12 research outputs found

    Blends of Linear and Long-Chain Branched Poly(l‑lactide)s with High Melt Strength and Fast Crystallization Rate

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    The long-chain branched polylactides (LCB-PLAs) prepared by coupling the hydroxyl-terminated two-arm (linear) and triarm PLA prepolymers of identical arm length with hexamethylenediacianate (HDI) were used to improve the melt rheological and crystallization properties of linear polylactide resin, PLA 4032D from NatureWorks. The blends containing LCB-PLA displayed higher zero shear viscosities, more significant shear shinning, more melt elasticity, and much longer relaxation times together with significant strain hardening in elongational deformation. <i>T</i><sub>g</sub>, <i>T</i><sub>m</sub> and crystallinity (<i>X</i><sub>c</sub>) of linear PLA remained virtually unaffected, but the crystallization rate increased obviously, since the branch points of LCB-PLAs could play a role of nucleating agent. High melt strength, fast crystallization, and favorable miscibility improved the foaming ability of the linear/LCB-PLA blends, substantially

    Rheology and Crystallization of Long-Chain Branched Poly(l‑lactide)s with Controlled Branch Length

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    A series of long-chain branched poly­(l-lactide)­s (LCB-PLAs) with controlled branch length were prepared by a simple and efficient method through a combination of ring-opening polymerization (ROP) of l-lactide and a coupling reaction between the terminal OH groups of the PLA prepolymers and the NCO groups of HDI. The influences of reaction conditions on the synthesis of the LCB-PLAs were investigated, and the structures of the resultant LCB-PLAs were characterized by <sup>1</sup>H NMR spectroscopy and SEC-MALLS. By adjusting the degree of polymerization and the composition of the prepolymers, LCB-PLAs with different branch densities and molecular weights between branch points were obtained. The effect of macromolecular chain branching on the rheology and crystallization of PLA was also investigated. The LCB structure contributed to the enhancement of the zero-shear viscosity, complex viscosity, storage modulus, melt strength, and strain hardening under elongational flow. Thermal behavior indicated that the branch structure resulted in a short nucleation induction period and more rapid crystallization, which can be a guarantee of high-strength foams

    Role of Histone Deacetylases in Gene Regulation at Nuclear Lamina

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    <div><p>Theoretical models suggest that gene silencing at the nuclear periphery may involve “closing” of chromatin by transcriptional repressors, such as histone deacetylases (HDACs). Here we provide experimental evidence confirming these predictions. Histone acetylation, chromatin compactness, and gene repression in lamina-interacting multigenic chromatin domains were analyzed in Drosophila <em>S2</em> cells in which B-type lamin, diverse HDACs, and lamina-associated proteins were downregulated by dsRNA. Lamin depletion resulted in decreased compactness of the repressed multigenic domain associated with its detachment from the lamina and enhanced histone acetylation. Our data reveal the major role for HDAC1 in mediating deacetylation, chromatin compaction, and gene silencing in the multigenic domain, and an auxiliary role for HDAC3 that is required for retention of the domain at the lamina. These findings demonstrate the manifold and central involvement of class I HDACs in regulation of lamina-associated genes, illuminating a mechanism by which these enzymes can orchestrate normal and pathological development.</p> </div

    Effect of HDAC depletion on retention of the 60D1 locus at the nuclear periphery.

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    <p>(<b>A</b>) Position of the locus was determined by FISH (red) and the nuclear envelope visualized with immunostaining for <i>LamDm<sub>o</sub></i> (green). Figure shows representative nuclei of cells treated with control <i>LacZ</i> dsRNA or a mixture of <i>HDAC1</i> and <i>HDAC3</i> dsRNAs. (<b>B</b>) Bars show the proportion of nuclei with FISH signals ≤0.4 µm apart from the nuclear envelope. dsRNAs used for depletion are indicated below the X-axis. <i>LacZ</i>, n = 256, 3 independent experiments; <i>HDAC1</i>, n = 199, 2 independent experiments; <i>HDAC3</i>, n = 201, 2 independent experiments; <i>HDAC1</i>+<i>HDAC3</i>, n = 208, 2 independent experiments; <i>LamDm<sub>o</sub></i>, n = 89, 2 independent experiments. Error bars show SEM. *, p≤0.05 for comparisons to <i>LacZ</i> control.</p

    Effects of Class I HDAC depletion on histone acetylation and chromatin compactness.

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    <p>(<b>A</b>) ChIP assay shows increased acetylation of histones H3 (left panel) and H4 (right panel) in cells treated with <i>HDAC1</i> dsRNA and <i>HDAC3</i> dsRNAs as compared to the <i>LacZ</i> dsRNA-treated control cells. n = 4; error bars represent SEM. (<b>B</b>) Decreased chromatin compactness revealed by the general sensitivity to DNase I assay in <i>HDAC1</i> dsRNA-treated cells as compared to the control <i>LacZ</i> dsRNA treatment. Gene positions are shown below the X-axis with the <i>60D1</i> cluster framed. n = 2 to 4; error bars show SEM. *, p≤0.05; **, p≤0.01; ***, p≤0.001 for comparisons to the control. Inserts show the knockdown efficiency of the RNAi at the RNA levels.</p

    Nanoplastics Shape Adaptive Anticancer Immunity in the Colon in Mice

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    The impact of nanoplastics (NPs) on human health is still not well understood, and more research is needed to better understand the risks associated with these particles. In this study, we found that oral administration of polyethylene (PE) NPs in a mice model significantly disrupted the intestinal microenvironment, which shapes adaptive immune response and favors the established in situ colorectal tumor growth. Using single-cell RNA sequencing technology, we show that NPs triggered colon IL-1β-producing macrophages by inducing lysosome damage, leading to colonic Treg and Th17 differentiation associated with T cell exhaustion, which creates a colon environment that favors the tumor initiation and progress. A similar effect is also observed in polystyrene NPs. Our result provides insight into the potential link between NPs ingestion and colon tumorigenesis, and the urgency of addressing plastic pollution worldwide

    Effect of Class I HDAC depletion on expression of the <i>60D1</i> gene cluster.

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    <p>(<b>A</b>) Treatment of cells with <i>HDAC1</i> dsRNA results in increased transcript levels for the testis-specific cluster. Bars show changes in transcript levels detected with RT-qPCR in cells treated with <i>HDAC1</i> dsRNA or <i>HDAC3</i> dsRNA, as compared to the <i>LacZ</i> dsRNA-treated control cells. (<b>B</b>) Increased changes in transcript levels upon treatment of the cells with the mixture of <i>HDAC1</i> and <i>HDAC3</i> dsRNAs. Gene symbols are shown on the X-axis; the <i>60D1</i> gene-cluster is framed. <i>Rp49</i> and <i>Actin5C</i> are housekeeping genes used as controls. <i>Rpl9</i> served as a template for loading reference. n = 6 to 9; error bars show SEM; **, p≤0.01; ***, p≤0.001 for comparison of individual transcript levels between <i>LacZ</i> RNAi and target RNAi; †††, p≤0.001 for comparison between the <i>60D1</i> cluster and control housekeeping genes. Inserts show the knockdown efficiency of the RNAi at the RNA levels.</p