In my experiment, I activate a creER mouseline using tamoxifen. The mouse is firstly injected with a cre-dependent virus in the brain, then after several days, tamoxifen is injected i.p. to activate creER.
My questions are:
1. How many days after the virus injection should I inject tamoxifen to activate creER?
2. If I inject tamoxifen for 5 consecutive days, how long can the virus-labeled cells be activated for? My experiment needs long-term monitoring for at least 4 weeks.
Thanks!
Why are you using tamoxifen-inducible Cre-recombinase in your virus? Why not use the constitutive Cre virus? It will eliminate the Tamoxifen step from your experiment.
If you can't change the virus, use Gt(ROSA)26Sor tm14(CAG-tdTomato)Hze /J mice. After tamoxifen injection, you can see your Cre-recombinase infected cells will have red fluorescence and allow you to track your infection efficiency, which might be the biggest challenge of your approach.
Regarding your question in more general terms, Cre recombination is permanent. The part of the DNA in the cells is removed. However, suppose recombined cells are regularly rotated, i.e., macrophages. In that case, new cells will not have the recombination unless you inject tamoxifen again or your Cre affects the cellular source, i.e., bone marrow progenitors. In the brain, most cells are either permanent, i.e., neurons, or at the very least proliferate from recombined cells, retaining the recombination, i.e., microglia or astrocytes.
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