NANOG Gene: Cambridge Base Editing Study Reveals Why Humans Are Not Mice

In June 2026, a team led by developmental biologist Kathy Niakan at the University of Cambridge's Loke Centre for Trophoblast Research published the first study to use base editing in human embryos to investigate gene function . By deactivating the NANOG gene with a technique called adenine base editing (ABE), the researchers uncovered a startling finding about early human development — and a dramatic difference between human and mouse biology that has significant implications for both basic science and the ethics of heritable genome editing .

The findings, published in Nature, prompted coverage with headlines such as "Precise genome editing of human embryos triggers praise and alarm" and "'Edited' human embryos reveal secrets of our development — and fuel ethical debate" .

What the Cambridge Team Discovered About NANOG

The team used adenine base editing (ABE) to disrupt the NANOG gene in donated early human embryos. They found that NANOG is essential for forming the future body — without it, embryonic cells lose the ability to differentiate into the epiblast, the cell lineage that gives rise to the fetus. Instead, the cells default toward placental (trophectoderm) lineages, meaning the embryo cannot proceed to form the body .

A related bioRxiv preprint from Columbia University researchers had shown earlier in June 2026 that base editing in human embryos was efficient and, unlike Cas9-induced double-strand breaks, did not result in chromosomal abnormalities or large deletions .

How Base Editing Compares to Conventional CRISPR/Cas9

Base editing is a modified version of CRISPR that does not create double-strand DNA breaks (DSBs). Instead, it uses a catalytically impaired Cas9 fused to a deaminase enzyme to directly convert one DNA base into another (e.g., C→T or A→G) .

Feature	Conventional CRISPR/Cas9	Base editing
Mechanism	Creates double-strand breaks (DSBs)	No DSB; direct chemical conversion of a single base
Repair pathway	Relies on NHEJ or HDR	No reliance on DSB repair
Unintended indels	Common (byproduct of NHEJ)	Rare or absent
Chromosomal abnormalities	Can cause large deletions, rearrangements	Not observed in human embryo study
Off-target edits	Well-documented	Also documented; some studies show high-fidelity ABEs can still induce off-target sites comparable to or exceeding Cas9

The key trade-off is clear: base editing avoids the structural havoc that Cas9-induced DSBs often cause, making it much cleaner at the target site . However, base editors have their own off-target editing and "bystander" edits (editing nearby bases within the activity window). A 2026 study found that certain high-activity base editors (e.g., ABE8e) can produce more off-target sites than Cas9 nuclease under controlled conditions .

Species-Specific Differences: Human vs. Mouse Embryos

One of the most significant discoveries of the study was a striking difference in how human and mouse embryos respond to NANOG loss :

• In mouse embryos (from prior studies): Loss of Nanog causes early embryonic lethality, but the embryo can still initiate some differentiation. Nanog is known to maintain pluripotency in the inner cell mass .
• In human embryos (this study): When NANOG was disrupted, the cells of the inner cell mass failed to form the epiblast (future body) and instead almost entirely redirected toward the trophectoderm (placental) lineage. The loss was more profound and the cell-fate decision was more rigid than in mice .

Independent experts commenting on the study said the findings were "striking" — that the human embryo appears to have a more stringent requirement for NANOG to establish the epiblast lineage compared to the mouse, underscoring the importance of studying human development directly rather than relying solely on animal models .

Ethical Implications and Regulatory Context

The study triggered both praise and alarm . Key ethical issues raised include:

• Heritable germline editing: Although this study was basic research (not aimed at pregnancy), it used a technique that could theoretically be applied in a clinical, heritable context. Any edits introduced in an embryo could be passed to future generations .
• Off-target and unintended effects: Despite base editing's improved precision, off-target edits and bystander mutations remain a significant concern for any future clinical use .
• Slippery slope concerns: Some bioethicists worry that demonstration of feasibility in research embryos brings the world closer to "designer babies" or non-medical enhancement .
• Consent and welfare: The Nuffield Council on Bioethics has concluded that heritable genome editing could be ethically acceptable only if it is intended to secure the welfare of the future person and does not increase disadvantage or discrimination. Most bodies agree the technology is not yet safe enough for clinical use .

The research was conducted under a license from the UK Human Fertilisation and Embryology Authority (HFEA) , which permits gene-editing research on embryos for basic science — but not for implantation . The HFEA's statutory framework (HFE Act 1990) requires that any licensed embryo research have a clear scientific justification, meet ethical standards, and have no viable alternative to using embryos .

Heritable genome editing for reproduction remains illegal in the UK. The HFEA has stated that genome editing is not yet sufficiently precise or controllable to permit safe clinical use . The WHO has also published a governance framework calling for a cautious, stepwise approach with broad public debate before any heritable genome editing is considered . Other countries (e.g., China, USA) have varying regulatory frameworks, but there is broad international consensus against clinical heritable editing at this stage .