Reproduction Abstracts

Direct reprogramming of somatic cells to pluripotent stem cells entails the obliteration of somatic cell memory and the reestablishment of epigenetic events. Induced pluripotent stem (iPS) cells have been created by reprogramming somatic cells through the transduction of reprogramming factors. During cell reprogramming, female somatic cells must overcome at least one more barrier to enter a pluripotent state compared to male somatic cells, that is, the reactivation of inactive X chromosome (Xi). To verify this phenomenon, we investigated whether the sex of somatic cells affects the efficiency of reprogramming, differentiation potential, and post-transcriptional process of Xist RNA after reprogramming. There were no differences between male and female iPS cells in the reprogramming efficiency, and in their differentiation potential in-vivo. However, the reactivation of Xi was determined to be a slower process than that of pluripotency-related genes; more than 90% of iPS cells did not complete the reactivation of Xi until 30 day post-infection. Next, we investigated the post-transcriptional processing of Xist RNA, and found that male embryonic stem (ES) cells expressed only the Xist long-isoform,while female ES cells expressed both the Xist long- and short-isoforms.This finding was also observed in iPS cells; male iPS cells only expressed the Xist long-isoform, and female iPS cells expressed the two different Xist isoforms. Based on these findings, we determined that the direct reprogramming of somatic cellsby the transduction of transcription factors results in slow reactivation of Xi, but leads to thecorrect post-transcriptional reprogramming.