Derivation of Mouse Haploid Trophoblast Stem Cells

Development and application of haploid embryonic stem cells

Haploid cells are a kind of cells with only one set of chromosomes. Compared with traditional diploid cells, haploid cells have unique advantages in gene screening and drug-targeted therapy, due to their phenotype being equal to the genotype. Embryonic stem cells are a kind of cells with strong differentiation potential that can differentiate into various types of cells under specific conditions in vitro. Therefore, haploid embryonic stem cells have the characteristics of both haploid cells and embryonic stem cells, which makes them have significant advantages in many aspects, such as reproductive developmental mechanism research, genetic screening, and drug-targeted therapy. Consequently, establishing haploid embryonic stem cell lines is of great significance. This paper reviews the progress of haploid embryonic stem cell research and briefly discusses the applications of haploid embryonic stem cells.

The transcriptional activator Klf5 recruits p300-mediated H3K27ac for maintaining trophoblast stem cell pluripotency

The effective proliferation and differentiation of trophoblast stem cells (TSCs) is indispensable for the development of the placenta, which is the key to maintaining normal fetal growth during pregnancy. Kruppel-like factor 5 (Klf5) is implicated in the activation of pluripotency gene expression in embryonic stem cells (ESCs), yet its function in TSCs is poorly understood. Here, we showed that Klf5 knockdown resulted in the downregulation of core TSC-specific genes, consequently causing rapid differentiation of TSCs. Consistently, Klf5-depleted embryos lost the ability to establish TSCs in vitro. At the molecular level, Klf5 preferentially occupied the proximal promoter regions and maintained an open chromatin architecture of key TSC-specific genes. Deprivation of Klf5 impaired the enrichment of p300, a major histone acetyl transferase of H3 lysine 27 acetylation (H3K27ac), and further reduced the occupancy of H3K27ac at promoter regions, leading to decreased transcriptional activity of TSC pluripotency genes. Thus, our findings highlight a novel mechanism of Klf5 in regulating the self-renewal and differentiation of TSCs and provide a reference for understanding placental development and improving pregnancy rates.

Dissecting embryonic and extraembryonic lineage crosstalk with stem cell co-culture

Embryogenesis necessitates harmonious coordination between embryonic and extraembryonic tissues. Although stem cells of both embryonic and extraembryonic origins have been generated, they are grown in different culture conditions. In this study, utilizing a unified culture condition that activates the FGF, TGF-β, and WNT pathways, we have successfully derived embryonic stem cells (FTW-ESCs), extraembryonic endoderm stem cells (FTW-XENs), and trophoblast stem cells (FTW-TSCs) from the three foundational tissues of mouse and cynomolgus monkey (Macaca fascicularis) blastocysts. This approach facilitates the co-culture of embryonic and extraembryonic stem cells, revealing a growth inhibition effect exerted by extraembryonic endoderm cells on pluripotent cells, partially through extracellular matrix signaling. Additionally, our cross-species analysis identified both shared and unique transcription factors and pathways regulating FTW-XENs. The embryonic and extraembryonic stem cell co-culture strategy offers promising avenues for developing more faithful embryo models and devising more developmentally pertinent differentiation protocols.

BCL2 is a major regulator of haploidy maintenance in murine embryonic stem cells

Mammalian haploid cells are important resources for forward genetic screening and are important in genetic medicine and drug development. However, the self-diploidization of murine haploid embryonic stem cells (haESCs) during daily culture or differentiation jeopardizes their use in genetic approaches. Here, we show that overexpression (OE) of an antiapoptosis gene, BCL2, in haESCs robustly ensures their haploidy maintenance in various situations, even under strict differentiation in vivo (embryonic 10.5 chimeric fetus or 21-day teratoma). Haploid cell lines of many lineages, including epiblasts, trophectodermal lineages, and neuroectodermal lineages, can be easily derived by the differentiation of BCL2-OE haESCs in vitro. Transcriptome analysis revealed that BCL2-OE activates another regulatory gene, Has2, which is also sufficient for haploidy maintenance. Together, our findings provide an effective and secure strategy to reduce diploidization during differentiation, which will contribute to the generation of haploid cell lines of the desired lineage and related genetic screening.

Transcriptome profiles and chromatin states in mouse androgenetic haploid embryonic stem cells

Haploid embryonic stem cells (haESCs) are derived from the inner cell mass of the haploid blastocyst, containing only one set of chromosomes. Extensive and accurate chromatin remodelling occurs during haESC derivation, but the intrinsic transcriptome profiles and chromatin structure of haESCs have not been fully explored. We profiled the transcriptomes, nucleosome positioning, and key histone modifications of four mouse haESC lines, and compared these profiles with those of other closely-related stem cell lines, MII oocytes, round spermatids, sperm, and mouse embryonic fibroblasts. haESCs had transcriptome profiles closer to those of naïve pluripotent stem cells. Consistent with the one X chromosome in haESCs, Xist was repressed, indicating no X chromosome inactivation. haESCs and ESCs shared a similar global chromatin structure. However, a nucleosome depletion region was identified in 2056 promoters in ESCs, which was absent in haESCs. Furthermore, three characteristic spatial relationships were formed between transcription factor motifs and nucleosomes in both haESCs and ESCs, specifically in the linker region, on the nucleosome central surface, and nucleosome borders. Furthermore, the chromatin state of 4259 enhancers was off in haESCs but active in ESCs. Functional annotation of these enhancers revealed enrichment in regulation of the cell cycle, a predominantly reported mechanism of haESC self-diploidization. Notably, the transcriptome profiles and chromatin structure of haESCs were highly preserved during passaging but different from those of differentiated cell types.

Dissecting embryonic and extra-embryonic lineage crosstalk with stem cell co-culture

Faithful embryogenesis requires precise coordination between embryonic and extraembryonic tissues. Although stem cells from embryonic and extraembryonic origins have been generated for several mammalian species(Bogliotti et al., 2018; Choi et al., 2019; Cui et al., 2019; Evans and Kaufman, 1981; Kunath et al., 2005; Li et al., 2008; Martin, 1981; Okae et al., 2018; Tanaka et al., 1998; Thomson et al., 1998; Vandevoort et al., 2007; Vilarino et al., 2020; Yu et al., 2021b; Zhong et al., 2018), they are grown in different culture conditions with diverse media composition, which makes it difficult to study cross-lineage communication. Here, by using the same culture condition that activates FGF, TGF-β and WNT signaling pathways, we derived stable embryonic stem cells (ESCs), extraembryonic endoderm stem cells (XENs) and trophoblast stem cells (TSCs) from all three founding tissues of mouse and cynomolgus monkey blastocysts. This allowed us to establish embryonic and extraembryonic stem cell co-cultures to dissect lineage crosstalk during early mammalian development. Co-cultures of ESCs and XENs uncovered a conserved and previously unrecognized growth inhibition of pluripotent cells by extraembryonic endoderm cells, which is in part mediated through extracellular matrix signaling. Our study unveils a more universal state of stem cell self-renewal stabilized by activation, as opposed to inhibition, of developmental signaling pathways. The embryonic and extraembryonic stem cell co-culture strategy developed here will open new avenues for creating more faithful embryo models and developing more developmentally relevant differentiation protocols.

Advances in haploid embryonic stem cell research

Haploid embryonic stem cells are embryonic stem cells of a special type. Their nuclei contain one complete set of genetic material, and they are capable of self-renewal and differentiation. The emergence of haploid embryonic stem cells has aided research in functional genomics, genetic imprinting, parthenogenesis, genetic screening, and somatic cell nuclear transfer. This article reviews current issues in haploid stem cell research based on reports published in recent years and assesses the potential applications of these cells in somatic cell nuclear transfer, genome imprinting, and parthenogenesis.

Derivation of human triploid trophoblast stem cells

PURPOSE

Human trophoblast stem cells (hTSCs) are counterparts of the precursor cells of the placenta and are valuable cell models for the study of placental development and the pathogenesis of placental diseases. The aim of this work was to establish a triploid human TSC (hTSC^3PN) derived from the tripronuclear embryos, which are clinically discarded but readily available, for potential applications in basic placental research and disease modeling.

METHODS

Eighteen tripronuclear human zygotes from IVF were collected and cultured for 5-6 days. Five high-quality blastocysts were harvested and were individually cultured in hTSC medium. Finally, two hTSC lines were established after 10 days and could be passaged stably.

RESULTS

The karyotyping analysis showed that hTSC^3PN contained three sets of chromosomes. And the hTSC^3PN exhibited typical features of hTSCs, with the ability to differentiate into two trophoblast lineages: extravillous cytotrophoblasts (EVTs) and syncytiotrophoblasts (STs). In addition, the hTSC^3PN can mimic some vital features of trophoblast, including hormone secretion and invasion. Further studies showed that the proliferation and differentiation of hTSC^3PN were reduced compared with normal hTSCs, which may be related to the disturbed metabolic signaling in hTSC^3PN.

CONCLUSIONS

We established the triploid hTSC lines derived from tripronuclear embryos, which provides a potentially useful research model in vitro to study human placental biology and diseases.

Applications of piggyBac Transposons for Genome Manipulation in Stem Cells

Transposons are mobile genetic elements in the genome. The piggyBac (PB) transposon system is increasingly being used for stem cell research due to its high transposition efficiency and seamless excision capacity. Over the past few decades, forward genetic screens based on PB transposons have been successfully established to identify genes associated with drug resistance and stem cell-related characteristics. Moreover, PB transposon is regarded as a promising gene therapy vector and has been used in some clinically relevant stem cells. Here, we review the recent progress on the basic biology of PB, highlight its applications in current stem cell research, and discuss its advantages and challenges.

High-throughput screening in postimplantation haploid epiblast stem cells reveals Hs3st3b1 as a modulator for reprogramming

Epiblast stem cells (EpiSCs) derived from postimplantation epiblast are pluripotent stem cells, epigenetically distinct from embryonic stem cells (ESCs), which are widely used in reprogramming studies. Recent achieved haploid cell lines in mammalian species open a new era for high-throughput genetic screening, due to their homozygous phenotypes. Here, we report the generation of mouse haploid EpiSCs (haEpiSCs) from postimplantation chimeric embryos at embryonic day 6.5 (E6.5). These cells maintain one set of chromosomes, express EpiSC-specific genes, and have potentials to differentiate into three germ layers. We also develop a massive mutagenesis protocol with haEpiSCs, and subsequently perform reprogramming selection using this genome-wide mutation library. Multiple modules related to various pathways are implicated. The validation experiments prove that knockout of Hst3st3b1 (one of the candidates) can promote reprogramming of EpiSCs to the ground state efficiently. Our results open the feasibility of utilizing haEpiSCs to elucidate fundamental biological processes including cell fate alternations.

The milestone of genetic screening: Mammalian haploid cells

Mammalian haploid cells provide insights into multiple genetics approaches as have been proved by advances in homozygous phenotypes and function as gametes. Recent achievements make ploidy of mammalian haploid cells stable and improve the developmental efficiency of embryos derived from mammalian haploid cells intracytoplasmic microinjection, which promise great potentials for using mammalian haploid cells in forward and reverse genetic screening. In this review, we introduce breakthroughs of mammalian haploid cells involving in mechanisms of self-diploidization, forward genetics for various targeting genes and imprinted genes related development.

Haploid pluripotent stem cells: twofold benefits with half the effort in genetic screening and reproduction

Haploid pluripotent stem cells, which are capable of self-renewal and differentiation into other cell types with only one set of chromosomes, have been established in several species from haploid embryos. Compared with diploid embryonic stem cells (ESCs), haploid embryonic stem cells (haESCs) are smaller in size, have a prolonged metaphase, and undergo self-doubling during culture. The monoallelic expression of haESCs provides great convenience for recessive inheritance research. Genetically modified haESCs also provide benefits in replacement of the gamete genomes, which not only facilitates the study of the function of imprinted genes but also potentially removes barriers to same-sex reproduction. In this review, we focus on strategies for obtaining haESCs and their potential applications in genetic screening, genomic imprinting, and unisexual reproduction.

Bioengineered microenvironment to culture early embryos

The abnormalities of early post-implantation embryos can lead to early pregnancy loss and many other syndromes. However, it is hard to study embryos after implantation due to the limited accessibility. The success of embryo culture in vitro can avoid the challenges of embryonic development in vivo and provide a powerful research platform for research in developmental biology. The biophysical and chemical cues of the microenvironments impart significant spatiotemporal effects on embryonic development. Here, we summarize the main strategies which enable researchers to grow embryos outside of the body while overcoming the implantation barrier, highlight the roles of engineered microenvironments in regulating early embryonic development, and finally discuss the future challenges and new insights of early embryo culture.

Current advances in haploid stem cells

Diploidy is the typical genomic mode in all mammals. Haploid stem cells are artificial cell lines experimentally derived in vitro in the form of different types of stem cells, which combine the characteristics of haploidy with a broad developmental potential and open the possibility to uncover biological mysteries at a genomic scale. To date, a multitude of haploid stem cell types from mouse, rat, monkey and humans have been derived, as more are in development. They have been applied in high-throughput genetic screens and mammalian assisted reproduction. Here, we review the generation, unique properties and broad applications of these remarkable cells.