The Jackson Laboratory has introduced two new researchtools—JAX Mouse Embryonic Stem Cells (mES) and JAX Mouse Embryonic Fibroblasts(MEFs). JAX mES cells are self-renewing, non-transformed cell lines establishedfrom day 3.5 blastocysts and can differentiate into all three embryonic germlayers: endoderm, ectoderm and mesoderm. JAX mES cells are well-suited for evaluating drug efficacy, regenerativemedicine and gene targeting. JAX MEFs are primary cells with a wide range ofapplications, including toxicology, compound testing and embryonic stem cellgrowth support. Available either irradiated or not, JAX MEFs are isolated fromhigh health status, gold-standard JAX Mice rigorously tested for tissue culturecontaminants, including mycoplasma.