Hello everybody!
We have been doing IP injections of Tamoxifen to pregnant Cre-loxP mice, for lineage tracing during development.
We usually make a single injection at E11.5 with a dose of Tamoxifen ranging from 1.5 mg to 3.0 mg (depending on the reporter system), combining it with half-dose of Progesteron to counteract the estrogenic effects of Tamoxifen. The embryos are then collected at E17.5.
Our driver CRE strain is crossed with different reporters, like the Brainbow 2.1 (also called Rosa-Confetti), that we never used before in this lab.
Every time that we inject Tamoxifen in the pregnant Confetti females we either have abortions or high mortality of the mothers, in ratios that are not observed with our other reporter strains in use (nlacZ, tdTomato).
Does anybody use Confetti mice and had the same problem? Is it the concentration of Tamoxifen too high? Are they somehow oversensitive?
Thank you!
Hi Irene,
I had a similar problem when working with pregnant dams in a cre-inducible line that seemed to be more sensitive than others I had used before. It's not the Confetti strain, but my troubleshooting might be of assistance here!
It's important to remember that tamoxifen isn't what actually induces your cre. 4-hydroxytamoxifen is, and it's produced by digestion of tamoxifen within the liver. For stronger induction with less toxicity, I moved to oral gavage rather than IP injection. This way, you optimize for digestion and minimize the amount of undigested tamoxifen that is taken up by the mouse's fat stores or transferred to the embryos.
For gavage, I use 20mg/mL tamoxifen in corn oil fed at 10ul per gram of mouse. I repeat the gavage on 3 consecutive days, being sure to have at least 24 hours between each feeding.
For my pregnant dams, I also omitted the progesterone. It's great to include progesterone with a normal tamoxifen induction to counteract the estrogenic effects of tamoxifen (just as you said!), but I found that I would lose some embryos when giving progesterone.
I hope this helps!
Melissa
- Badges
- Science topic
- Similar topics
- Clinical Pharmacology
- Dosing