Problem
We need more ways of reliably recording state for long periods of time in cells, especially mammalian.
Approach
(this is a pretty old picture so not the most accurate but shows the effect well) scientists believe memory can be stored for a long time partly through proteins in the synpase that oligomerize in response to neural stimulus and self-perpetuate through prion-like behaviour. The oligomers cause the translation of specific mRNA which maintain the long term facilitation of the synapse.
Could we use these self-perpetuating oligomers to store memory for us? It would be a latch rather than a toggle switch because the oligomers are hard to get rid of once they've formed.
the oligomerization is regulated with a number of chemicals- LimK, Tob, PP2A as shown above. Orb2B and Orb2A are the proteins that make up the oligomers. Orb2B is present in large amounts but requires Orb2A to oligomerize, however Orb2A is rarer, and destabilized by PP2A. Orb2A and LimK are produced in response to neural stimulus (like neurotransmitters like tyramine). Orb2A is then stabilized by Tob and LimK, allowing the oligomer to form. We could experiment with adjusting the levels of each of these substances individually while keeping the others stable in order to flip the latch.
We could put the sequences of the oligomerizing proteins (Orb2A and Orb2B) and the regulatory chemicals into mammalian cells and see if we can get the oligomer to form (and test its presence using western blotting/immunoprecipitation)
We could then experiment with changing the sequence of the proteins' RNA binding domains to get it to activate the translation of mRNA and thus the production of proteins that we specify, serving as output. It's unclear if changing the RNA binding domain would impair the oligomerization, although scientists have added sequences encoding a C-terminal GFP tag to the sequence encoding the RBD in Orb2 and found that the function of both GFP and Orb 2 was not impaired.
questions:
What can this be used for?
Uses:
overcome high production costs associated with requiring large quantities of chemical inducer.
- get cells to deliver drugs based on the history of exposure to something eg a toxin
- Track what happens to populations of cells under interesting conditions (every cell that was ever exposed to X or ever produces a certain threshold amount of Y gets an oligomer)
- sequential logic gates like a delayed response AND gate, an OR gate that implements a circuit where output is 1 if either input was ever 1.
What's the mechanism for the oligomer stabilizing the mRNA and getting it to be translated? How do we know it will work? How can we troubleshoot it?