| November 2, 2011 |
JAX® Mice Strains Light up Your Research
In 2010, the interdisciplinary journal "Nature Methods" chose optogenetics as the "Method of the Year" across all fields of science and engineering (Wikipedia). What's optogenetics? It's a technology that combines genetics and optics to control and track – with split-second timing – specific events and functions of living cells, tissues, and organisms. Incorporated into mouse models, optogenetic technology is being used to map and analyze complex neural circuitries and to develop innovative therapies for many neurological disorders, including depression, narcolepsy, Parkinson's disease, blindness, addiction, and memory loss. Our glowing collection of diverse optogenetic mouse models is growing. Some of its features are described below.
Rhodopsin models
Our rhodopsin models are engineered to express light-sensitive ion channels called opsins, which are derived from either algae or archaebacteria, in specific brain cell populations. Opsins are transmembrane, retinal-binding proteins that combine a light-sensitive domain with an ion channel or pump. Using the right combinations of these mice and light wavelengths, you can turn on (light up) or turn off individual neurons.
Activation rhodopsin models. We distribute 15 activation rhodopsin models. Some contain opsins like channelrhodopsin 2 (ChR2, or COP4) from the algae Chlamydomonas reinhardtii. They are sodium ion channels and respond to blue light. When COP4-expressing neurons are stimulated by pulses of blue light of approximately 470nm, sodium ions flood the cells, depolarize them, and cause action potentials to fire. Some of our activation rhodopsin models contain COP4 variants engineered to contain mammalian codon replacements, gain-of-function mutations, endoplasmic reticulum (ER)-signaling motifs, or golgi-signaling motifs — all of which improve COP4 expression and/or make it more sensitive to certain absorption wavelengths. For example, the mhChR2 variant, also called hChR2 or ChR2(H134R), contains a gain-of-function H134R substitution that results in larger stationary photocurrents and wider light-activation spectral range (~450-490nm) than ChR2. The channelrhodopsin-1 (VChR1 or COP3) from the alga Volvox carteri is a green light-driven (~535nm) cation channel activation rhodopsin with a red-shifted action spectrum.
Distinct promoters have been used to drive expression of these proteins in specific neuronal populations.
 |
 |
| B6;SJL-Tg(Pvalb-COP4*H134R/EYFP)15Gfng/J (012355) expresses channelrhodopsin in the dorsal raphe nucleus, the interpeduncular nucleus and the gigantocellular reticular nucleus (Zhao et al. 2011). | B6.Cg-Tg(Chat-COP4*H134R/EYFP)6Gfng/J (014546) strongly expresses channelrhodopsin in the dorsal and ventral striatum, basal forebrain, facial nucleus, trochlear nucleus, and various other brainstem motor neuron nuclei (Zhao et al. 2011). |
Inhibition rhodopsin models. We distribute four inhibition rhodopsin models. They contain opsins that hyperpolarize cells and prevent action potentials from firing. Three express halorhodopsin (NpHR, or HOP), derived from the archaeobacterium Natronomas pharaonis. HOP is a chloride ion pump sensitive to yellow light of approximately 580nm. The fourth expresses archaerhodopsin-3 (Arch, aR-3, or AOP3), derived from the halobacterium Halorubrum sodomense. AOP3 is an outward proton pump sensitive to yellow light of approximately 575nm. Unlike light-driven chloride pumps that stay inactive for a long time in response to light, AOP3 spontaneously recovers from light-dependent inactivation.
Calcium and chloride sensors
One of our optogenetic mice, B6;129S-Gt(ROSA)26Sortm38(CAG-GCaMP3)Hze/J (014538), expresses the fusion protein GCaMP3, a calcium sensor. In the presence of calcium binding, the protein fluoresces brightly; in the absence of calcium binding, it fluoresces dimly. Three of our optogenetic models express the chloride sensor clomeleon, a fusion protein that contains CFP and YFP. When the chloride ion concentration is low, clomeleon's YFP component fluoresces; when the chloride ion concentration increases, YFP fluorescence decreases, and CFP fluorescence increases. By using an appropriate calibration curve, researchers can convert the ratio of YFP to CFP fluorescence to chloride ion concentration.
Cre-dependent strains
Several of our optogenetic mouse strains are Cre recombinase-dependent tool strains: when mated to mice that express Cre recombinase, they produce offspring that express an optogenetic effector protein. These mice can be used in combination with the wide variety of available Cre strains to generate mice that express an optogenetic protein of interest only in a specific neuronal population. To find an appropriate Cre mouse for your research, consult the "Cre Strains for Neurobiology" website — or a database of cre specificity at creportal.org.
Brighten your day. Check out our glowing collection of opotogenetic mouse models.
Drop by and talk to us at booth 1304 at the Neuroscience 2011 conference, November 12-16, in Washington, DC). Our poster, "A repository of mouse models for optogenetics research," will be on display on Tuesday, November 15, from 9:00-10:00 AM.
