hi,
I am generating a loxp-Cre animal line. However, in order to keep my Cre mice colony going I want to reach the homozygous line so there will no need of PCRs.
In Jackson labs they warn you about the toxicity of Cre expressing activity when the mouse is homozygous, however I understand that until administration of tamoxifen, there should be no risk for them.
What are your thoughts about it?
Thanks!
David
Dear David, here are some reports to have in mind when deciding the use of cre-driver, specially for some drivers widely used like the nestin-cre.
http://www.nature.com/ncomms/journal/v3/n11/full/ncomms2186.html
http://www.sciencedirect.com/science/article/pii/S155041311300209X
Hope it helps
Hi David,
in general we don't find particular problems having Cre lines in homozygosity, even in heterozygosity you do have a lot of Cre around, so toxicity is not a major issue. If one is worried for possible unwanted recombination events, well these would occur also in heterozygosity, but with an estrogen regulated Cre, there should be no problem at all...
The only problem is how the Cre line is designed: if it is a knock-in in a gene whose ko is lethal it will just be impossible to keep it in homozygosity. Often the gene in which the Cre is knocked-in might not be lethal when knocked-out, but affect health, life expectation, behaviour, fertility of the mouse, so it would be better to keep it in heterozygosity.
In general, Rosa26 knock-in Cre lines and transgenic Cre lines can be kept in homozygosity. Knock-in lines is usually better to keep in heterozygosity.
Hi David,
I'd say get enough heterozygotes to establish the colony and try to get homozygotes then.
We bought one homozygous male and one homozygous female of a Cre-ER strain from JAX. JAX says this strain is viable and fertile as homozygotes. After couple months we could not get progeny from breeding these two mice. Female was pregnant once but pups were lost (I missed the birth and don't know what happened exactly).
The same homozygous male bred well with wild type females (C57BL/6J) and we got heterozygous progeny. I don't mind genotyping but prefer to use homozygous parents so I'll set up the same homozygous male with hetetozygous progeny.
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