In recent years, haploid stem cells derived from mammals have shown significant advantages in screening key functional genes due to single-genome and self-renewal features. Research Fellow Shuai Ling from the State Key Laboratory of Medicinal Chemical Biology, College of Pharmacy at Nankai University has been working in the field of haploid stem cell and genetic screening research for more than ten years. He has successively developed various types of lineage-specific haploid stem cells, including haploid embryonic stem cells, haploid neural stem cells, and haploid trophoblast stem cells, for 4 species - mice, rats, monkeys, and humans. He also fully revealed unknown functional genes related to toxic drug targets and differentiation and dedifferentiation.

Recently, Shuai Ling’s team made a discovery on the mechanism underlying ESC-to-TSC transition (ESC: ICM-derived embryonic stem cell, TSC: TE-derived trophoblast stem cell). Through the knockout (KO) of Dyrk1a, which has the highest mutation frequency among candidate genes, can promote ESCs to obtain totipotency, thereby letting them differentiate into the trophoblast lineage.

By injection into embryo, Dyrk1a-KO ESCs could contribute to fetus, placenta, and yolk sac in vivo in chimera production experiment.

The first cell fate decision in mice occurs at the time between the 4-cell embryo stage and the 8-cell embryo stage, which leads to two different cell lineages. In this period, identical blastomeres segregate to the inner cell mass (ICM) (which further develops into yolk sac and fetus) and trophectoderm (TE) (which further develops into placenta). ICM and TE are unable to naturally transition to the other in murine species. The restriction mechanism is unknown. ICM-derived embryonic stem cells (ESCs) and TE-derived trophoblast stem cells (TSCs) are excellent platforms to study the relationships and differences between ICM and TE in vitro, because they retain the characteristics of the source cells in multiple aspects.

Shuai Ling’s team took mouse haploid ESCs as an important tool and performed a high-throughput genetic screening, and found the key genes regulating ESC-TSC transition. The top 2 candidate genes (Catip and Dyrk1a) were chosen from numerous candidate genes for validation experiments, which could efficiently promote the conversion from ESCs to TSCs in mice.

Totipotent cells only exist in early-developing embryos, and there are no stable totipotent cell lines in vitro. How to obtain totipotent stem cell lines has been a research hotspot in the fields of developmental biology and cell biology. This study performed cluster analysis on Dyrk1a-KO ESCs and several totipotent cells reported in recent years. The results showed that this cell line is very similar to TBLCs from Du Peng’s team of Peking University (Shen et al, Cell, 2021) at the transcriptome level, but quite different from ciTotiSCs in Ding Sheng’s team of Tsinghua University (Hu et al, Nature, 2022) and TLSCs in Wang Jichang’s team of Sun Yat-sen University (Yang et al, Cell Stem Cell, 2022). Finally, Shuai Ling’s team validated the totipotency of Dyrk1a-KO ESCs by chimeric experiments and the formation of blastocyst-like structures. The results showed that this cell line can not only contribute to the fetus, placenta, and yolk sac, but also efficiently forms blastoids that are very similar to the blastocyst in vitro, indicating that KO of Dyrk1a activates a totipotent-like state.

Shuai Ling stated that this study not only revealed a large number of key genes regulating ESCs to TSCs transition in the mice, but also provides new ideas for obtaining the totipotent cells. This study also could promot the development of developmental biology.

On December 20, this paper was published online in the famous international academic journal - Science Advances. Research Fellow Shuai Ling and Dr. Gao Qian from the State Key Laboratory of Medicinal Chemical Biology, College of Pharmacy at Nankai University, and Professor Wu Xudong from Tianjin Medical University are co-corresponding authors.

Paper link:

https://www.science.org/doi/10.1126/sciadv.adi5683

（Edited and translated by Nankai News Team.)