CRISPy Circuits

Sophisticated tools for genome modification allow investigators to devise ever-increasing complex genetic circuits.

The Gal4 /UAS system is one example of a simple binary system.

This is an AND circuit.  Inputs 1 AND 2 are needed for an output. from http://www.kurzweilai.net/the-most-complex-synthetic-biology-circuit-yet

This is an AND circuit. Inputs 1 AND 2 are needed for an output. from http://www.kurzweilai.net/the-most-complex-synthetic-biology-circuit-yet

While powerful, this system does not allow for particularly complex genetic circuits to be assembled.

Four Logic Gates or Switches that provide outputs under different conditions.

Four Logic Gates or Switches that provide outputs under different conditions.

 

 

 

 

As Kiani et al (2014) state in their recent paper in Nature Methods, ‘A key obstacle to creating sophisticated genetic circuits has been the lack of scalable device libraries.’ By that they mean we do not have enough regulatory systems like Gal4 /UAS that can be interconnected to make a collection of input/output devices that can then be interconnected to form a complex circuit.  The figure below shows how 4 binary systems in bacteria can be used to create a 4-input AND circuit.  But to add complexity to this, ie. to scale this up, you would need to find more araC- or lacI- or luxR- or tetR-like systems.  But what if you could make as many of those systems as you wanted, ie. is scalable?  Kiani et al. describe how the CRISPR/Cas9 system can be used for this purpose.

Kiani et al. (2014) report on their efforts to use the CRISPR/Cas9 to begin to assemble complex circuits. One interesting innovation was the development of strategies for expressing gRNA from Pol II promoters and this could be adopted by insect biologists. The scalability of this system is also pretty interesting

Kiani et al (2014) describe the design and creation of two simple circuits in human cells.

This is a 4-input AND gate.  This circuit has actually been created in vivo.  from http://www.kurzweilai.net/the-most-complex-synthetic-biology-circuit-yet

This is a 4-input AND gate. This circuit has actually been created in vivo. from http://www.kurzweilai.net/the-most-complex-synthetic-biology-circuit-yet

This work was driven by an interest in synthetic biology. Those interested in Insect Genetic Technologies would be well advised to pay attention to the developments in synthetic biology. Much of what synthetic biologists want to do overlaps with the interests of insect molecular geneticists, although synthetic biologists might talk about things slightly differently.  Complex circuit building is a bit beyond what most insect biologists are thinking about at the moment.  Most are primarily concerned with developing platforms that would enable such devices to be constructed in genomes.  Nonetheless, this is a cool paper and it should push the imaginations of insect biologists as they contemplate exploiting genetic technologies for the study of ‘their’ insects.
CRISPR transcriptional repression devices and layered circuits in mammalian cells
Samira Kiani, Jacob Beal, Mohammad R Ebrahimkhani, Jin Huh, Richard N Hall, Zhen Xie, Yinqing Li & Ron Weiss
Nature Methods 11, 723–726 (2014)
doi:10.1038/nmeth.2969

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