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It is widely believed that cleavage-furrow formation during cytokinesis is driven by the contraction of a ring containing F-actin and type-II myosin. However, even in cells that have such rings, they are not always essential for furrow formation. Moreover, many taxonomically diverse eukaryotic cells divide by furrowing but have no type-II myosin, making it unlikely that an actomyosin ring drives furrowing. To explore this issue further, we have used one such organism, the green alga Chlamydomonas reinhardtii. We found that although F-actin is associated with the furrow region, none of the three myosins (of types VIII and XI) is localized there. Moreover, when F-actin was eliminated through a combination of a mutation and a drug, furrows still formed and the cells divided, although somewhat less efficiently than normal. Unexpectedly, division of the large Chlamydomonas chloroplast was delayed in the cells lacking F-actin; as this organelle lies directly in the path of the cleavage furrow, this delay may explain, at least in part, the delay in cytokinesis itself. Earlier studies had shown an association of microtubules with the cleavage furrow, and we used a fluorescently tagged EB1 protein to show that microtubules are still associated with the furrows in the absence of F-actin, consistent with the possibility that the microtubules are important for furrow formation. We suggest that the actomyosin ring evolved as one way to improve the efficiency of a core process for furrow formation that was already present in ancestral eukaryotes.

Aims Current treatments of prosthetic joint infection (PJI) are minimally effective against Staphylococcus aureus biofilm. A murine PJI model of debridement, antibiotics, and implant retention (DAIR) was used to test the hypothesis that PlySs2, a bacteriophage-derived lysin, can target S. aureus biofilm and address the unique challenges presented in this periprosthetic environment. Methods The ability of PlySs2 and vancomycin to kill biofilm and colony-forming units (CFUs) on orthopaedic implants were compared using in vitro models. An in vivo murine PJI model of DAIR was used to assess the efficacy of a combination of PlySs2 and vancomycin on periprosthetic bacterial load. Results PlySs2 treatment reduced 99% more CFUs and 75% more biofilm compared with vancomycin in vitro. A combination of PlySs2 and vancomycin in vivo reduced the number of CFUs on the surface of implants by 92% and in the periprosthetic tissue by 88%. Conclusion PlySs2 lysin was able to reduce biofilm, target planktonic bacteria, and work synergistically with vancomycin in our in vitro models. A combination of PlySs2 and vancomycin also reduced bacterial load in periprosthetic tissue and on the surface of implants in a murine model of DAIR treatment for established PJI.

Genes encoding cell-surface proteins control nervous system development and are implicated in neurological disorders. These genes produce alternative mRNA isoforms which remain poorly characterized, impeding understanding of how disease-associated mutations cause pathology. Here we introduce a strategy to define complete portfolios of full-length isoforms encoded by individual genes. Applying this approach to neural cell-surface molecules, we identify thousands of unannotated isoforms expressed in retina and brain. By mass spectrometry we confirm expression of newly-discovered proteins on the cell surface in vivo. Remarkably, we discover that the major isoform of a retinal degeneration gene, CRB1, was previously overlooked. This CRB1 isoform is the only one expressed by photoreceptors, the affected cells in CRB1 disease. Using mouse mutants, we identify a function for this isoform at photoreceptor-glial junctions and demonstrate that loss of this isoform accelerates photoreceptor death. Therefore, our isoform identification strategy enables discovery of new gene functions relevant to disease. Here the authors present an approach that can reveal the full complement of mRNA isoforms encoded by individual genes, and they identify a major isoform of the retinal degeneration gene CRB1 which functions at the cell-cell junctions of the outer limiting membrane to promote photoreceptor survival.

Although much is known about the interaction of fibrinogen with alpha IIb beta 3, much less is known about the interaction of platelets with cross-linked fibrin. Fibrinogen residue Lys406 plays a vital role in the interaction of fibrinogen with alpha IIb beta 3, but because it participates in fibrin cross-linking, it is not available for interacting with alpha IIb beta 3. We studied the adhesion of platelets and HEK cells expressing normal and constitutively active alpha IIb beta 3 to both immobilized fibrinogen and D-dimer, a proteolytic fragment of cross-linked fibrin, as well as platelet-mediated clot retraction. Nonactivated platelets and HEK cells expressing normal alpha IIb beta 3 adhered to fibrinogen but not D-dimer, whereas activated platelets as well as HEK cells expressing activated alpha IIb beta 3 both bound to D-dimer. Small-molecule antagonists of the alpha IIb beta 3 RGD (Arg-Gly-Asp) binding pocket inhibited adhesion to D-dimer, and an Asp119Ala mutation that disrupts the beta 3 metal ion-dependent adhesion site inhibited alpha IIb beta 3-mediated adhesion to D-dimer. D-dimer and a polyclonal antibody against D-dimer inhibited clot retraction. The monoclonal antibody (mAb) 10E5, directed at alpha IIb and a potent inhibitor of platelet interactions with fibrinogen, did not inhibit the interaction of activated platelets with D-dimer or dot retraction, whereas the mAb 7E3, directed at beta 3, inhibited both phenomena. We conclude that activated, but not nonactivated, alpha IIb beta 3 mediates interactions between platelets and D-dimer, and by extrapolation, to cross-linked fibrin. Although the interaction of alpha IIb beta 3 with D-dimer differs from that with fibrinogen, it probably involves contributions from regions on beta 3 that are close to, or that are affected by, changes in the RGD binding pocket.

The foamy viruses (FV) or spumaviruses are an ancient subfamily of retroviruses that infect a variety of vertebrates. FVs are endemic, but apparently apathogenic, in modern non-human primates. Like other retroviruses, FV replication is inhibited by type-I interferon (IFN). In a previously described screen of IFN-stimulated genes (ISGs), we identified the macaque PHD finger domain protein-11 (PHF11) as an inhibitor of prototype foamy virus (PFV) replication. Here, we show that human and macaque PHF11 inhibit the replication of multiple spumaviruses, but are inactive against several orthoretroviruses. Analysis of other mammalian PHF11 proteins revealed that antiviral activity is host species dependent. Using multiple reporter viruses and cell lines, we determined that PHF11 specifically inhibits a step in the replication cycle that is unique to FVs, namely basal transcription from the FV internal promoter (IP). In so doing, PHF11 prevents expression of the viral transactivator Tas and subsequent activation of the viral LTR promoter. These studies reveal a previously unreported inhibitory mechanism in mammalian cells, that targets a family of ancient viruses and may promote viral latency. Author summary Foamy viruses have a unique replication strategy and long evolutionary relationship with their vertebrate hosts that has resulted in wide-spread infection of modern species without any apparent pathogenic consequence. How foamy virus infections are controlled by their hosts is unknown. Here, we demonstrate that infection of a variety of foamy viruses is inhibited by the interferon-stimulated gene product, PHF11, in a species-dependent manner. We show that PHF11 prevents replication by a previously undescribed mechanism, namely by inhibiting gene expression from an internal viral promoter, a conserved and distinct feature of the foamy viruses. Inhibition of early viral gene expression by PHF11 may promote viral latency and the apathogenicity of foamy viruses.

Base excision repair (BER) maintains genomic stability through the repair of DNA damage. Within BER, AP-endonuclease 1 (APE1) is a multifunctional enzyme that processes DNA intermediates through its backbone cleavage activity. To accomplish these repair activities, APE1 must recognize and accommodate several diverse DNA substrates. This is hypothesized to occur through a DNA sculpting mechanism where structural adjustments of the DNA substrate are imposed by the protein; however, how APE1 uniquely sculpts each substrate within a single rigid active site remains unclear. Here, we utilize structural and biochemical approaches to probe the DNA sculpting mechanism of APE1, specifically by characterizing a protein loop that intercalates the minor groove of the DNA (termed the intercalating loop). Pre-steady-state kinetics reveal a tyrosine residue within the intercalating loop (Y269) that is critical for AP-endonuclease activity. Using X-ray crystallography and molecular dynamics simulations, we determined the Y269 residue acts to anchor the intercalating loop on abasic DNA. Atomic force microscopy reveals the Y269 residue is required for proper DNA bending by APE1, providing evidence for the importance of this mechanism. We conclude that this previously unappreciated tyrosine residue is key to anchoring the intercalating loop and stabilizing the DNA in the APE1 active site.

Background: Granuloma annulare (GA) is an inflammatory skin disorder. Localized GA is often self-resolving, but generalized GA is often recalcitrant to treatments. There are no targeted treatments for GA, largely due to lack of mechanistic understanding. Recently, tumor necrosis factor antagonism showed promise in GA, suggesting an underlying immune pathogenesis. Objective: To elucidate the immune pathogenesis and identify potential therapeutic targets for GA. Methods: Lesional and nonlesional skin biopsy samples were obtained from patients with GA and evaluated for a large array of inflammatory markers compared with inflammatory markers from normal skin of healthy individuals. Results: We found differential expression of many inflammatory genes compared with normal skin. These genes were associated with T-helper (Th) cell type 1/innate immunity (tumor necrosis factor-a, interleukin [IL]-1 beta, IL-12/23p40, signal transducer and activator of transcription 1, chemokine [C-X-C motif] ligand 9/10), Janus kinase signaling, and Th2 (IL-4, IL-31, chemokine (C-C motif) ligands 17 and 18; P < .05). Unexpectedly, IL-4 showed significant upregulation in GA lesional skin vs control skin (15,600-fold change). Limitations: Limited sample size. Conclusions: Our findings shed light on the inflammatory pathways of GA, supporting the notion that immune mechanisms could be driving disease, as suggested by the promising data of tumor necrosis factor-a inhibitors in GA. The significant Janus kinase and particularly Th2 signaling in GA advocates for the investigation of specific Janus kinase- and Th2- targeted drug therapy.

Molecular, cellular, and clinical studies of human inborn errors of immunity have revolutionized our understanding of their pathogenesis, considerably broadened their spectrum of immunological and clinical phenotypes, and enabled successful targeted therapeutic interventions. These studies have also been of great scientific merit, challenging a number of immunological notions initially established in inbred mice while revealing previously unrecognized mechanisms of host defense by leukocytes and other cells and of both innate and adaptive tolerance to self.