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[求助]
关于jacksonlab上的转基因小鼠，上的说明
Hemizygous Six2-TGCtg mice are viable and fertile, harboring a BAC transgene with a Tet-off-eGFPCre under control of the Six2 promoter/enhancer regions within the BAC transgene. The Tet-off-eGFPCre contains both the tetracycline-controlled transactivator protein (tTA) as well as the tetracycline operator (tetO; also called tetracycline-responsive element [TRE] or tet-operator) upstream of an EGFPCre fusion protein. Sequence updates published after this transgene was created revealed an upstream Six2 ATG start site that is in-frame with the tTA; thus an apparent and unintended fusion was created with the tTA (80 amino acids potentially added) that renders transgene expression unaffected by tetracycline/doxycycline administration. It is not known whether the "mutant" tTA is resistant to tetracycline/doxycycline inactivation and still binds to TRE to activate EGFPCre expression or if the TRE acts as a minimal promoter adjacent to the Six2 promoter in the presence of a nonfunctional tTA. Either way, Tet-independent expression of the eGFPCre fusion protein (EGFP immunofluorescence and direct fluorescence/Cre recombinase activity) is directed to nephron progenitor population cap mesenchyme from the onset of metanephric kidney development. When bred with mice containing a loxP-flanked sequence of interest, Cre-mediated recombination will result in deletion of the floxed sequence(s) in such tissues of the offspring. While not useful as a Tet-Off tool, these Six2-TGCtg mice may be useful as fluorescent or Cre-lox tools for lineage-tracing/marking Six2-expressing cells for studying multipotent nephron progenitor cell populations throughout kidney organogenesis. The donating investigator reports they were unable to produce homozygous mice from hemizygous matings.
英文中下划线部分，我的理解是six2这个启动子可以带动egfp-cre的表达，但是四环素对它没有影响，不理解的是为什么要加入tet-off系统？然后四环素又对此没有作用？谢谢各位虫友解答！ |
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