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In the modern genetically modified animal models, there are not only constitutive mutations which start producing proteins already in the embryo, but also mutations which can be turned on later. I've seen the terms "conditional activation" and "inducible activation" used, especially in the context of Cre-Lox recombination.

Are they used interchangeably, or is there a difference? If they are different, what is the difference?

If I'm looking at a mouse name, like K-Ras+/G12V;Elas-tTA/tetO-Cre;p16Ink4a/19Arflox/lox, how can I recognize which of the two it is?

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  • $\begingroup$ I think that there is a slight distinction. Conditional activation of Cre-Lox can occur simply when Cre is expressed. It could be that you have the Cre gene under the control of a liver promoter, so the recombination will only take place in liver cells. Inducible activation usually means that you add something to the system to induce the recombination event. So if you feed the animals Tamoxifen or G418, then the addition of that chemical will turn on Cre expression leading to recombination. This is probably used when the recombination would be developmentally lethal. $\endgroup$ – AMR Nov 7 '15 at 13:32
  • $\begingroup$ I guess you could say that inducible activation is a subset of conditional activation. $\endgroup$ – AMR Nov 7 '15 at 13:33
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In my opinion the terms inducible and conditional are synonyms. Together with the term constitutive they refer to how transcription takes place, that is, the second phase in the central dogma that states that genetic information is propagated from replication to transcription to translation. The proteins that are produced during translation by ribosomes can have a feedback effect on replication and transcription.

When proteins bind to the promoter region of genes, they can induce or inhibit transcription. If a gene is preceded by a promoter region that always promotes transcription, it is said that the gene has a constitutive promoter. If the gene is transcribed conditionally, it may refer to proteins having to bind to the promoter region so that transcription can take place. There could be inverse situations and I believe the Cre/Lox technology is an example of such a situation.

Take the following as an example. A gene could be lethal meaning that if the protein it encodes is expressed it will kill the cell. It could have a promoter that promotes expression if a protein with an inhibitory effect is not bound to the promoter. Suppose I have these cells in a culture plate and I add some compound to the culture plate. The compound diffuses into the cells and binds to the inhibitory protein that is bound to the promoter region. With this binding of the compound to the protein that is in turn bound to the promoter region, the protein loses its ability to bind to the promoter region and inhibition of transcription is uplifted. Transcription then continues and expression of the lethal protein takes place after which the cell dies.

This could be used in practice as follow: if you were selling seeds to farmers, you would want them to buy seeds next year again, so you want the plant not to be able to produce viable seeds.

Coming back to your question, if you want to know more about the mice in question, you should contact the breeder as nomenclatures differ. See this article on interpreting mouse genetic nomenclature:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3039125/

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    $\begingroup$ It seems that your third paragraph is describing inducible transcription, but is not identified as such. Also while inducible transcription is inherently conditional, conditional transcription need not be inducible, in the sense that the transcription can occur in a given cell type without the addition of an inducer molecule. One need only place the gene under the control of a tissue specific promoter (in recombinant technology) or a gene need only be under the control of that promoter to drive transcription conditionally only in that cell type, with no other action (induction) needed. $\endgroup$ – AMR Nov 8 '15 at 12:20

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