Pluripotent cells are at the origin of definitive structures of the developing fetus. Understanding pluripotency is therefore a major goal of cell fate and early development fields of research, as well as regenerative medicine and in vitro fertilization medical fields. Pluripotency exists in 2 major states in mammals: naive pluripotency and primed pluripotency (Tesar, 2016). Pre-implantation epiblast cells, corresponding to the naive sate of pluripotency, are the first pluripotent cells that emerge within embryos (day 5 in human) and represent the ground state of pluripotency. Post-implantation epiblast cells, representing the primed state of pluripotency, are epigenetically preparing for differentiation. Human embryonic stem cell lines (hESC) derived in 1998 (Thomson et al., 1998) and human induced pluripotent stem cells (hiPSC) discovered in 2007 (Takahashi et al., 2007; Yu et al., 2007) are in a primed state of pluripotency. Recent advances in single cell transcriptomic analysis of human embryos have highlighted major differences between the epiblast cells of the human preimplantation embryos that reside in the naive state of pluripotency and the human embryonic stem cell lines used in labs (Blakeley et al., 2015; Petropoulos et al., 2016; Yan et al., 2013). Therefore, laboratories around the world are actively attempting to establish tissue culture conditions that support the growth of naive pluripotent stem cells in culture, closely related to human epiblast cells from pre-implantation embryos.
The main approach to generate human naive PSC is to reset primed hESC to the naive state. While multiple groups have published media allowing to reset cells, the most successful strategy relies on overexpression of NANOG and KLF2 until naive cells are obtained. Naive cells can then self-renew in a specific media upon transgene withdrawal (Takashima et al., 2014; Theunissen et al., 2014). In 2016, several groups reported the derivation of human naive embryonic stem cells (hNESC) directly into naive media: those are the first naive cell lines generated without passing through a primed intermediate state (Guo et al., 2016; Pastor et al., 2016).
Diverse naive cell lines have been generated, raising new questions how naive pluripotency is established and regulated. Therefore, we need to established new model systems to investigate these important questions in stem cell biology. The current gold standard model is human embryos. However, they have limited experimental options and have ethical restrictions. Here, we propose to complement human embryos experiments with specific human naive pluripotent stem cells lines as powerful models to understand regulation and establishment of pluripotency.
We aim to characterize specific factors regulating the establishment of pluripotency using an innovative naive reprogramming method and validating our results in human preimplantation embryos.
Ethical aspects: The Agence de la Biomédecine (French medical ethical board) has approved the proposed research under approval numbers RE13-004, RE13-010 and RE15-018.
- Blakeley, P., et al. (2015). Defining the three cell lineages of the human blastocyst by single-cell RNA-seq. Development.
- Guo, G., et al. (2016). Naive Pluripotent Stem Cells Derived Directly from Isolated Cells of the Human Inner Cell Mass. Stem Cell Reports.
- Pastor, W.A., et al. Cell stem cell 18, 323-329.
- Petropoulos, S., et al. (2016). Single-Cell RNA-Seq Reveals Lineage and X Chromosome Dynamics in Human Preimplantation Embryos. Cell.
- Takahashi, K., et al. (2007). Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell 131, 861-872.
- Takashima, Y., et al. (2014). Resetting transcription factor control circuitry toward ground-state pluripotency in human. Cell 158, 1254-1269.
- Tesar, P.J. (2016). Snapshots of Pluripotency. Stem Cell Reports 6, 163-167.
- Theunissen, Thorold W., et al. (2014). Systematic Identification of Culture Conditions for Induction and Maintenance of Naive Human Pluripotency. Cell stem cell.
- Thomson, J.A., et al (1998). Embryonic stem cell lines derived from human blastocysts. Science 282, 1145-1147.
- Yan, L., et al. (2013). Single-cell RNA-Seq profiling of human preimplantation embryos and embryonic stem cells. Nature structural & molecular biology.
- Yu, J., et al. (2007). Induced pluripotent stem cell lines derived from human somatic cells. Science 318, 1917-1920.