Figure 1.

Tet system. (A) Tet system requires two mouse lines. The first is a mouse line expressing gene encoding tetracycline transactivator (tTA) protein under the control of cell-type specific promoter. The second is one expressing the functional probe (such as ChR2) connected downstream of the tetO promoter. Targeted tTA::tetO double transgenic mouse is generated by mating. (B) The functional probe is expressed in tTA-positive cells, but not in tTA-negative cells in tTA::tetO double transgenic mouse. In tTA-positive cells, tTA binding to the tetO promoter triggers the transcription, which results in the cell-type specific expression of ChR2. TetO is the cassette containing the tetracycline operon site (multiple closed squares) and CMV minimal promoter (circle P). ChR2: channelrhodopsin 2, tetO: tet operator, tet system: tetracycline-controllable gene expression system, tTA: tetracycline transactivator.