Hemizygous TRE-Bi-SG-T line 1.1 transgenic mice are viable and fertile, with no reported phenotypic abnormalities. The TRE-Bi-SG-T transgene has Myc-tagged tdTomato and full-length mouse synaptophysin/mut4EGFP fusion protein (Syp-GFP) expression under the control of the bi-directional tet-responsive promoter (tetO or TRE). When bred with another mouse expressing tetracycline-controlled transactivator protein (tTA) or reverse tetracycline-controlled transactivator protein (rtTA), tdTomato and Syp-GFP fusion protein expression can be regulated with the tetracycline analog doxycycline (dox) in the resulting double mutant offspring. In tTA(-dox) or rtTA(+dox)-expressing cells, tdTomato expression is directed to the entire cell, while GFP expression is directed to the synapse/synaptic vesicle. The donating investigator reports that direct GFP fluorescence and direct tdTomato fluorescence may be visualized in these mice when tTA is present/dox is absent. In addition, the three Myc epitopes at the C-terminus of tdTomato allow fluorescent signal enhancement via immunofluorescence if needed. These TRE-Bi-SG-T transgenic mice are useful to generate mutant mice for Tet-Off/Tet-On and/or fluorescent protein applications.

These TRE-Bi-SG-T transgenic mice may be used to design a tripartite system to express fluorescently tagged synaptic proteins with both spatial and temporal control. When bred with floxed-STOP-tTA mice (ROSA26-ZtTA; Stock No. 012266), the resulting double mutant mice allow tdTomato and Syp-GFP expression to be determined by the tissue-specific Cre recombinase expression of a third strain of the researchers choosing. For example, when TRE-Bi-SG-T transgenic mice are bred with floxed-STOP-tTA mice (ROSA26-ZtTA; Stock No. 012266) and a neural-specific Cre recombinase strain (for example: Foxg1-Cre; Stock Nos. 004337 or 006084), the resulting triple mutant mice should exhibit labeling of whole neurons in red and presynaptic terminals in green in the absence of dox.