Comparison of reprogramming ability of mouse ES and iPS cells measured by somatic cell fusion.

The ectopic expression of the key transcription factors Oct4, Sox2, c-Myc, and Klf-4 have been shown to reprogram somatic cells to a pluripotent state. In turn these induced pluripotent stem (iPS) cells, like embryonic stem (ES) cells, have been shown to be able to reprogram somatic cells by cell fusion. In this study we compare the differences and similarities between ES and iPS cells measured by somatic cell fusion to somatic cells harboring an Oct4-GFP transgene. We found that iPS cells were just as potent as ES cells at reprogramming the somatic genome as measured by Oct4-GFP reactivation. The resulting ES-somatic and iPS-somatic cell hybrids were characterized for expression of key pluripotency genes, immunostaining for Oct4, SSEA-1, and the ability to differentiate into cell types representative of the three germ layers. In addition to restoring pluripotency to the somatic genome following cell fusion, the telomere maintenance mechanisms of both the ES and iPS cells were found to be dominant in the resulting ES-somatic and iPS-somatic cell hybrids, resulting in the lengthening of the somatic telomeres following cellular reprogramming. Therefore this study supports the view that iPS cells can be virtually indistinguishable from ES cells, even with regard to their reprogramming ability.