Hi, everyone. I am working on using inducible CreERT2 system to knock out (down) target gene. I did extensive experiments to validate it. I found 2.2 mg/per adult mouse with 4 injections could remove our target gene by 70~80% efficiency (in our mouse model, we use tomato reporter, and all of the knockout efficiency refers to that in the tomato positive cells), while 2.2 mg/per mouse with 1 injection cannot remove the target gene. So I am considering to increase the dosage of tamoxifen for one injection, hoping the knockout efficiency could be over 60%. I am wondering who know how much tamoxifen is maximal safe dosage. And another question is how much knockout efficiency is in your mouse. Very appreciate!
I am not sure why you want to just do a single injection with high dose of Tamoxifen. To get the best knockdown, an implanted tablet works more efficiently. As for injections, we normally do daily for 5 days in a row. There is a subtantial weight loss by the end, but the effiency is around 90%.
Hi, Zhang, thanks for your reply. I want to do cell lineage tracing. I am wondering how many days after last tamoxifen injection you terminate mice to check knockout efficiency. Additionally, how much maximal tamoxifen dosage did you use and the mice can still tolerate that. Thanks for your help!
We used 1mg/kg tamoxifen (i.p.) daily and mice are doing ok. We checked cre expression the day after the last injection but did experiments 10 more days later to allow mice to recover from acute toxicity caused by tamoxifen. With in vitro experiments, you don't need to wait that long.
Dear Huajun, you can do e.g. in eight weeks old mice i.p. injections with 1 mg of tamoxifen either once or twice per day for five consecutive days. see this paper: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1955451/
we usually wait 1-2 weeks after last Tam dose, this depends on the gene you want to detect (luciferase might no accumulate more after some days, for GFP there will be more expression after a while.
The 2 mg/day is already a high dose to my view and I would not increase it.
I have a technical question. Do you use sigma aldrich tamoxifen? if anyone uses it. I want to prepare the tamoxifen dose for injection. I will dissolve it in corn oil. The label on the bottle says 1G, do you use the whole weight of the powder in the bottle or you measure the weight you require? as I tried to do so but I am afraid during handling the powder that I might lose some with weighing. Anyways I tried to take 0.5 gm but I became doubtful as the amount left after taking 0.5gm didn't seem to be 0.5gm. I want to make sure if the bottle has 1gm tamoxifen or more. Does anybody can help?
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