Icariin Decreases the Expression of APP and BACE-1 and Reduces the β-amyloid Burden in an APP Transgenic Mouse Model of Alzheimer's Disease

Objective: The purpose of this study was to investigate the effects and pharmacological mechanisms of icariin, which is the main component in the traditional Chinese herb Epimedium, on β-amyloid (Aβ) production in an amyloid precursor protein (APP) transgenic (Tg) mouse model of Alzheimer''s disease (AD).Methods: APPV717I Tg mice were randomly divided into a model group and icariin-treated (30 and 100 μmol/kg per day) groups. Learning-memory abilities were determined by Morris water maze and object recognition tests. Aβ contents were measured by enzyme-linked immunosorbent assays and immunohistochemistry. Amyloid plaques were detected by Congo red staining and Bielschowsky silver staining. The levels of expression of APP and β-site APP-cleaving enzyme 1 (BACE-1) were measured by western blotting and immunohistochemistry.Results: Ten-month-old Tg mice showed obvious learning-memory impairments, and significant increases in Aβ contents, amyloid plaques, and APP and BACE-1 levels in the hippocampus. The intragastric administration of icariin to Tg mice for 6 months (from 4 to 10 months of age) improved the learning-memory abilities and significantly decreased the Aβ contents, amyloid plaques, and APP and BACE-1 levels in the hippocampus.Conclusion: Icariin reduced the Aβ burden and amyloid plaque deposition in the hippocampus of APP transgenic mice by decreasing the APP and BACE-1 levels. These novel findings suggest that icariin may be a promising treatment in patients with AD.     

山羊β乳球蛋白基因的克隆及其在转基因小鼠乳汁中的高效表达 Goat β-lactoglobulin Gene Cloning and High Expression in the Mammary Gland of Transgenic Mice

通过长距离PCR从山羊基因组DNA分两段扩增山羊β乳球蛋白（β-lactoglobulin,BLG）基因,扩增出的两个片段分别克隆到T载体上,利用BLG基因序列自身存在的NarI单酶切位点进行拼接,获得了全长为7.2kb的山羊BLG基因克隆,并构建了它的真核表达载体,经酶切鉴定和序列分析证实了克隆的正确性。用线性化的BLG基因显微注射小鼠受精卵以建立转基因鼠,经PCR和Southern印迹分析证实获得了6只首建者（Founder）转基因小鼠（3♀,3♂）,在泌乳期采集两只F0代转基因雌鼠乳汁并用ELISA测定山羊β乳球蛋白的含量,其表达水平分别为23.49 mg/mL和2.19 mg/mL。 Abstract:To clone goat β-lactoglobulin (BLG) gene,two fragments were amplified from goat genomic DNA by LD-PCR method.The fragments were inserted in T-vectors before being spliced into the whole 7.2 kb BLG gene at a single restriction enzyme site of NarI.Consequently,the eukaryotic expression vector was constructed.All the clones were proved to be correct by restriction enzyme cutting and sequencing analysis.Six Founders (3♀,3♂) of goat BLG transgenic mice were obtained by microinjection and BLG genes integration were confirmed by both PCR and Southern blot analyses.The milk was collected from two lactating female transgenic mice and goat BLG protein contents were measured with ELISA.The results showed that goat BLG protein in milk of the two mice were 23.49 mg/mL and 2.19 mg/mL,respectively.     

Cre重组酶表达载体的构建及其在转基因小鼠胰腺中的表达

组织特异性表达Cre重组酶的转基因小鼠是进行组织特异性条件敲除研究的关键。采用PCR扩增大鼠胰岛素基因705bp启动子指导发胰岛细胞中特异表达;同时采用改构的Cre重组酶基因,在其5'端添加有真核核糖体结合序列和核定位序列使Cre重组酶能穿越核膜在细胞核能发挥功能;同时,为了保证原核基因Cre能在真核系统顺利表达,在其3'端添加含内含子的人生长激素基因。构建的表达载体在去除原核序列后用显微注射方法转基因小鼠,在出生的27只仔鼠中,PCR检测共获得7只Cre整合阳性的转基因小鼠,整合率26％。这种Cre转基因小鼠与基因组小携带LoxP位点的条件基因打靶小鼠交配,在胰腺组织中可以检测到Cre介导的重组,表明Cre在转基因小鼠胰腺中有表达。     

动物基因工程三种诱导型表达系统及比较

诱导型基因表达系统已成为基因工程和病理学研究的重要工具。利用诱导型基因表达系统,可调控组织或细胞中重组基因在一定的时间里或一定的空间中表达,也能调控重组基因的表达水平。本文主要对近年来广泛应用的Cre/loxP、tet-off和tet-on三种诱导型基因表达系统的发展和应用进行综述。     

One-step knockin for inducible expression in mouse embryonic stem cells

Transgenesis enables the elucidation of gene function; however, constant transgene expression is not always desired. The tetracycline responsive system was devised to turn on and off transgene expression at will. It has two components: a doxycycline (dox)-controlled transactivator (TA) and an inducible expression cassette. Integration of these transgenes requires two transfection steps usually accomplished by sequential random integration. Unfortunately, random integration can be problematic due to chromatin position effects, integration of variable transgene units, and mutation at the integration site. Therefore, targeted transgenesis and knockin were developed to target the TA and the inducible expression cassette to a specific location, but these approaches can be costly in time, labor, and money. Here, we describe a one-step Cre-mediated knockin system in mouse embryonic stem cells that positions the TA and inducible expression cassette to a single location. Using this system, we show dox-dependent regulation of eGFP at the DNA topoisomerase 3β promoter. Because Cre-mediated recombination is used in lieu of gene targeting, this system is fast and efficient.     

A fast and efficient method for transiently transfecting ES cells: application to the development of systems for conditional gene expression

Classically, mouse embryonic stem (ES) cells are transfected by electroporation, a method that requires a large number of cells. Here we describe a protocol using a liposome based transfection agent that is a very simple, rapid and cost effective way of transiently transfecting very low numbers of ES cells. We found this method very useful in screening a large number of ES clones when working with inducible expression systems in which at least two elements are required for regulated expression of the gene of interest. After stable transfection of the first component, clones can be easily and rapidly screened for expression of the gene of interest by transiently transfecting the second component of the system using this protocol.     

Dorsal telencephalon-specific expression of Cre recombinase in PAC transgenic mice

The ability to restrict gene expression or disruption to specific regions of the brain would enhance understanding of the molecular basis for brain development and function. For this purpose, brain region-restricted promoters are essential. Here we report the isolation of a DNA fragment containing the Emx1 gene promoter, which is responsible for dorsal telencephalon-specific expression. The Cre recombinase gene was inserted into a mouse PAC (P1-derived artificial chromosome) Emx1-locus clone (PAC-Emx1#1 clone) and utilized to generate three transgenic mouse lines. In all three lines, especially Tg3, Cre-mediated recombination was highly restricted to Emx1-expressing cell lineages, from embryonic stages to adulthood. Immunohistochemical analyses showed that Cre protein is expressed in the dorsal telencephalon in all three lines in adulthood. Thus, the PAC-Emx1#1 clone contains essentially all regulatory elements necessary for Emx1 gene expression. Our results suggest that Emx1-Cre Tg3 mice and the PAC-Emx1#1 clone constitute powerful tools for dorsal telencephalon-specific gene manipulation.     

Temporal and tight hepatitis C virus gene activation in cultured human hepatoma cells mediated by a cell-permeable Cre recombinase

Hepatitis C virus (HCV) is not infectious in vivo exceptfor primates, so the proper HCV culture system andinbred animal model are difficult to set up, which has ham-pered detailed analysis on viral life cycle and pathogenesisof HCV infection [1,2]. Hepati…     

Mouse in red: red fluorescent protein expression in mouse ES cells, embryos, and adult animals

Spectral variants of green fluorescent protein are widely used in live samples for a broad range of applications: from visualization of protein interactions, through following gene expression, to marking particular cells in complex tissues. Higher wavelength emissions (such as red) are preferred due to the lower background-autofluorescence in tissues (Miyawaka et al., Nat Cell Biol Suppl S1-7, 2003). Until now, however, red fluorescent proteins (RFP) have displayed toxicity in murine embryos, which has hampered its application in this model. Here we report strong expression of a recently developed RFP variant, DsRed.T3, in mouse ES cells, embryos, and adult mice. Our results show that the red fluorescent wavelength has a superior tissue penetrance compared with spectral variants of lower wavelength. Furthermore, we have generated an ES cell line and a corresponding transgenic mouse line in which red fluorescence is activated upon Cre excision. Finally, we introduced cell type-specifically expressed Cre transgenes into this Cre recombinase reporter cell line, and by using the tetraploid embryo complementation assay, we could directly verify the Cre recombinase specificity on ES cell-derived embryos/animals.     

Selectable marker-free transgenic plants without sexual crossing: transient expression of cre recombinase and use of a conditional lethal dominant gene

Transgenic tobacco plants were produced that contained single-copy pART54 T-DNA, with a 35S-uidA gene linked to loxP-flanked kanamycin resistance (nptII) and cytosine deaminase (codA) genes. Retransformation of these plants with pCre1 (containing 35S transcribed cre recombinase and hygromycin (hpt) resistance genes) resulted in excision of the loxP-flanked genes from the genome. Phenotypes of progeny from selfed-retransformed plants confirmed nptII and codA excision and integration of the cre-linked hpt gene. To avoid integration of the hpt gene, and thereby generate plants totally free of marker genes, we attempted to transiently express the cre recombinase. Agrobacterium tumefaciens (pCre1) was cocultivated with leaf discs of two pART54-transformed lines and shoots were regenerated in the absence of hygromycin selection. Nineteen of 773 (0.25%) shoots showed tolerance to 5-fluorocytosine (5-fc) which is converted to the toxic 5-fluorouracil by cytosine deaminase. 5-fc tolerance in six shoots was found to be due to excision of the loxP-flanked region of the pART54 T-DNA. In four of these shoots excision could be attributed to cre expression from integrated pCre1 T-DNA, whereas in two shoots excision appeared to be a consequence of transient cre expression from pCre1 T-DNA molecules which had been transferred to the plant cells but not integrated into the genome. The absence of selectable marker genes was confirmed by the phenotype of the T₁ progeny. Therefore, through transient cre expression, marker-free transgenic plants were produced without sexual crossing. This approach could be applicable to the elimination of marker genes from transgenic crops which must be vegetatively propagated to maintain their elite genotype.