniform in size during interphase, grows in mitosis, and is resorbed during cytokinesis. A flangin truncation mutant stabilizes the flange and blocks cytokinesis, indicating that flange disassembly is necessary for rapid myosin-independent cytokinesis in Giardia. Rho family GTPases are important regulators of membrane protrusions and GlRac, the sole Rho family GTPase in Giardia, was localized to the flange. Knockdown of Flangin, GlActin, and GlRac result in flange formation defects. This indicates a conserved role for GlRac and GlActin in forming membrane protrusions, despite the absence of canonical actin binding proteins that link Rho GTPase signaling to lamellipodia formation. Flangin-depleted parasites had reduced surface contact and when challenged with fluid shear force in flow chambers they had a reduced ability to remain attached, confirming a role for the flange in attachment. This secondary attachment mechanism complements the microtubule based adhesive ventral disc, a feature that may be particularly important during mitosis when the parental ventral disc disassembles in preparation for cytokinesis. This work supports the emerging view that Giardia’s unconventional actin cytoskeleton has an important role in supporting parasite attachment.     

Pathological and immunological evaluation of different regimens of praziquantel treatment in a mouse model of Schistosoma mansoni infection

BackgroundOne of the considerable challenges of schistosomiasis chemotherapy is the inefficacy of praziquantel (PZQ) at the initial phase of the infection. Immature schistosomes are not susceptible to PZQ at the curative dose. Here, we investigated the efficacy of different PZQ regimens administered during the initial stage of Schistosoma mansoni infection in mice.Methodology/Principal findingsTwo months-old mice were individually infected with 80 S. mansoni cercariae and divided into one infected-untreated control group (IC) and four PZQ-treated groups: PZQ at 100 mg/kg/day for five consecutive days (group PZQ1), PZQ at 100 mg/kg/day for 28 days (group PZQ2), PZQ at 18 mg/kg/day for 28 days (group PZQ3) and a single dose of PZQ at 500 mg/kg (group PZQ4). The treatment started on day one post-infection (p.i), and each group of mice was divided into two subgroups euthanized on day 36 or 56 p.i, respectively. We determined the mortality rate, the parasitological burden, the hepatic and intestinal granulomas, the serum levels of Th-1, Th-2, and Th-17 cytokines, and gene expression. The treatment led to a significant (p < 0.001) reduction of worm burden and egg counts in the intestine and liver in groups PZQ2 and PZQ3. On 56^th day p.i, there was a significant reduction (p < 0.001) of the number and volume of the hepatic granulomas in groups PZQ2 and PZQ3 compared to group PZQ1 or PZQ4. Moreover, in group PZQ3, the serum levels of IFN-γ, TNF-α, IL-13, and IL-17 and their liver mRNA expressions were significantly reduced while IL-10 and TGF-β gene expression significantly increased. The highest mortality rate (81.25%) was recorded in group PZQ2.Conclusion/SignificanceThis study revealed that the administration of PZQ at 18 mg/kg/day for 28 consecutive days was the optimal effective posology for treating S. mansoni infection at the initial stage in a murine model.     

Transplacental Zika virus transmission in ex vivo perfused human placentas

A Zika virus (ZIKV) infection during pregnancy can result in severe birth defects such as microcephaly. To date, it is incompletely understood how ZIKV can cross the human placenta. Furthermore, results from studies in pregnant mice and non-human primates are conflicting regarding the role of cross-reactive dengue virus (DENV) antibodies on transplacental ZIKV transmission. Elucidating how ZIKV can cross the placenta and which risk factors contribute to this is important for risk assessment and for potential intervention strategies for transplacental ZIKV transmission. In this study we use an ex vivo human placental perfusion model to study transplacental ZIKV transmission and the effect that cross-reactive DENV antibodies have on this transmission. By using this model, we demonstrate that DENV antibodies significantly increase ZIKV uptake in perfused human placentas and that this increased uptake is neonatal Fc-receptor-dependent. Furthermore, we show that cross-reactive DENV antibodies enhance ZIKV infection in term human placental explants and in primary fetal macrophages but not in primary trophoblasts. Our data supports the hypothesis that presence of cross-reactive DENV antibodies could be an important risk factor for transplacental ZIKV transmission. Furthermore, we demonstrate that the ex vivo placental perfusion model is a relevant and animal friendly model to study transplacental pathogen transmission.     

Mismatch discrimination and sequence bias during end-joining by DNA ligases

DNA ligases, critical enzymes for in vivo genome maintenance and modern molecular biology, catalyze the joining of adjacent 3′-OH and 5′-phosphorylated ends in DNA. To determine whether DNA annealing equilibria or properties intrinsic to the DNA ligase enzyme impact end-joining ligation outcomes, we used a highly multiplexed, sequencing-based assay to profile mismatch discrimination and sequence bias for several ligases capable of efficient end-joining. Our data reveal a spectrum of fidelity and bias, influenced by both the strength of overhang annealing as well as sequence preferences and mismatch tolerances that vary both in degree and kind between ligases. For example, while T7 DNA ligase shows a strong preference for ligating high GC sequences, other ligases show little GC-dependent bias, with human DNA Ligase 3 showing almost none. Similarly, mismatch tolerance varies widely among ligases, and while all ligases tested were most permissive of G:T mismatches, some ligases also tolerated bulkier purine:purine mismatches. These comprehensive fidelity and bias profiles provide insight into the biology of end-joining reactions and highlight the importance of ligase choice in application design.     

A single domain of the replication termination protein of Bacillus subtilis is involved in arresting both DnaB helicase and RNA polymerase

The current models that have been proposed to explain the mechanism of replication termination are (i) passive arrest of a replication fork by the terminus (Ter) DNA-terminator protein complex that impedes the replication fork and the replicative helicase in a polar fashion and (ii) an active barrier model in which the Ter-terminator protein complex arrests a fork not only by DNA-protein interaction but also by mechanistically significant terminator protein-helicase interaction. Despite the existence of some evidence supporting in vitro interaction between the replication terminator protein (RTP) and DnaB helicase, there has been continuing debate in the literature questioning the validity of the protein-protein interaction model. The objective of the present work was two-fold: (i) to reexamine the question of RTP-DnaB interaction by additional techniques and different mutant forms of RTP, and (ii) to investigate if a common domain of RTP is involved in the arrest of both helicase and RNA polymerase. The results validate and confirm the RTP-DnaB interaction in vitro and suggest a critical role for this interaction in replication fork arrest. The results also show that the Tyr(33) residue of RTP plays a critical role both in the arrest of helicase and RNA polymerase.     

Mirrored Genome Size Distributions in Monocot and Dicot Plants

The variation in genome size and basic chromosome number was analyzed in the wide range of angiosperm plants. A divergence of monocots vs. dicots (eudicots) genome size distributions was revealed. A similar divergence was found for annual vs. perennial dicots. The divergence of monocots vs. dicots genome size distributions holds at different taxonomic levels and is more pronounced for species with larger genomes. Using nested analysis of variance, it was shown that putative constraints on genome size variation are not only stronger in dicots as compared to monocots but in the former they start to operate already at the family level, whereas in the latter they do so only at the order level. At the same time, variation in basic chromosome number is constrained at the order level in both groups. Higher basic chromosome numbers were found in perennial plants as compared to the annual ones, which can be explained by their need for a higher genetic recombination as compensation for the longer life-cycles. A negative correlation was found between genome size and basic chromosome number, which can be explained as a trade-off between different recombination mechanisms.     

Peptide loading in the endoplasmic reticulum accelerates trafficking of peptide: MHC class II complexes in B cells

In a combination of biochemical and immunoelectron-microscopical approaches we studied intracellular trafficking and localization of the endoplasmic-reticulum (ER)-formed complexes of murine MHC class II molecule I-A^b and an antigenic peptide E52–68 covalently linked to its -chain. The association with the peptide in the ER leads to sharp acceleration of the intracellular trafficking of the complexes to the plasma membrane. Within the cells, E52–68:I-A^b complexes accumulate in the multivesicular MHC class II compartment (MIIC), but not in denser multilaminar or intermediate type MIICs. The changes in the trafficking of ER-formed complexes result solely from the presence of the tethered peptide, since wild-type class II molecules traffic similarly in bare lymphocyte syndrome cells and in wild-type antigen-presenting cells.