Does anyone know of an example of a gene that is essential to mouse embryo fibroblasts (MEFs), in that cells die when treated with Cre recombinase that leads to deletion of the gene. But it is not essential in mice, as expression of Cre using an ubiquitous promoter resulted in deletion of the gene but the animals have no discernible phenotypes?
Sorry, but I never experienced this situation.
Honestly MEFs are our "lifeboat" when the mouse phenotype is late embryonic lethal: if embryos reach E13.5-14.5 we can make MEFs and study in vitro the gene function, since MEFs will survive despite the lethal mouse phenotype...
If MEFs can't survive in vitro I doubt a mouse will have no phenotype... connective tissue is too important for a multicellular organism.
But, I may be missing something, maybe somebody will be able to help!
Hello Richard, this is a pretty difficult question..!
In our experience MEFs are our "life boat" when a phenotype is (late) embryonic lethal. So, it actually works the other way round, MEFs can survive even if the animal does not. We never experienced what you ask, that mutant MEFs cannot survive but the ko animal has no or little phenotype. Which makes some sense... how can a complex organism survive without connective tissue? But of course I can only rely on a limited number of gene inactivations...
I agree that this is a confusing and unexpected situation and I have not seen it published from any other group. Most people I have spoken with are mouse geneticists who don't often use MEFs, or cell biologists who don't think much about mice phenotypes. If I were to have to guess the difference may be that in the animal there may be compensatory mechanisms available that cannot happen in MEFs. But I am definitely guessing with no data!
Hi Richard, sorry for the double message, something didn't work the first time, it looked like my first one didn't load, even the day after...!
Anyway, I see your point and you might actually be quite right! I'm thinking now that we have in the lab something that goes in your direction... It is not among my projects and this is a very public place, so I don't want to go into details, but I'll tell you the point. We have introduced a small deletion into a gene and this somehow affects specifically brain development in the mouse embryo although the protein is ubiquitously expressed, so that at E18.5 the embryo has a perfect body but starting from the hindbrain it becomes a mess. If we make MEFs at E14.5, using only the body of the embryo, we get a very strong phenotype, cells overgrow in size (hypertrophy), go into senescence quickly and don't divide properly... So it's not completely lethal, but for sure a severe phenotype in MEFs, although in the whole embryo there seems to be no phenotype at all, at least concerning fibroblasts, we only see a neuronal phenotype...
I didn't pay too much attention to this (we are kind of used at not comparing cell culture conditions to live animal phenotypes, we use cell culture just to study cell autonomous mechanism...) but I would say it fits with your idea... Still, unfortunately we have no idea why this happens and what function of the protein the deletion has affected!! So from this side I can't be of much help!!
All the best!
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