UPDATE : Bi-Directional Optogenetic Control

26 03 2010

The Deissseroth lab has released an updated version of their optical neuronal silencing gene Natronomonas halorhodopsin. In Molecular and Cellular Approaches for Diversifying and Extending Optogenetics, Gradinaru et al review current optogenetic methodology, and introduce eNpHR3.0-2A-ChR2, a genetic vector whose expression allows both action potential silencing and firing via illumination. This vector uses post-translational cleavage (via cis-acting hydrolase elements) of the 2A peptide to coexpress channelrhodopsin and halorohdopsin at high levels via a single promoter. The use of 2A provides a more balanced level of relative expression compared to the traditional strategy of using an IRES site, though differing degradation rates of the two proteins cause expression to not be truly stoichiometric.

eNpHR3.0 has superior cellular membrane expression

The improved eNpHR 3.0 contains additional trafficking sequences that greatly reduce expression in intracelluar compartments.  This results in enhanced surface expression a 20-fold increase in photocurrents over eNpHR1 and large, near-nanoampere currents at modest 3.5mW/mm^2 light intensities.  The paper implies superior performance over the Boyden group’s Arch optogenetic silencer technology, but shows no head to head data.  As always, testing both in your own system is the best way to evaluate their relative merits.

Activation spectrum for eNPAC (left), and for ChR2(H134R) (right, blue) and eNpHR3.0 (right, yellow) alone. Maximum eNPAC steady-state excitation was 567 ± 49 pA at 427 nm (n = 9), 62% of the value for ChR2(H134R) alone (916 ± 185 pA; n = 5). Similarly, maximum eNPAC inhibition was 679 ± 109 pA at 590 nm (n = 9), 61% of the value for eNpHR3.0 alone (1110 ± 333 pA; n = 4). Output power density for peak eNpHR3.0 current values was 3.5–5 mW/mm2 (3.5 mW/mm2 at 590 nm).

Gradinaru, V., Zhang, F., Ramakrishnan, C., Mattis, J., Prakash, R., Diester, I., Goshen, I., Thompson, K., & Deisseroth, K. (2010). Molecular and Cellular Approaches for Diversifying and Extending Optogenetics Cell DOI: 10.1016/j.cell.2010.02.037


Tang, W., Ehrlich, I., Wolff, S., Michalski, A., Wolfl, S., Hasan, M., Luthi, A., & Sprengel, R. (2009). Faithful Expression of Multiple Proteins via 2A-Peptide Self-Processing: A Versatile and Reliable Method for Manipulating Brain Circuits Journal of Neuroscience, 29 (27), 8621-8629 DOI: 10.1523/JNEUROSCI.0359-09.2009


A Better Neuronal Off-Switch

13 01 2010

Ed Boyden’s group has published High-performance genetically targetable optical neural silencing by light-driven proton pumps, detailing a set of new optical neuronal off-switches borrowed from various species that appear to be much better than Halorhodopsin for silencing neurons.  Halo works well for preventing action potentials when the nucleus is illuminated, but has a harder time blocking transmission of action potentials down an axon after it has been initiated. Also, previously engineered Halo variants, including eNpHR, suffer from light-dependent inactivation and have an expression sweet spot that could use broadening.  I’m looking forward to finding out if Arch, and the other new switches from Boyden’s group allow more powerful experiments in our hands.