Hi,
Can two genes repress each other's expression?. For example, Gene A inhibits Gene B, Gene B inhibits Gene A. Gene A is a transcription factor goes and binds to the promoter of Gene B and inhibits Gene B expression. Similarly, gene B is a transcription factor, inhibits Gene A expression. So, both Gene A and Gene B are not expressed. Is this mechanism biologically plausible?
Thanks
Yes. This is called a double negative feedback loop. In situations where the inhibition is cooperative (that is, for a doubling in the level of one gene, the level of the other gene more than halves), this circuit forms a bi-stable switch. In a bistable system, only one of the genes can be expressed at once, and which one it is depends on the history of the system (technically, the system has a hysteresis).
Interesting, given how useful they are, such circuits are unrepresented in transcription regulatory networks.
Underrepresented in the networks people have inferred or constructed. Hidden phenomena are hidden.
Perhaps, but their might be other reasons. The requirement for a really good hill coefficient on the repression to properly function as a bistable swtich is difficult to evolve, and without that, you just kind of get an averaging of the expression of the two. However, double negative feedback is over-represented when we talk about a TF and miRNA. One can show that this is because miRNA regulation is inherently non-linear, and so the cooperativity is built in, and thus easier to evolve.
