Rat-derived feeder cells immortalized by expression of mutant CDK4, cyclin D, and telomerase can support stem cell growth.

The maintenance of stem cells often requires the support of feeder cells. Primary mouse embryonic fibroblasts (MEFs) have traditionally been used as feeder cells, and although these MEF-derived feeder cells have exhibited a reasonable performance, they require repeated cell isolation, since MEFs cannot expand indefinitely. To overcome this limitation, immortalized cells, such as STO cells, have been used. However, one major disadvantage is that previously reported immortalized cells can only support stem cell cultures for a relatively short period, typically 4 to 7 days. In this study, we found that our newly established rat-derived fibroblasts immortalized by the expression of mutant cyclin-dependent kinase 4, cyclin D, and telomerase reverse transcriptase, can function as feeder cells for relatively long cell culture periods of approximately 14 days. The rat-derived immortalized cells developed in this study should be a useful source of feeder cells to support stem cell research.