I have a homozygous mouse strain expressing Cre recombinase from promoter X (strain X-Cre) and another homozygous mouse strain with a gene flanked by loxP sites (strain Z-LoxP).
How do I obtain a population of mice that is homozygous for the tissue specific KO?
Here is what I think, please correct me if/when I'm mistaken.
Mate the homozygous X-Cre with the homozygous Z-loxP strain. This will generate 100% F1 offspring heterozygous for each mutation, and so heterozygous for gene Z conditional knockout.
At this point you breed the offspring. 25% of the F2 generation will then be homozygous for X-Cre and Z-LoxP. These mice can then be bred to generate a uniform colony.
Is this right? If not, where did I go wrong?
Thanks in advance
If the excised construct is in the brain tissue (let's say) only, because it uses a tissue-specific promoter. How does it pass through germ line to the next generation?
If Yoy want to make GFAPcre and PPARE LOX mouse you have to use homozygus Cre meet with lox after few generation you can get homozygus Cre lox.
From a Mendelian genetics standpoint, you have this correct. The factor that needs to be considered in the scenario you have described is if a homozygous Cre strain is possible. Certain Cre strains are not embryonically viable as the replacement of a gene behind a given reporter with the Cre enzyme is equivalent to creating a genetic knockout of this gene and thus can be embryonically lethal. So, even if it is possible to create homozygous Cre mouse using your promoter of interest, you need to assess if the deletion of the gene behind this promoter will affect the function of your cells of interest and would affect the viability of your model. A possible work around for this would be creating a Cre line that has the Cre enzyme inserted after the gene of interest and separated by an IRES site. So, it would look like Promoter-Gene-IRES-Cre.