What are Embryonic Stem Cells? [2023]

Interested in unlocking the complexities of embryonic stem cells?

Our article provides an exhaustive look into everything you need to know. From the basic principles of pluripotency and totipotency to advanced topics like cell culture and gene expression, we cover it all.

We also explore the promising applications of these cells in fields such as regenerative medicine and disease modeling while addressing the ethical and policy challenges that come with it. For a holistic understanding of this ever-evolving field, this is your go-to resource.

‍

What are Embryonic Stem Cells?

Embryonic stem cells (ESCs) are pluripotent stem cells harvested from the inner cell mass of a blastocyst, a preliminary stage in embryonic development around 4-5 days post-fertilization as per this study​. These cells are characterized by two principal attributes:

1. Pluripotency: ESCs can differentiate into any of the three germ layers: ectoderm, mesoderm, or endoderm, hence they possess the potential to generate every cell type within the human body, a fact underscored in this research​​.
2. Self-renewal: They have the capability to perpetually replicate while retaining their pluripotent state as detailed in this article​.

Key features of ESCs include

• They express high levels of pluripotency markers such as OCT4, SOX2, and NANOG as revealed in this report​.
• Characteristic high nucleus to cytoplasm ratio and prominent nucleoli are observed in ESCs, as discussed in this paper​.
• High telomerase activity supporting their self-renewal is demonstrated in this study​.
• Their culture necessitates particular conditions like growth on feeder layers of fibroblasts and the presence of factors like bFGF to deter spontaneous differentiation, as outlined in this research​.

The inherent pluripotency and self-renewal capabilities of ESCs render them indispensable for scientific research and a potentially invaluable source of cells for regenerative medicine. Nonetheless, ethical apprehensions surrounding the destruction of human embryos for ESC derivation persist. This ethical quandary has propelled the development of induced pluripotent stem cells (iPSCs), which are adult cells reverted to a pluripotent state without employing embryos, as illustrated in this paper​​.

Embryonic stem cells, sourced from early-stage embryos, are prized for their pluripotency and indefinite self-renewal capabilities. While they hold substantial promise for scientific and medical advancements, the ethical implications regarding their extraction remain a contentious issue.

Characteristics of Embryonic Stem Cells

Cell differentiation

Embryonic stem cells can transform into every cell type in the fetal body, a process referred to as cell differentiation. This capability allows them to generate diverse types of cells and is fundamental for the development of complex multicellular organisms.

Cell proliferation

Another key feature of ESCs is their rapid and unlimited capacity to divide and replicate while maintaining their undifferentiated state, referred to as cell proliferation. This key characteristic allows for the generation of large quantities of cells, which is crucial for research and possible clinical applications.

Self-renewal

Another fundamental property of ESCs is their ability to self-renew, meaning they can produce copies of themselves while maintaining their pluripotency and without changing their growth behavior or their chromatin and genomic structures.

Cell morphology

Embryonic stem cells have a unique cell morphology, with large nucleoli, high nuclear to cytoplomatic ratio, and compact colony formations in culture. Importantly, maintaining the appropriate morphology is critical for preserving the cells' pluripotent potential.

Cell markers such as Alkaline phosphatase, SSEA4, Tra-1-60, Tra-1-81, Oct4, Nanog, Sox2, Klf4, c-Myc

Embryonic stem cells exhibit several specific cell markers that evidence their pluripotent nature. Some of these markers include Alkaline phosphatase, an enzyme involved in cell differentiation, and surface markers such as SSEA4, Tra-1-60, and Tra-1-81. Several important gene products are also observed, including Oct4, Nanog, Sox2, Klf4, and c-Myc, which are the fundamental transcription factors driving and maintaining pluripotency.

Manipulating Embryonic Stem Cells in Lab

Cell culture techniques

Studying embryonic stem cells necessitates the development of effective cell culture techniques to ensure their growth and proliferation under controlled conditions. Critical aspects include appropriate culture media, substrate for the cells to grow on, and careful control of factors such as temperature and gas concentrations.

Usage of feeder cells

Feeder cells are often used in ESC culture to provide the essential growth factors necessary for their proliferation and maintenance of pluripotency. These feeder layers are usually mitotically inactivated fibroblast cells, which serve to enhance cell attachment and deliver necessary growth factors.

Growth factors

Various growth factors such as Leukemia Inhibitory Factor (LIF) and Fibroblast Growth Factor (FGF) are vital to maintain pluripotency and cell proliferation in embryonic stem cell cultures. These factors stimulate cell division and prevent differentiation, thereby assisting in the preservation of the undifferentiated state.

Transcription factors and gene expression

Maintaining the pluripotent state of ESCs relies heavily on the regulation of transcription factors and gene expression. Essential transcription factors like Oct4, Sox2, and Nanog are highly expressed in embryonic stem cells, helping preserve the cells’ undifferentiated state, while the repression of genes associated with differentiation promotes the maintenance of pluripotency.

Role of epigenetics

Epigenetic modifications, including DNA methylation and histone modification, play a crucial role in governing self-renewal and pluripotency of ESCs. They control the expression of key pluripotency and differentiation genes, thus deciding the cell fate.

Cell signaling importance

Signal transduction pathways are essential in directing the fate of embryonic stem cells. Specific signaling pathways like the Wnt, Notch, and Hedgehog pathways, regulate self-renewal, differentiation, and pluripotency.

Managing cell cycle

The manipulation of the cell cycle is critical when working with embryonic stem cells, as alterations can lead to unscheduled differentiation or loss of pluripotency. Hence, understanding the cell cycle regulators and their roles is important for maintaining the pluripotent state.

Interactions and Migrations of Embryonic Stem Cells

Understanding apoptosis

Apoptosis, or programmed cell death, has a significant role in embryogenesis, eliminating unrequired or atypical cells and shaping the embryonic structure. Therefore, a deep understanding of apoptosis mechanisms is crucial when studying or manipulating ESCs.

Cell adhesion

ESC adhesion, which is regulated by several cell adhesion molecules, is critical in managing their pluripotency, differentiation, and migration. It facilitates cell-cell interactions and communication with the extracellular matrix, which eventually shape cell behavior and fate.

Cell migration

Cell migration is significant during embryogenesis, with ESC migration influencing organogenesis and morphogenesis. Coordinating cell migration is crucial in embryogenesis, assisting cells in attaining their proper positions within the developing organism.

Cell metabolism

Studying the unique metabolic characteristics of ESCs is vital, given the critical link between cellular metabolism and stem cell fate decisions. ESCs have a distinct metabolic profile, utilizing glucose in an anaerobic manner despite the presence of oxygen, similar to cancer cells.

Cell Reprogramming and Inducing Pluripotent Stem Cells

Process of cell reprogramming

Cell reprogramming involves the conversion of a differentiated cell back into a pluripotent stem cell-like state—known as induced pluripotent stem cells (iPSCs)—through overexpression of specific transcription factors such as Oct4, Sox2, Klf4, and c-Myc. This technique provides a pathway for generating patient-specific pluripotent cells without using embryos.

Creating induced pluripotent stem cells

Induced pluripotent stem cells are bioengineered from adult somatic cells (skin or blood cells). The process involves reprogramming these mature cells back into pluripotent cells, which can then give rise to any cell type in the body similar to ESCs.

Comparison between embryonic stem cells and induced pluripotent stem cells

While ESCs and iPSCs are similar in their pluripotent nature, critical differences exist. ESCs are derived from embryos and are considered naturally pluripotent; in contrast, iPSCs are artificially reprogrammed from adult somatic cells. Moreover, iPSCs prove more valuable in patient-specific therapy due to the potential to match a patient's own genetic background, reducing the risk of immunological rejection.

Practical Applications of Embryonic Stem Cells

Cell transplantation

Embryonic stem cells, due to their pluripotency and ability to proliferate indefinitely, hold immense potential for regenerative medicine and cell therapies. They offer the possibility to generate specific cell types for transplantation into patients suffering from various degenerative diseases.

Tissue engineering and organoids

By directing the differentiation of ESCs, researchers can fabricate tissue-like 3D structures known as organoids. Such structures can mimic the organ's architecture and functionality, hence presenting opportunities for studying organ development, disease modeling, and potential organ replacement therapies.

Disease modeling

ESC-derived cells provide a valuable platform for modeling human diseases in vitro. Introduction of patient-specific genetic alterations into ESCs to create disease-specific lines allows for the study of pathogenesis, screening potential drug therapies, and understanding disease progression.

Drug screening

Embryonic stem cells may be used in drug discovery and testing. Given their ability to differentiate into various cell types, ESCs serve as a unlimited source of specific tissues required for drug testing, significantly improving the drug development process.

Regenerative medicine

ESCs offer a ray of hope for regenerative medicine, paving the way for therapies to regenerate damaged or lost tissues in diseases where currently no effective treatment is available. Potential applications include Parkinson's disease, heart disease, spinal cord injuries, and diabetes, to name a few.

Ethical and Regulatory Aspects Surrounding Embryonic Stem Cells

Debate over ethical issues

Embryonic stem cell research has sparked numerous ethical debates. The extraction of ESCs from the blastocyst typically results in its destruction, raising concerns around the status and rights of the early-stage embryo. Different societies hold varying views on when an embryo acquires the moral status of a person, leading to debates about the acceptability of ESC research.

Variety in stem cell policy worldwide

Stem cell policies vary globally, reflecting cultural, societal, and historic differences among countries. While some countries have restrictive legislation prohibiting embryonic stem cell research, others encourage the same, given the potential applications in understanding human development and treating diseases.

Role of ethics committees and legal regulations

Ethics committees and legal regulatory bodies play a crucial role in the oversight of ESC research, ensuring that studies conform to accepted ethical guidelines and legal rules. Their responsibility lies in sustaining the balance between promoting scientific advancement and ensuring respect for human life and dignity.

Clinical Trials and Therapies Using Embryonic Stem Cells

Current and completed clinical trials

Novel embryonic stem cell-based therapies are currently being studied in several clinical trials worldwide. Such studies target a diverse range of conditions, from eye disorders, such as age-related macular degeneration, to neurodegenerative diseases like Parkinson's disease.

Emerging cell therapies

Cell therapies using embryonic stem cells are emerging as potential treatments for numerous incurable diseases. Trials are ongoing for therapies aiming to replace lost or damaged cells in diseases like diabetes, heart disease, and spinal cord injuries, among several others.

Exploring Other Types of Stem Cells

Multipotent stem cells

Besides pluripotent ESCs and iPSCs, various multipotent stem cells exist, with the potential to differentiate into a limited number of cell types, usually within a particular lineage. The most notable examples are hematopoietic stem cells and mesenchymal stem cells.

Hematopoietic stem cells

Hematopoietic stem cells, found in bone marrow and umbilical cord blood, can generate all types of blood cells and are used in therapies to treat blood disorders such as leukemia and lymphoma.

Mesenchymal stem cells

Mesenchymal stem cells, typically found in bone marrow, adipose tissue, and umbilical cord blood, can differentiate into a variety of cell types, including osteocytes, chondrocytes, and adipocytes. They are explored extensively for their potential in tissue engineering and regenerative medicine.

Neural stem cells

Found in the brain, neural stem cells can differentiate into neurons and glial cells. Their manipulation presents promising routes for treating neurodegenerative diseases and injuries to the brain or spinal cord.

Cancer stem cells

Cancer stem cells are a small population of cells within tumors that have abilities similar to stem cells to self-renew and give rise to all cell types found in a particular cancer sample. Understanding these cells is crucial for developing novel cancer treatments.

Epiblast stem cells

Epiblast stem cells originate from the early mammalian embryo and share many similarities with ESCs in terms of pluripotency. However, they are isolated at a later developmental stage and hence, provide novel insights into developmental biology and pluripotency.

Trophoblast stem cells

Derived from the trophoblast, an outer layer of the blastocyst, trophoblast stem cells contribute to the formation of the placenta during development. They hold potential for studying placental biology and resolving pregnancy disorders linked to placental dysfunction.

Advanced Techniques and Challenges in Studying Embryonic Stem Cells

Role of genomics and genomic instability

Understanding ESC genomics is essential as ESCs often point to genomic instability, with chromosomal aberrations due to cultivation. Such instability can impact their differentiation capacity, tumorigenicity, and suitability for therapeutic applications.

Understanding cell senescence

Cell senescence, a state of irreversible cell cycle arrest, presents a significant challenge in the cultivation and utility of ESCs. Understanding the mechanisms driving senescence in ESCs is crucial to improve their maintenance and expand their potential applications.

Techniques like CRISPR genome editing and its limitations

Techniques like CRISPR/Cas9 have transformed the field of genetics, providing the tools to modify genes within ESCs precisely. Despite its power, challenges such as off-target effects and mosaicism persist, which could potentially lead to unexpected mutational consequences.

Challenges of mosaicism, off-target effects

While techniques like CRISPR/Cas9 have revolutionized gene editing, they also present challenges. Off-target effects, where modifications occur in non-targeted genes, present potential safety concerns. Likewise, mosaicism, where not all cells in a modified embryo carry the desired change, can complicate the interpretation of experimental results and potential clinical outcomes. Efforts to minimize such effects are crucial in improving the precision and safety of gene editing in ESCs.