|専攻分野||Brain function analysis|
For the last decade, I have focused on the structure-function analysis of channelrhodopsins (ChRs) in microalgae. Why do we need to study ChRs in neuroscience? ChRs gained attention as useful tools for controlling neuronal activity with light and established a new research field in neuroscience called “optogenetics”. As one of the founders of optogenetics, I would like to contribute to the development of optogenetics and solve the basic principles of brain function in learning, memory, and mental processes using new technologies with light.
Honjoh, T., Ji, Z.-G., Yokoyama, Y., Sumiyoshi, A., Shibuya, Y., Matsuzaka, Y., Kawashima, R., Mushiake, H., Ishizuka, T., and Yawo, H. (2014). Optogenetic patterning of whisker-barrel cortical system in transgenic rat expressing channelrhodopsin-2. PLoS ONE 9, e93706.
Umeda, K., Shoji, W., Sakai, S., Muto, A., Kawakami, K., Ishizuka, T., and Yawo, H. (2013). Targeted expression of a chimeric channelrhodopsin in zebrafish under regulation of Gal4-UAS system. Neurosci. Res. 75, 69–75.
Tanimoto, S., Sugiyama, Y., Takahashi, T., Ishizuka, T., and Yawo, H. (2013). Involvement of glutamate 97 in ion influx through photo-activated channelrhodopsin-2. Neurosci. Res. 75, 13–22.
Egawa, R., Hososhima, S., Hou, X., Katow, H., Ishizuka, T., Nakamura, H., and Yawo, H. (2013). Optogenetic Probing and Manipulation of the Calyx-Type Presynaptic Terminal in the Embryonic Chick Ciliary Ganglion. PLoS ONE 8, e59179.
Asano, T., Ishizua, T., and Yawo, H. (2012). Optically controlled contraction of photosensitive skeletal muscle cells. Biotechnol. Bioeng. 109, 199–204.
Ji, Z.-G., Ito, S., Honjoh, T., Ohta, H., Ishizuka, T., Fukazawa, Y., and Yawo, H. (2012). Light-evoked somatosensory perception of transgenic rats that express channelrhodopsin-2 in dorsal root ganglion cells. PLoS ONE 7, e32699.
Wen, L., Wang, H., Tanimoto, S., Egawa, R., Matsuzaka, Y., Mushiake, H., Ishizuka, T., and Yawo, H. (2010). Opto-current-clamp actuation of cortical neurons using a strategically designed channelrhodopsin. PLoS ONE 5, e12893.
Wang, H., Sugiyama, Y., Hikima, T., Sugano, E., Tomita, H., Takahashi, T., Ishizuka, T., and Yawo, H. (2009). Molecular determinants differentiating photocurrent properties of two channelrhodopsins from chlamydomonas. J. Biol. Chem. 284, 5685–5696.
Ishizuka, T., Kakuda, M., Araki, R., and Yawo, H. (2006). Kinetic evaluation of photosensitivity in genetically engineered neurons expressing green algae light-gated channels. Neurosci. Res. 54, 85–94.
The Japan Neuroscience Society
Channelrhodopsins (ChRs) are light-gated cation channels that were originally isolated from the green alga, Chlamydomonas reinhardtii. In the organism, a light signal is converted into an electrical one in a single molecule. When these molecules are exogenously expressed in mammalian neurons, they become photosensitive and blue LED illumination of the photosensitive neurons is enough to evoke action potentials in a pulse-to-pulse manner. The new technology, controlling neuronal activity with light, is termed “optogenetics”. ChR2 is widely used for controlling activity of genetically and spacially defined neurons with temporally precise manipulation in a wide range of model animals, but it is still required to improve the properties of this technique, such as poor expression ChRs on cell membranes, small conductance, large desensitization, and the optimal excitation wavelength. To overcome these disadvantages of ChR2, we have focused on the distinct properties of ChR1 and ChR2 and have prepared chimeric molecules by replacing the N-terminal segments of ChR2 with the homologous counterparts of ChR1, and have analyzed their photocurrent properties. Some of the chimeras (ChRFR and ChRWR in the figure) have several advantages over the wild-type ChR2 for the reliable induction of light-induced depolarization of neurons.
ChRs are the first and so far unique light-gated cation channels. Despite the numerous applications in neuroscience, the functional mechanism of ChR is still not well-understood. Structure-function analysis of ChRs is beneficial not only for our understanding of the functional mechanism of ChR at the molecular level but also for creating new optogenetic tools that would provide technological innovations in neuroscience.