Stimulatory effect of polyethylene glycol (PEG) on gene expression in mouse liver following hydrodynamics-based transfection

Diverse Response Pattern to Anoxia in Three Freshwater Turtle Species

With increasing water eutrophication and global warming, anoxia and hypoxia are becoming more and more common in water environments. Most vertebrates have a limited tolerance to anoxia of only a few minutes, but some species, such as turtles, can survive for months being exposed to anoxia. Antioxidant defense systems may have a potential role in resisting anoxia stress in freshwater turtles. The three-keeled pond turtle Chinemys reevesii, the snapping turtle Chelydra serpentina and the soft-shelled turtle Pelodiscus sinensis are three popular aquaculture species and share similar habitats in China. While C. reevesii and C. serpentina are hard-shelled turtles with poor skin permeability, P. sinensis is soft-shelled turtle whose skin permeability is good. We examined the antioxidant defense responses in different tissues of the three turtle species under acute anoxia stress for 10 h and subsequently recovered for 24 h in order to reveal the response patterns of the antioxidant defense system of the three turtle species that differed in morphological structure and life history strategy. We found that the antioxidant response patterns to acute anoxia stress were tissue- and species-specific. The soft-shelled turtle was more sensitive to anoxia than the hard-shelled turtles. Under anoxia stress, the three species kept the activities of most antioxidant enzymes stable. C. reevesii and P. sinensis were highly dependent on vitamin C in antioxidant defense, while high activities of structural antioxidant enzymes were found in the tissues of C. serpentina. The above diverse patterns may be related with adaptive evolution of morphological structure and physiological functions of the three turtle species.

Adenovirus mediated expression "in vivo" of the chemokine receptor CXCR1

A major hurdle in the structural analysis of membrane proteins is the expression of a functional and homogeneous form of the protein. Except for rhodopsin, most G protein-coupled receptors (GPCRs) are endogenously expressed at very low levels. Heterologous expression of GPCRs in bacteria, yeast, insect cells or mammalian cell lines often yields proteins with large amounts of misfolded proteins and heterogeneous posttranslational modifications. Here, we report a novel mammalian "in vivo" system for the expression of the chemokine receptor CXCR1. This receptor was expressed in liver of mice infected with adenovirus encoding CXCR1. Liver plasma membranes from infected mice displayed high-levels of (125)I-labeled human interleukin-8 (IL-8) binding. The pharmacological profile of the recombinant CXCR1 expressed "in vivo" was similar to those expressed in neutrophils. We found that the incorporation of the detergent solubilized CXCR1 into phospholipid vesicles in the presence of Gi/Go proteins is required for the reconstitution of (125)I-IL-8 binding. On the basis of the presence of the several endogenous His residues and glycosylation moieties in CXCR1 we fractionated the detergent-solubilized plasma membranes by employing Ni- and Concanavalin A-based chromatography. Fractions enriched with CXCR1 were monitored by (125)I-IL-8-bound to the receptor and Western blots with anti-CXCR1 antibodies. This robust expression system could be readily applied for the expression of GPCRs and other eukaryotic membrane proteins.

Cre-loxP system as a versatile tool for conferring increased levels of tissue-specific gene expression from a weak promoter

Attempts to image reporter gene expression driven by weak promoters are often hampered by the poor transcriptional activity of such promoters. Most tissue-specific promoters are weak compared with stronger but constitutively expressing viral promoters. In this study, we validated methods of enhancing the transcriptional activity of weak promoters using a Cre-loxP system in vitro and in vivo. We constructed a tester vector, pCTL, which carries a strong systemic cytomegalovirus enhancer/chicken beta-actin promoter (CAG), loxP-flanked CAT, and firefly luciferase (luc) cDNAs. Herpes simplex virus-thymidine kinase (HSV-tk) promoter was used as a weak and systemic promoter and ligated to Cre for construction of pTC. Luc activity was higher (about 10-fold enhancement) in co-transfected (with pCTL and pTC) than in singly (with HSV-tk promoter-driven luc expression vector pTL) transfected NIH3T3 cells. In vivo electroporation-mediated gene delivery of both pCTL and pTC into murine oviductal epithelium yielded results (about 16-fold enhancement) similar to those obtained with in vitro-transfected NIH3T3 cells. To evaluate tissue-specific enhancement of gene expression, podocyte (glomerular visceral epithelial cell)-specific nephrin promoter was ligated to the Cre gene or luc cDNA to create pNC and pNL, respectively. We achieved 2.4-fold improvement of luc gene expression in the mouse kidney in vivo when pCTL and pNC were co-transfected via the tail vein via the lipoplex method. The combination of a weak tissue-specific promoter with the Cre-loxP system could thus be used to enhance the strength of tissue-specific promoters in vitro and in vivo.