Tanaka, K.F., et al. Cell Rep. 2, 397–406 (2012).

Light-sensitive microbial proteins are frequently used for manipulating the electrical activity of genetically defined cells in the brain and observing how such perturbations affect an animal's behavior. Several labs have generated transgenic mouse lines that express the light-sensitive proteins in a cell type–specific manner, but obtaining sufficiently high expression levels of the proteins in the desired cells for activity control has not been trivial. Working around this problem, Tanaka et al. have now generated a line of transgenic mice that expresses a highly light-sensitive version of channelrhodopsin-2 under the control of the tTA promoter. To obtain sufficiently high and reliable levels of the light-sensitive protein, the group inserted the transgene as a knock-in into the locus of the β-actin gene. These mice expand the existing repertoire of transgenic lines for optogenetic control that are based on bacterial artificial chromosome transgenics or the Cre-loxP system.