Inducible knockdown

Unlike the Gre/loxP system, the tetR/O switch is not dependent on enzyme-based DNA rearrangements but is controlled by the small synthetic compound doxycycline (Dox). In the absence of Dox the tetracycline repressor (tetR), expressed from a constitutive promoter, binds to the tet operator (tetO) within a modified HI promoter and blocks shRNA transcription (Fig. 3b). Exposure to Dox dissociates the tetR from tetO which enables shRNA expression from the HI promoter (22). Thus, gene silencing is induced by Dox addition (20, 22, 23). This system is successfully in use to validate the potential of candidate drug targets in vivo (24-28). A commercial service for the production of Dox inducible knockdown mice and rats is available from Taconic (see www. taconic.com). 

The properties of DNA-AuNPs have also proven useful in nanotherapeutics as antisense materials. These materials can easily transfect a variety of cell types without causing toxicity. Due to the enhanced binding properties of DNA-AuNPs, they act as efficient scavengers of mRNA and induce knockdown of a target gene via an antisense therapeutic mechanism in vitro. The fumre direction and progress of these materials as therapeutics will be highly dependent on how these materials are processed in vivo and if these materials can be eliminated from the body. 

Fenpyroximate exhibits acaricidal and knockdown activities on phytophagous mites, such as Tetranychus urticae Koch (two-spotted spider mite) and Panony-chus citrP in citrus, apple, pear, peach, grape, etc. Fenpyroximate inhibits the mitochondrial NADH-Co Q reductase, which induces a decrease in ATP content and morphological changes in mitochondria and ultimately shows the acaricidal and knockdown activities. ... 

The siRNAs assemble into a complex called RNA-induced silencing complex (RISC) and unwind in the process. The single stranded siRNAs then attach to complementary RNA molecules, thus targeting these RNAs for destruction—a process that is called gene knockdown. 

The absence of a transactivation-competent NF-kB heterodimer in the nucleus of latently infected resting memory CD4+ T cells could contribute to latency. Activation of the NF-kB pathway leading to migration of a transactivating heterodimer such as p50/p65 could allow viral reactivation. In the absence of induction, NF-kB p50-HDACl complexes constitutively bind the latent HIV-1 LTR (Williams et al, 2006). NF-kB p50 does not possess a transactivation domain. These p50-HDACl complexes induce histone deacetylation and repressive changes in chromatin structure of the HIV-1 LTR (Williams et al, 2006). Knockdown of p50 expression reduces HDACl binding to the latent HIV-1 LTR and induces RNA polymerase II recruitment (Williams et al, 2006). Concomitantly with HIV-1 transcriptional activation, the p65 subunit and different HATs are recruited to the viral promoter (Lusic et al, 2003 Thierry et al, 2004). 

Lysine methyltransferases have been linked in various cases to the pathogenesis of cancer. Examples can be found for KMTs that induce repressive marks as well as for those that lead to an activating methylation pattern. Possible reasons for a disturbed regulation of methylation may result in mutations of enzymes or overexpression in cancer cells. An indication for a therapeutic benefit of potential inhibitors is often derived from siRNA knockdown of the requisite isotype. Mutations of MLLl for example are thought to be responsible for various forms of acute leukemia [63]. Overexpression of EZH2 was linked to breast or prostate cancer [64] and increased levels in human cancers have also been observed for G9a. Increased mRNA levels for... 

A detailed protocol for the generation of genetically modified human xenograft mouse models in which the knockdown of a putative oncology target is temporally regulated in vivo using a tetracycline inducible system is found in this book (17). 

Stable Integration of Doxycycllne-Inducible shRNA Vectors Into ES Cells by RMCE and Generation of Knockdown Mouse Lines... 

Subheading 3.1.3, step 5 The knockdown has to be induced by cultivating the cells for 2 days with medium containing 1 pg/ ml doxycycline before harvesting (see Notes 10 and 11). 

Reversible gene knockdown in mice using a tight, inducible shRNA expression system. Nucleic Acids Res 35 e54... 

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