I'm new to MEFs and cell culture in general. I normally go only so far as to make a few primary cell cultures from embryos when and where I need them (and normally chicken not mice). But I did have some mice embryonic fibroblasts in culture from a C57BL6/CD1 background (both wt and knockout MEFs). They went senescent...and then the knockout MEFs started growing again. I guess they've become immortalised? I've expanded them and now have put them through 5 passages up to 100cm2 flasks, so I can freeze them down. They are from a very useful mutant line, which are usually early embryo lethal. So...great this is a very nice thing to happen. But I've got no controls! The control wt culture never became immortalised, so what do I do now? Can I use something like a 3T3 line as a control? Make primary fibroblasts? I'd like to do a microarray asap, so I can compare gene expression to my other mutants. Any ideas? Also does this mean my gene of interest, which was knocked-out could be a tumor-supressor?