Activation of anthrachamycin biosynthesis in Streptomyces chattanoogensis L10 by site-directed mutagenesis of rpoB / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Genome sequencing projects revealed massive cryptic gene clusters encoding the undiscovered secondary metabolites in Streptomyces. To investigate the metabolic products of silent gene clusters in Streptomyces chattanoogensis L10 (CGMCC 2644), we used site-directed mutagenesis to generate ten mutants with point mutations in the highly conserved region of rpsL (encoding the ribosomal protein S12) or rpoB (encoding the RNA polymerase β-subunit). Among them, L10/RpoB (H437Y) accumulated a dark pigment on a yeast extract-malt extract-glucose (YMG) plate. This was absent in the wild type. After further investigation, a novel angucycline antibiotic named anthrachamycin was isolated and determined using nuclear magnetic resonance (NMR) spectroscopic techniques. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis and electrophoretic mobility shift assay (EMSA) were performed to investigate the mechanism underlying the activation effect on the anthrachamycin biosynthetic gene cluster. This work indicated that the rpoB-specific missense H437Y mutation had activated anthrachamycin biosynthesis in S. chattanoogensis L10. This may be helpful in the investigation of the pleiotropic regulation system in Streptomyces.

Beneficial effects of liver X receptor agonist on adipose-derived mesenchymal stem cells transplantation in mice with myocardial infarction / 中华心血管病杂志

<p><b>OBJECTIVE</b>To investigate the effects of liver X receptor (LXR) agonist on adipose-derived mesenchymal stem cells (AD-MSCs) implantation into infarcted hearts of mice.</p><p><b>METHOD</b>AD-MSC(Fluc+) which stably expressed firefly luciferase (Fluc) were isolated from β-actin-Fluc transgenic mice and characterized by flow cytometry. Male FVB mice were randomly allocated into the following four groups (n = 10 each): (1) sham group; (2) MI + PBS group; (3) MI + AD-MSC(Fluc+) group; (4) MI + AD-MSC(Fluc+) + LXR agonist (T0901317) group. AD-MSC(Fluc+) or PBS were injected intramyocardial into peri-infarcted region of mice heart after permanent left anterior descending (LAD) artery ligation. Bioluminescence imaging (BLI) was performed for quantification of injected cells retention and survival. Cardiac function was evaluated by echocardiography.</p><p><b>RESULTS</b>The AD-MSC(Fluc+) were positive for CD44 and CD90 by flow cytometry. BLI evidenced the firefly luciferase expression of AD-MSC(Fluc+) which was positively correlated with cell numbers (r(2) = 0.98). The results of BLI in vivo revealed that LXR agonist could improve the survival of AD-MSC(Fluc+) at day 7, 14 and 21 after transplantation compared with AD-MSC(Fluc+) alone group. Cardiac function was further improved in combination therapy group compared with AD-MSC(Fluc+) alone group (P < 0.05).</p><p><b>CONCLUSIONS</b>LXR agonist T0901317 can improve the retention and survival of intramyocardial injected AD-MSC(Fluc+) post-MI, and the combination therapy of T0901317 and AD-MSC(Fluc+) has a synergetic effect on improving cardiac function in this model.</p>