When the lab of遠照 Shinya Yamanaka re媽紙vealed that vir新你al introduction of Oct3/4, Sox2,和請 Klf4 and c-Myc 站好(OSKM) into adult skin cell暗我s could transform them匠木 into induced pluripotent stem cell請廠s (iPSCs), the wo明草rld quickly took notice 廠放at the prospect of using 畫文iPSC-based-therapies to potentially tre制美at human disease [1-3]. A一志lthough cell-based t拿用herapies have not 綠民lived up to the initial hy照秒pe, nuclear somatic reprogramming r一相emains an invaluable tool fo遠也r modelling human新件 development 月中;and disease [4].金西

It was previously shown that re玩中programming of fibr員中oblasts with the tra站懂nscription factors G在雪ata3, Eomes, Tfap2c, and家地 Myc (GETM) [5] or Ets2 [6匠票] leads to the generation 理放of functional induced trophobl低科ast stem cells (i弟懂TSCs). iTSCs, together with iPSCs an說著d induced XEN e音都xtraembryonic endoderm stem cell秒土s (iXENs) are the in vitro土筆 equivalent cell types of 樂照the blastocyst (the inn事作er cell mass (ICM), primitive endoderm 黃木(PrE) and trophectoderm (TE)). An 匠區exhaustive series of experime近在nts from Benchetrit et al鐘商. have now gone one step 這下further and shown t視海hat a specific combination of facto小場rs, termed GETMS (GETM明雪 together with Esrrb), can dir筆少ectly reprogram fibroblast兵白s into iTSCs, iPSCs and iXENs [7]玩門.

Using a reporter k學視nockin mouse mode匠劇l referred to as BYKE, wh腦關ich marks PSCs and TSCs by南得 Nanog-2A-EGFP a下海nd Elf5-2A-EYFP-NLS re務他spectively, MEFs were isolat厭照ed and reprogrammed into either笑術 iPSCs (Oct4, Sox2,機志 Klf4 and Myc: OS技雨KM) or iTSCs by GETM using lent國弟ivirus transduction. Screening of a窗知 plethora of factors expressed at e玩員arly developmental 個能stages revealed that Esrrb, 鐘技in combination with GETM, is abl大雪e to shift TSC to an PSC fate. Re見喝programming with GETMS (GE紅師TM+Esrrb) under different cu能北lture condition大筆s revealed that these 5 trans體風genes can overcome the lineage 多紅barrier between文跳 embryonic and extra-embryonic c能兵ells to induce iPSC 生師and iTSC lineages. Additional用雪ly, in a secondary MEF sys農工tem (GETMS reprogrammed iPSCs inject森作ed into blastocysts to 小制derive secondary MEFs) allo為女wing the isolati飛時on of lines expres了男sing different stoichiometries 的校of GETMS, further addition of Esrrb an話姐d Eomes induced an iPSC and iTSC fat子校e, respectively. This and transduc物視tion of secondary MEFs under different 草市culture conditions suggested that t事朋he levels of Esrrb 化刀or Eomes dictate the iPSC or iTSC 說就fate during GETMS reprogramming.民愛

To functionally test GETMS-derived 開街cells, GETMS-tdTomato-expressi員歌ng iPSCs and GETMS-EGFP expressing i從務TSCs were injected into blastocysts and話還 whole-transcripto坐什me analysis compared to ESCs and bl裡兵astocyst-derived TSCs (bdTSC) wa明討s carried out. Th微農is revealed that GETMS-iPSCs and -iTS船低Cs can contribute to embryo a的亮nd placenta development. Last玩校ly, again comparing GETMS-iPSCs中森 and -iTSCs to MEF, ESC, iPS行業C, and bdTSC controls at earl影制y time points, RNA短金-Seq and ATAC-Seq suggested照話 GETMS, like OSKM, target an北喝d induce chromatin changes at s做做pecific embryogenic loci. Intere喝市stingly, by compari計雪ng GTMS and GETMS, a role for Esrrb w鐵志as proposed in inducing a ‘XEN-如頻like’ signature where isolat呢筆ed GETMS-iXENs consistently expressed h外如igher levels of Oct4 and Sall4. Pre銀上vious work has shown 筆請that a XEN-like state occurs during西電 reprogramming prio長但r to induction of pluripotency刀微 [8&9].

In summary, this work highlights that 鐵制a specific combination 男北of factors is capable of produc多暗ing the in vitro equi頻線valent of the thre了河e blastocyst cell types and 話術that the spatial and temporal expres的科sion of Esrrb and Eomes m公吃ay be key to determining農體 embryonic cell fate at the earli下業est time point.

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References

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2. Takahashi, K. et al.&nb習少sp;Induction of Pluripotent 知長Stem Cells from Adult Human Fibroblasts們視 by Defined Factors. Cell 131, (2007)雪家.
3. Yu, J. et al. Induced Pluripotent Stem Cell Lines D答鄉erived from Human Somatic C問筆ells. Science 318, (2007).
4. Xu, J. et al. Direct Lineage Reprogramming: Strat綠房egies, Mechanisms, and Applications. Cell Stem Cell,海睡 16, (2015).
5. Benchetrit, H. et al子歌. Extensive Nuclear Reprogramming Un秒樹derlies Lineage Conversi分外on into Functional Trophoblast 大技Stem-like Cells. Cell Stem Cell, 17拿唱, (2015).
6. Kubaczka, C. et al. Direct Induction of Trophoblast 裡算Stem Cells from Murine F學木ibroblasts. Cell Stem Cell, 17, (2015).
7. Benchetrit, H. et al. Direct Induction of t音人he Three Pre-implantation Blas吃玩tocyst Cell Types from Fibroblasts. Cell Stem Cell, 25, (2019).
8. Zhao, Y. et al. A XEN-like State Bridges Somatic音森 Cells to Pluripotency during Chemic有票al Reprogramming. Cell, 163, (2015).
9. Li, X. et al. Direct Reprogramm愛術ing of Fibroblasts via 大長a Chemically Induced 快說XEN-like State. Cell Stem Cell, 21, (2017).