RNA-seq analysis of ES cell populations with different functional potentials in serum/LIF and 2i/LIF, as well as analysis of the transcriptional effect of LIF in ground state (2i) culture conditions.
We report that ES cells cultured in ground state (2i and 2i/LIF) culture conditions are heterogeneous and show heterogeneus expression of extraembryonic markers. Using a highly sensitive reporter for the endoderm marker Hex we can sort Hex high and low populations from either serum/LIF or 2i/LIF and demonstrate that they have different functional properties. Here we explored the transcriptional basis of these functional differences and noted that Hex low (HV-) and Hex high (HV+) populations showed  more distinct expression profiles in 2i/LIF than in serum/LIF. Additionally in 2i/LIF the HV+ population showed an upregulation of extraembryonic markers (such as trophoblast stem cell specific genes) and also imprinted genes compared to the HV- population, which is not observed when these populations are sorted from serum/LIF. We also analysed the transcriptional effect of LIF in 2i by analysing unsorted ES cells cultured in either 2i alone or 2i with LIF. We observed that the addition of LIF led to an upregulation of extraembryonic markers but did not effect the expression of pluripotency genes, other than Klf4. Additionally, the most significantly upregulated genes from 2i/LIF cultured ES cells compared to 2i cultured ES cells showed the greatest correlation to placental tissue when compared to the GNF tissue specific expression database. This analysis, alongside functional experiments, suggested that HV+ ES cells in 2i/LIF corresponded to an extraembryonically primed population of cells and that the addition of LIF supported this population. Overall design: RNA-seq of sorted Hex low and high expressing ES cell populations cultured in serum/LIF or 2i/LIF as well as unsorted ES cells from 2i or 2i/LIF.