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Embryonic stem cells (ES cells, ESCs) are cultured cells derived from the inner cell mass or epiblast of early embryos that can keep dividing in the lab and can contribute to all tissues of an embryo. This page explains them as a research reagent: how mouse ES cells (mESCs) are used and maintained, and which oversight documents lab staff check before working with human ES cells (hESCs). It is general information for researchers and lab staff, not medical advice.
Short answer: what are ES cells?
ES cells are karyotypically normal cells derived from the inner cell mass (ICM) or epiblast of peri-implantation embryos (Morgani et al. 2013, Cell Reports 3(6):1945-1957). They can be grown in culture and, when put back into an embryo, contribute to all embryonic tissues but not to extraembryonic tissues. That combination, indefinite culture plus a wide developmental potential, is why labs use them.
Definition and scope
“ES cells” is the lab shorthand for embryonic stem cells; “mESCs” means mouse ES cells and “hESCs” means human ES cells. In the Morgani et al. paper, ES cells are described as able to contribute to all tissues of the embryo but not extraembryonic tissues, which is why they are usually called pluripotent rather than totipotent. The same paper reports work on whether cells with broader potential arise under particular culture conditions, so the boundary is an active research question rather than a settled textbook line.
Induced pluripotent stem cells are a different cell type made by reprogramming; see the CASRAI guide to induced pluripotent stem cells. The ethical and legal debate around deriving hESCs is covered separately in ethics of embryonic stem cell research.
How labs use ES cells in practice
Culture conditions for mouse ES cells
Morgani et al. report that mouse ES cells can be maintained in the presence of LIF (leukaemia inhibitory factor) and either BMP4 or serum. Ying et al. (2008, Nature 453:519-523) described a “ground state” culture in which dual inhibition of MEK and GSK3 (known as 2i) supports mouse ES cell self-renewal in serum-free medium, with LIF further helping; Morgani et al. describe the 2i inhibitors as shielding ES cells from differentiation-inducing signals. Exact reagent concentrations belong in a validated protocol from the originating paper or the cell line’s supplier, not in a summary.
Gene targeting and reporter lines
Because ES cells divide in culture and can contribute to the embryo, a genetic change made in a dish can be studied in a whole animal. Morgani et al., for example, built a reporter line by homologous recombination. This gene-targeting route is the main reason mESCs are standard laboratory tools.
What “differentiation” means here
Cell differentiation is the process by which a cell becomes specialised for a particular tissue or function. The 2i conditions described above work by shielding ES cells from differentiation-inducing signals.
Related concepts and a sourced comparison
| Item | What the source states | Source |
|---|---|---|
| Where ES cells come from | Inner cell mass or epiblast of peri-implantation embryos | Morgani et al. 2013 |
| Mouse ES cell maintenance | LIF with BMP4 or serum | Morgani et al. 2013 |
| Ground-state culture | 2i (MEK and GSK3 inhibition), serum-free, with LIF helping | Ying et al. 2008 |
| Developmental potential | Contribute to all embryo tissues, not extraembryonic tissues | Morgani et al. 2013 |
| Genetic modification | Reporter line made by homologous recombination | Morgani et al. 2013 |
Where it matters for labs: an oversight checklist for hESC work
Before ordering or using hESC lines, lab staff typically look at three documents; this is a pointer list, not a legal conclusion.
- ISSCR Guidelines for Stem Cell Research and Clinical Translation. The International Society for Stem Cell Research published the guidelines in 2021; the current version is the August 2025 Update, Version 1.2, which is limited to stem cell-based embryo models, and all other sections remain as published in 2021. Section 2 is “Laboratory-based Human Embryonic Stem Cell Research, Embryo Research, and Related Research Activities” (isscr.org/resources/guidelines-for-stem-cell-research, read 2026-11-07).
- NIH rules for NIH-funded work. The 2009 NIH Guidelines limit NIH funding of hESC research to lines derived from surplus IVF embryos with informed consent. See the dictionary entry NIH Guidelines for Human Stem Cell Research and confirm the current registry status with NIH before relying on a specific line.
- Your institution’s stem cell oversight committee. The CASRAI ethics guide describes the ESCRO (embryonic stem cell research oversight) arrangement; check what your institution requires before starting.
- Outside the US. For the UK framework, see the dictionary entries on the UK Stem Cell Bank and the HFEA.
Common misunderstandings
- “ES cells are totipotent.” The usual description is pluripotent: contributing to all embryo tissues but not extraembryonic tissues.
- “ES cells and iPS cells are the same.” They are different cell types with different origins.
- “Mouse and human ES cell rules are the same.” Human ES cell work has its own oversight documents (above); the culture details quoted here are for mouse cells.
FAQ
What are embryonic stem cells, simply?
Cells taken from the inner part of an early embryo and grown in the lab, where they can multiply and later become many specialised cell types.
What are the functions of embryonic stem cells?
In an embryo, the cells of the inner cell mass give rise to the embryo’s tissues. In the lab, ES cells serve as a renewable source of cells and as a vehicle for gene targeting, for example in reporter lines and chimeras.
What is cell differentiation?
The process by which a cell becomes specialised for a particular tissue or function.
What is embryonic tissue?
Tissue of the embryo. In ES cell terms, the cells contribute to all embryonic tissues but not to extraembryonic tissues such as those that support the embryo.
Do embryonic stem cells come from aborted fetuses?
No. ES cells are derived from the inner cell mass or epiblast of early embryos. Under the 2009 NIH Guidelines, NIH-funded hESC research is limited to lines from surplus IVF embryos donated with informed consent.
Is human embryonic stem cell research illegal?
That depends on the country, funder and institution, and this page does not give legal conclusions. See the ethics and policy guide for the US and UK frameworks.
Which diseases can be cured by stem cell therapy?
This page does not make cure claims. Laboratory ES cell research and clinical cell therapy are separate matters; clinical translation is addressed in the ISSCR guidelines and regulated by bodies such as the FDA. Individuals should ask a clinician about treatment questions.
Sources
- Morgani SM et al. (2013). Totipotent embryonic stem cells arise in ground-state culture conditions. Cell Reports 3(6):1945-1957. pmc.ncbi.nlm.nih.gov/articles/PMC3701323 (read 2026-11-07).
- Ying QL et al. (2008). The ground state of embryonic stem cell self-renewal. Nature 453:519-523.
- ISSCR, Guidelines for Stem Cell Research and Clinical Translation, August 2025 Update, Version 1.2: isscr.org (read 2026-11-07).
- NIH Guidelines on Human Stem Cell Research (2009), as summarised in NIH archived pages.
