Generation of embryonic stem cells derived from the inner cell mass of blastocysts of outbred ICR mice.

Embryonic stem cells (ESCs) derived from outbred mice which share several genetic characteristics similar to humans have been requested for developing stem cell-based bioengineering techniques directly applicable to humans. Here, we report the generation of ESCs derived from the inner cell mass of blastocysts retrieved from 9-week-old female outbred ICR mice mated with 9-week-old male outbred ICR mice (ESCs). Similar to those from 129/Ola mouse blastocysts (ESCs), the established ESCs showed inherent characteristics of ESCs except for partial and weak protein expression and activity of alkaline phosphatase. Moreover, ESCs were not originated from embryonic germ cells or pluripotent cells that may co-exist in outbred ICR strain-derived mouse embryonic fibroblasts (MEFs) used for deriving colonies from inner cell mass of outbred ICR mouse blastocysts. Furthermore, instead of outbred MEFs, hybrid MEFs as feeder cells could sufficiently support maintenance of ESC self-renewal. Additionally, ESC-specific characteristics (self-renewal, pluripotency, and chromosomal normality) were observed in ESCs cultured for 40th subpassages (164 days) on MEFs without any alterations. These results confirmed the successful establishment of ESCs derived from outbred ICR mice, and indicated that self-renewal and pluripotency of the established ESCs could be maintained on MEFs in culture.