Cell ablation in which specific cells are killed on demand has been a useful tool for biologists trying to understand cell function. Makhijani et al (2017) in a recent paper in Cell Chemical Biology describe their development of an optogenetic cell ablation tool that they use in insects.
Cell lineage studies in development and neurobiology studies looking at neuron function have been notable beneficiaries of cell ablation technologies and in particular genetic cell ablation in which cells are killed by triggering apoptosis, expression of a toxin or some other cell lethal action. For example, misexpression of the pro-apoptotic gene reaper Drosophila cells leads to their death.
Not long ago the use of an optogenetic cell ablation system was described in C. elegans that was based on a ‘mini singlet oxygen generator’ or miniSOG.
miniSOG is a green fluorescent protein which when illuminated by blue light (450nm) will result in the production of reactive oxygen species, leading to cell damage that can be lethal.
Makhijani et al (2017) demonstrate the use of miniSOG as a light actuated cell ablation tool. Actually, they did not use miniSOG but miniSOG2, an evolved and improved version of miniSOG the authors created. A comparison of miniSOG and miniSOG2 reveals seven mutations, four of which surround the chromophore – flavin mononucleotide (FMN).
The authors demonstrate the functionality and improved performance of miniSOG2 compared to miniSOG in mammalian cells and in transgenic Drosophila.
In cultured cells miniSOG2 resulted in faster responses following illumination with responses (measured in caspase expression levels) occurring after only 60 seconds of illumination and this lead to high levels of response in 4 hours.
In Drosophila the authors use a number of cell and tissue specific Gal4 drivers to drive minoSOG2 in a population of neurons in the larva and in cells of the developing imaginal wing discs. In both cases cell death resulted, as was expected based on the cells that were expressing miniSOG2 and were illuminated.
Blue light does not penetrate tissues very much and the clear cuticle of Drosophila larvae make this system practical. Its use in adults may be more limited.
The source of blue light seemed to matter as well with light from a xenon lamp being quite effective while light from scanning lasers were inefficient inducers of cell death.
Optogenetic cell ablation will be a useful tool beyond Drosophila. Indeed conditional lethal genetic systems are growing in demand and optogenetic cell and tissue ablation may provide needed options that go beyond teton/off systems and ‘runaway transcription’
Makhijani, K, To, T-L, Ruiz-González, R, Lafaye, C, Royant, A, Shu, X. Precision Optogenetic Tool for Selective Single- and Multiple-Cell Ablation in a Live Animal Model System. Cell Chemical Biology. doi 10.1016/j.chembiol.2016.12.010