The Differentiation Potency of Trophoblast Stem Cells from Mouse Androgenetic Embryos

Efficient Reprogramming of Mouse Embryonic Stem Cells into Trophoblast Stem-like Cells via Lats Kinase Inhibition

Mouse zygotes undergo multiple rounds of cell division, resulting in the formation of preimplantation blastocysts comprising three lineages: trophectoderm (TE), epiblast (EPI), and primitive endoderm (PrE). Cell fate determination plays a crucial role in establishing a healthy pregnancy. The initial separation of lineages gives rise to TE and inner cell mass (ICM), from which trophoblast stem cells (TSC) and embryonic stem cells (ESC) can be derived in vitro. Studying lineage differentiation is greatly facilitated by the clear functional distinction between TSC and ESC. However, transitioning between these two types of cells naturally poses challenges. In this study, we demonstrate that inhibiting LATS kinase promotes the conversion of ICM to TE and also effectively reprograms ESC into stable, self-renewing TS-like cells (TSLC). Compared to TSC, TSLC exhibits similar molecular properties, including the high expression of marker genes such as Cdx2, Eomes, and Tfap2c, as well as hypomethylation of their promoters. Importantly, TSLC not only displays the ability to differentiate into mature trophoblast cells in vitro but also participates in placenta formation in vivo. These findings highlight the efficient reprogramming of ESCs into TSLCs using a small molecular inducer, which provides a new reference for understanding the regulatory network between ESCs and TSCs.

Dynamic Changes of Gene Expression in Mouse Mural Trophectoderm Regulated by Cdx2 During Implantation

Implantation of the blastocyst into the uterus is a specific and essential process for mammalian embryonic development. In mice, implantation is initiated from the mural trophectoderm of the blastocyst and the mTE controls implantation progression by acquiring the ability to attach and invade into the endometrium while differentiating into primary trophoblast giant cells. Nevertheless, it remains largely unclear when and how the mTE differentiates and acquires this ability during implantation. Here, by RNA sequencing analysis with the pre- and peri-implantation mTE, we show that the mTE undergoes stage-specific and dynamic changes of gene expression during implantation. We also reveal that the mTE begins down-regulating Cdx2 and up-regulating differentiation marker genes during the peri-implantation stage. In addition, using trophectoderm (TE) -specific lentiviral vector-mediated gene transduction, we demonstrate that TE-specific Cdx2 overexpression represses differentiation of the mTE into the primary trophoblast giant cells. Moreover, we reveal that TE-specific Cdx2 overexpression also represses the up-regulation of cell adhesion- and migration-related genes, including Slc6a14, Slc16a3, Itga7, Itgav and Itgb3, which are known to regulate migration of trophectoderm cells. In particular, the expression of Itgb3, an integrin subunit gene, exhibits high inverse correlation with that of Cdx2 in the TE. Reflecting the down-regulation of the genes for TE migration, TE-specific Cdx2 overexpression causes suppression of the blastocyst outgrowth in vitro and abnormal progression of implantation in vivo. Thus, our results specify the time-course changes of global gene expression in the mTE during implantation and uncover the significance of Cdx2 down-regulation for implantation progression.

CDX2 downregulation in mouse mural trophectoderm during peri-implantation is heteronomous, dependent on the YAP-TEAD pathway and controlled by estrogen-induced factors

Purpose

To investigate the transition of CDX2 expression patterns in mouse trophectoderm (TE) and its regulatory mechanisms during implantation.

Methods

Mouse E3.5-4.5 blastocysts were used to immunostain CDX2, YAP, TEAD4, and ESRRB. Endogenous estrogen signaling was perturbed by administrating estrogen receptor antagonist ICI 182,780 or ovariectomy followed by administration of progesterone and β-estradiol to elucidate the relationship between the transition of CDX2 expression patterns and ovarian estrogen-dependent change in the uterine environment.

Results

CDX2 expression was gradually downregulated in the mural TE from E4.0 in vivo, whereas CDX2 downregulation was not observed in blastocysts cultured in KSOM. Fetal bovine serum (FBS) supplementation in KSOM induced CDX2 downregulation independently of blastocyst attachment to dishes. CDX2 downregulation in the mural TE was repressed by administration of ICI 182,780 or by ovariectomy, and administration of β-estradiol into ovariectomized mice retriggered CDX2 downregulation. Furthermore, Cdx2 expression in the mural TE might be controlled by the YAP-TEAD pathway.

Conclusions

CDX2 downregulation was induced heteronomously in the mural TE from E4.0 by uterus-derived factors, the secretion of which was stimulated by ovarian estrogen.

Progesterone depletion results in Lamin B1 loss and induction of cell death in mouse trophoblast giant cells

Trophoblast giant cells (TGCs), a mouse trophoblast subtype, have large amounts of cytoplasm and high ploidy levels via endocycles. The diverse functions and gene expression profiles of TGCs have been studied well, but their nuclear structures remain unknown. In this study, we focus on Lamin B1, a nuclear lamina, and clarify its expression dynamics, regulation and roles in TGC functions. TGCs that differentiated from trophoblast stem cells were used. From days 0 to 9 after differentiation, the number of TGCs gradually increased, but the amount of LMNB1 peaked at day 3 and then slightly decreased. An immunostaining experiment showed that LMNB1-depleted TGCs increased after day 6 of differentiation. These LMNB1-depleted TGCs diffused peripheral localization of the heterochromatin marker H3K9me2 in the nuclei. However, LMINB1-knock down was not affected TGCs specific gene expression. We found that the death of TGCs also increased after day 6 of differentiation. Moreover, Lamin B1 loss and the cell death in TGCs were protected by 10-6 M progesterone. Our results conclude that progesterone protects against Lamin B1 loss and prolongs the life and function of TGCs.

Loss of p57KIP2 expression confers resistance to contact inhibition in human androgenetic trophoblast stem cells

Complete hydatidiform moles (CHMs) develop from androgenetic conceptuses and are characterized by enhanced proliferation of trophoblast cells and a significantly higher risk of trophoblast tumors. Loss of the maternal genome and duplication of the paternal genome are considered to be responsible for the phenotype, but the detailed mechanism remains unclear. Here, we report the derivation of trophoblast stem (TS) cells from CHMs. These cells have reduced sensitivity to contact inhibition of cell proliferation and exhibit aberrant expression of imprinted genes, which are expressed from only 1 parental allele. We also reveal that the maternally expressed imprinted gene p57^KIP2 would be responsible for the enhanced proliferation of CHM-derived TS cells. Our findings provide an insight into the pathogenesis of CHMs.

A complete hydatidiform mole (CHM) is androgenetic in origin and characterized by enhanced trophoblastic proliferation and the absence of fetal tissue. In 15 to 20% of cases, CHMs are followed by malignant gestational trophoblastic neoplasms including choriocarcinoma. Aberrant genomic imprinting may be responsible for trophoblast hypertrophy in CHMs, but the detailed mechanisms are still elusive, partly due to the lack of suitable animal or in vitro models. We recently developed a culture system of human trophoblast stem (TS) cells. In this study, we apply this system to CHMs for a better understanding of their molecular pathology. CHM-derived TS cells, designated as TS^mole cells, are morphologically similar to biparental TS (TS^bip) cells and express TS-specific markers such as GATA3, KRT7, and TFAP2C. Interestingly, TS^mole cells have a growth advantage over TS^bip cells only after they reach confluence. We found that p57^KIP2, a maternally expressed gene encoding a cyclin-dependent kinase inhibitor, is strongly induced by increased cell density in TS^bip cells, but not in TS^mole cells. Knockout and overexpression studies suggest that loss of p57^KIP2 expression would be the major cause of the reduced sensitivity to contact inhibition in CHMs. Our findings shed light on the molecular mechanism underlying the pathogenesis of CHMs and could have broad implications in tumorigenesis beyond CHMs because silencing of p57^KIP2 is frequently observed in a variety of human tumors.