Looks like there has been some new results in the field of photoactivated transcription. Unlike the fully genetically-encoded systems reviewed in a Journal Club, this uses a hybrid genetic and small molecule approach. In Doxycycline-dependent photoactivated gene expression in eukaryotic systems, Cambridge et al. add the photolabile protecting groups to doxycyclin derivatives, which then function as photoactivatable switches in the commonly used Tet-on system. Dr. Dan O’Connor described the technique as “the path of least resistance to photoactivated transcription.”
Local (left) and global (right) GFP expression following optical uncaging of cyanodoxycyclin
The authors were able to get robust gene expression with standard UV irradiation, but also were able to uncage sufficient cyanodoxycycline with two-photon illumination to cause highly localized gene expression in cultures. In live tadpoles, they stuck to UV for the greater efficiency.
The standard caveats of the tet system apply. The off-state still has a bit of residual gene expression, which is fine for some applications (like fluorescent tagging), and a dealbreaker for others (cre induction). Drug delivery takes time and comes with diffusion, penetration and clearance issues. UV penetration through deep tissue is going to be a big technical hurdle to overcome to apply this to full-grown mammals. Blasting living tissue with high power UV usually isn’t a good idea. Despite these caveats, the system clearly works and I’d bet the authors are already applying the system to some next-step applications and biological questions. The potential of selectively turning on genes in functionally identified neurons via light is enormous. It is one of the most likely eventual avenues into possible optical activation or suppression of specific thought patterns (at least if you are willing to squirt virus into your brain and eat a bunch of nasty antibiotics).
Brain Windows 
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