Experimental Animal Division

KENGE-tet enables us to achieve sufficient opsin expression to trigger photocurrents in combination with existing cell type-specific tTA lines. All pictures show tTA-mediated ChR2-EYFP induction by KENGE-tet.

Optogenetic strategies for controlling neuronal activity have been employed widely for mapping functional circuits within the nervous system. Channelrhodopsin-1 (ChR1) and ChR2, related microbial-type rhodopsins from Chlamydomonas reinhardtii, are involved in the generation of photocurrents. ChR2 is a light-gated cation channel, whereas ChR1 is a light-gated proton channel. The N-terminal 315 amino acids of ChR2 are homologous to the seven trans-membrane structure of numerous microbial-type rhodopsins. Inward currents in ChR2-expressing cells can be evoked after a flash of blue light in the presence of all-trans retinal [1, 2].

Drs. Tanaka and Yamanaka established the Knockin-mediated ENhanced Gene Expression by improved tetracycline-controlled gene induction (KENGE-tet) system for reliable generation of transgenic mice with light-responsive cells. They achieved this through targeting transgene insertion just downstream of the β-actin gene polyadenylation signal and through generating tetO-ChR2(C128S)-EYFP knock-in mice by homologous recombination of embryonic stem cells. They then demonstrated that ChR2(C128S)-mediated inward currents resulted in c-fos mRNA induction in astrocytes, showing that the KENGE-tet system is applicable to the optogenetic manipulation of both excitable neurons and non-excitable glial cells [3]. The results show that their system is applicable not only to neuroscience but also to any biomedical study requiring an understanding of how the activity of a selected population of cells is propagated through intricate organic systems.