Showing papers on "Totipotent published in 2020"

The molecular and cellular features of 2-cell-like cells: a reference guide.

Abstract: Currently, two main cell culture models predominate pluripotent stem cell research: embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). Thanks to their ability to contribute to and form all tissues within the body, ESCs and iPSCs have proven invaluable in understanding pluripotent states, early embryonic development and cell differentiation, as well as in devising strategies for regenerative medicine. Comparatively little is known about totipotency - a cellular state with greater developmental potential. In mice, only the zygote and the blastomeres of the 2-cell-stage embryo are truly totipotent, as they alone can develop to form the embryo and all of its supportive extra-embryonic tissues. However, the discovery of a rare subpopulation of cells in murine ESC cultures, possessing features of 2-cell embryo blastomeres and expanded cell fate potential, has provided a biochemically tractable model to enable the in vitro study of totipotency. Here, we summarize current known features of these 2-cell-like cells (2CLCs) in an effort to provide a reference for the community, and to clarify what we know about their identity so far.

From pluripotency to totipotency: an experimentalist's guide to cellular potency

Abstract: Embryonic stem cells (ESCs) are derived from the pre-implantation mammalian blastocyst. At this point in time, the newly formed embryo is concerned with the generation and expansion of both the embryonic lineages required to build the embryo and the extra-embryonic lineages that support development. When used in grafting experiments, embryonic cells from early developmental stages can contribute to both embryonic and extra-embryonic lineages, but it is generally accepted that ESCs can give rise to only embryonic lineages. As a result, they are referred to as pluripotent, rather than totipotent. Here, we consider the experimental potential of various ESC populations and a number of recently identified in vitro culture systems producing states beyond pluripotency and reminiscent of those observed during pre-implantation development. We also consider the nature of totipotency and the extent to which cell populations in these culture systems exhibit this property.

A transcriptional roadmap for 2C-like-to-pluripotent state transition.

Abstract: In mouse embryonic stem cell (ESC), a small cell population displays totipotent features by expressing a set of genes that are transiently active in 2-cell–stage embryos. These 2-cell–like (2C-like) cells spontaneously transit back into the pluripotent state. We previously dissected the transcriptional dynamics of the transition from pluripotency to the totipotent 2C-like state and identified factors that modulate the process. However, how 2C-like cells transit back into the pluripotent state remains largely unknown. In this study, we analyzed the transcriptional dynamics from the 2C-like state to pluripotent ESCs and identified an intermediate state. The intermediate state characterized by two-wave step up-regulation of pluripotent genes is different from the one observed during the 2C-like entry transition. Nonsense-mediated Dux mRNA decay plays an important role in the 2C-like state exit. Thus, our study not only provides a transcriptional roadmap for 2C-like–to–pluripotent state transition but also reveals a key molecular event driving the transition.

A distinct metabolic state arises during the emergence of 2-cell-like cells

Abstract: Pluripotent stem cells are thought of as a surrogate of early developmental stages that sustain the capacity to generate all cell types in the body, thereby constituting an invaluable tool to address the mechanisms underlying cellular plasticity. In the mouse, cells resembling totipotent 2-cell-stage embryos (2-cell-like cells) arise at a very low frequency in embryonic stem cell (ESC) cultures. However, the extent to which these early-embryonic-like cells recapitulate the molecular features of the early embryo is unclear. Here, we have undertaken a characterization of some of the metabolic features of early-embryonic-like cells in culture. Our data indicate that early-embryonic-like cells exhibit decreased glycolytic and respiratory activity, lower levels of reactive oxygen species and increased glucose uptake, suggesting a shift of the metabolic programme during 2-cell-like cell reprogramming. Accordingly, we find that 2-cell-like cells can be induced by defined metabolites. Thus, in addition to their transcriptional and chromatin features, 2-cell-like cells recapitulate some of the metabolic features of their in vivo counterpart. Altogether, our work underscores a distinct metabolic state of early-embryonic-like cells and identifies compounds that can induce their emergence in vitro.

Defining totipotency using criteria of increasing stringency

Abstract: Totipotency is the ability of a single cell to give rise to all the differentiated cells that build the conceptus, yet how to capture this property in vitro remains incompletely understood. Defining totipotency relies upon a variety of assays of variable stringency. Here we describe criteria to define totipotency. We illustrate how distinct criteria of increasing stringency can be used to judge totipotency by evaluating candidate totipotent cell types in the mouse, including early blastomeres and expanded or extended pluripotent stem cells. Our data challenge the notion that expanded or extended pluripotent states harbor increased totipotent potential relative to conventional embryonic stem cells under in vivo conditions.

Specification of the First Mammalian Cell Lineages In Vivo and In Vitro

Abstract: Our understanding of how the first mammalian cell lineages arise has been shaped largely by studies of the preimplantation mouse embryo. Painstaking work over many decades has begun to reveal how a single totipotent cell is transformed into a multilayered structure representing the foundations of the body plan. Here, we review how the first lineage decision is initiated by epigenetic regulation but consolidated by the integration of morphological features and transcription factor activity. The establishment of pluripotent and multipotent stem cell lines has enabled deeper analysis of molecular and epigenetic regulation of cell fate decisions. The capability to assemble these stem cells into artificial embryos is an exciting new avenue of research that offers a long-awaited window into cell fate specification in the human embryo. Together, these approaches are poised to profoundly increase our understanding of how the first lineage decisions are made during mammalian embryonic development.

Polyploidy of semi-cloned embryos generated from parthenogenetic haploid embryonic stem cells

Abstract: In mammals, the fusion of two gametes, an oocyte and a spermatozoon, during fertilization forms a totipotent zygote. There has been no reported case of adult mammal development by natural parthenogenesis, in which embryos develop from unfertilized oocytes. The genome and epigenetic information of haploid gametes are crucial for mammalian development. Haploid embryonic stem cells (haESCs) can be established from uniparental blastocysts and possess only one set of chromosomes. Previous studies have shown that sperm or oocyte genome can be replaced by haESCs with or without manipulation of genomic imprinting for generation of mice. Recently, these remarkable semi-cloning methods have been applied for screening of key factors of mouse embryonic development. While haESCs have been applied as substitutes of gametic genomes, the fundamental mechanism how haESCs contribute to the genome of totipotent embryos is unclear. Here, we show the generation of fertile semi-cloned mice by injection of parthenogenetic haESCs (phaESCs) into oocytes after deletion of two differentially methylated regions (DMRs), the IG-DMR and H19-DMR. For characterizing the genome of semi-cloned embryos further, we establish ESC lines from semi-cloned blastocysts. We report that polyploid karyotypes are observed in semi-cloned ESCs (scESCs). Our results confirm that mitotically arrested phaESCs yield semi-cloned embryos and mice when the IG-DMR and H19-DMR are deleted. In addition, we highlight the occurrence of polyploidy that needs to be considered for further improving the development of semi-cloned embryos derived by haESC injection.

Relaxed 3D genome conformation facilitates the pluripotent to totipotent state transition in embryonic stem cells

Abstract: The 3D genome organization is crucial for gene regulation. Although recent studies have revealed a uniquely relaxed genome conformation in totipotent early blastmeres of both fertilized and cloned embryos, how weakened higher-order chromatin structure is functionally linked to totipotency acquisition remains elusive. Using low-input Hi-C, ATAC-seq, and ChIP-seq, we systematically examined the dynamics of 3D genome and epigenome during pluripotency-to-totipotency transition in mouse embryonic stem cells (ESCs). The totipotent 2-cell-embro-like cells (2CLCs) exhibit more relaxed chromatin architecture compared to ESCs, including global weakening of both enhancer-promoter interactions and TAD insulation. While the former leads to inactivation of ESC enhancers and down-regulation of pluripotent genes, the latter may facilitate contacts between the new enhancers arising in 2CLCs and neighboring 2C genes. Importantly, disruption of chromatin loops by depleting CTCF or cohesin promotes ESC to 2CLC transition. Our results thus establish a critical role of 3D genome organization in totipotency acquisition. HIGHLIGHTSO_LIGlobal weakening of the 3D genome conformation during ESC to 2CLC transition C_LIO_LILoss of enhancer-promoter loops and down-regulation of pluripotent genes in 2CLCs C_LIO_LIInactivation of ESC enhancers and formation of new enhancers in 2CLCs C_LIO_LIDisruption of chromatin loops by depleting CTCF or cohesin promotes 2CLC emergence C_LI

Chromatin Accessibility Dynamics and a Hierarchical Transcriptional Regulatory Network Structure for Plant Somatic Embryogenesis

Abstract: Plant somatic embryogenesis refers to a phenomenon where embryos develop from somatic cells in the absence of fertilization. It provides a powerful system to produce genetically modified crops as well as to obtain artificial seeds. Previous studies have revealed that somatic embryo formation can be achieved by the treatment of somatic tissues with auxin, ectopic overexpression of a specific transcription factor, or the disruption of certain chromatin-modifying proteins. However, how auxin induces the cell totipotent state and how transcription factors trigger somatic embryogenesis are poorly understood. Here, we show that auxin rapidly rewires the cell totipotency network by altering chromatin accessibility. The analysis of chromatin accessibility dynamics further reveals a hierarchical gene regulatory network underlying somatic embryogenesis. Particularly, we find that the embryonic nature of explants is a prerequisite for somatic cell reprogramming. Upon cell reprogramming, the B3-type totipotent transcription factor LEC2 promotes somatic embryo formation by direct activation of the early embryonic patterning genes WOX2 and WOX3. Our results thus shed light on the molecular mechanism by which auxin promotes the acquisition of plant cell totipotency, and establish a direct link between cell totipotent genes and the embryonic development pathway.

Compositions and methods for reprogramming cells and for somatic cell nuclear transfer using duxc expression

Abstract: It was found that DUXC family proteins were efficient activators of EGA and that DUXC proteins could be used in methods in the reprogramming of cells to a totipotent state and to increase the efficiency of somatic cell nuclear transfer (SCNT). Accordingly, aspects of the disclosure relate to a method for reprogramming a cell into a totipotent state, the method comprising expressing a DUXC family protein in the cell. Further aspects of the disclosure relate to a method for making a host cell nuclear transfer (SCNT) embryo comprising expressing a DUXC protein in a somatic cell and transferring the nucleus of the somatic cell to an enucleated oocyte, thereby making a SCNT embryo.

Stem Cells and the Basics of Immunology

Abstract: In this chapter, we expand on the concept of stem cell potency. We cover different degrees of cell stemness, including cell ability to differentiate into specialized cells, i.e., being totipotent, pluripotent, multipotent, or oligopotent. We discuss the promise, the advantages, and the possible shortcomings of using stem cells in tissue engineering and give three examples of detailed differentiation protocols. The second part of the chapter deals with the possibility of tissue-engineered organs being rejected by the recipient’s immune system. Here we briefly overview the main principles of immune rejection and discuss how one can bypass it by using induced pluripotent stem cells.

Polyploidy of semi-cloned embryos generated from parthenogenetic haploid embryonic stem cells

Abstract: In mammals, the fusion of two gametes, an oocyte and a spermatozoon, during fertilization forms a totipotent zygote. There has been no reported case of natural parthenogenesis, in which embryos develop from unfertilized oocytes. The genome and epigenetic information of haploid gametes are crucial for the proper development of embryos. Haploid embryonic stem cells (haESCs) are unique stem cells established from uniparental blastocysts and possess only one set of chromosomes. Previous studies have shown that sperm or oocyte genome can be replaced by haESCs with or without manipulation of genomic imprinting for generation of mice. Recently, these remarkable semi-cloning methods have been applied for screening of key factors of mouse embryonic development. While haESCs have been applied as substitute of gametic genome, the fundamental mechanism how haESCs contribute to the genome of totipotent embryos is unclear. Here, we show the generation of fertile semi-cloned mice by injection of parthenogenetic haESCs (phaESCs) into oocytes after deletions of two differentially methylated regions (DMRs), the IG-DMR and H19-DMR. For characterizing the genome of semi-cloned embryos further we establish ESC lines from semi-cloned blastocysts. We report that polyploid karyotypes are observed frequently in semi-cloned ESCs (scESCs). Our results confirm that mitotically arrested phaESCs provide high efficiency for semi-cloning when the IG-DMR and H19-DMR are deleted. In addition, we highlight the occurrence of polyploidy that needs to be considered for further improvement for development of semi-cloned embryos derived by haESC injection.

Preimplantation Development: From Germ Cells to Blastocyst

Abstract: In mammals, after germ cells have arrived in the gonads, they have to undergo several steps to become cells that are competent of forming a totipotent zygote after fusion. The zygote undergoes a series of cleavage divisions which will give rise to a morula stage embryo. At around this stage, the first lineage segregation event takes place leading to the formation of an outer trophectoderm layer and a pluripotent inner cell mass that will give rise to the fetus. In a second lineage segregation event, NANOG-expressing cells form the pluripotent epiblast while GATA4/6-expressing cells will give rise to the yolk sac. Around this time, the blastocyst stage embryo arrives at the uterus for implantation. Blastocyst stage embryos of mouse and human have an invasive type of implantation, while embryos of other mammalian species can have a more superficial type of implantation.

Nanoscience Research in Regenerative Medicine

Abstract: Stem cells are undifferentiated cells which can either proliferate in their undifferentiated states, or differentiate into cells of other lineages. They can be classified according to their potency, or differentiation potential, or according to their origin. Stem cells can be totipotent, pluripotent, multipotent, oligopotent or unipotent, depending on types of cells they can differentiate into. On the other hand, stem cells can be of embryonic origin or adult tissue origin. Embryonic stem cells are pluripotent in nature and are obtained from the blastocyst of the embryo. On the other hand, adult stem cells, like mesenchymal stem cells of various tissues such as bone marrow, adipose tissue, umbilical cord and amniotic fluid, are generally multipotent. Stem cells, mainly mesenchymal stem cells, have been used as therapy in several diseases. In this chapter, we have highlighted some of the therapeutic strategies using stem cells for degenerative diseases of the lungs and kidneys.

Embryology of the Vertebral Column

Abstract: The fertilized egg (or first embryonic cell) is described as totipotent because it is capable of giving birth to an entire embryo. Embryonic development is the consequence of the gene activity within the cells and the interactions received by this cell from its environment. The result is changes in shape, movement, proliferation and death, differentiation, and specialization of cells.

CTCF is a Barrier for Totipotent-like Reprogramming

Abstract: SUMMARY Totipotent cells have the ability of generating embryonic and extra-embryonic tissues1,2. Interestingly, a rare population of cells with totipotent-like potential was identified within ESC cultures3. These cells, known as 2 cell (2C)-like cells, arise from ESC and display similar features to those found in the totipotent 2 cell embryo2-4. However, the molecular determinants of 2C-like conversion have not been completely elucidated. Here, we show that CTCF is a barrier for 2C-like reprogramming. Indeed, forced conversion to a 2C-like state by DUX expression was associated with DNA damage at a subset of CTCF binding sites. Endogenous or DUX-induced 2C-like ESC showed decreased CTCF enrichment at known binding sites, suggesting that acquisition of a totipotent-like state is associated with a highly dynamic chromatin architecture. Accordingly, depletion of CTCF in ESC efficiently promoted spontaneous and asynchronous conversion to a totipotent-like state. This phenotypic reprogramming was reversible upon restoration of CTCF levels. Furthermore, we showed that transcriptional activation of the ZSCAN4 cluster was necessary for successful 2C-like reprogramming. In summary, we revealed the intimate relation between CTCF and totipotent-like reprogramming.