How does a single fertilised egg turn into a body with organs, skin and blood? Scientists have wanted to read that story cell by cell for over a century. A team led by the University of Washington School of Medicine has now used a tool called DNA Typewriter to record the family tree of cells in a developing mouse embryo, from its very first division to 13.5 days of development. The study appeared in Science on October 8, 2026.
What is DNA Typewriter?
DNA Typewriter was invented by Dr. Jay Shendure of UW Medicine and Dr. Junhong Choi of Sloan Kettering Cancer Center. It is a genome-editing-based recorder that writes into a stretch of DNA called a “tape”.
“Think of it like an actual typewriter, except it types onto a cell’s own DNA instead of paper,” said Haedong Kim, a co-first author. “Every time a cell divides, it strikes one new character onto the next blank line — always in order, never overwriting what’s already there.”
When scientists later read these codes, cells that share the same early markings must share a common ancestor. Put enough of them together and you get a family tree of the whole embryo.
How DNA Typewriter recorded a mouse embryo
The team put a redesigned tape into the genome of fertilised mouse eggs. The new design made it much easier to read the recording back out of single cells, which mattered because of the scale involved.
- They tried the recording in 100 fertilised eggs and ended up with 10 embryos to examine.
- One of them, Embryo No. 3, had the richest recording, so the team focused its full analysis on it.
- From that embryo they profiled about 1.3 million cells.
- Recording ran from the first cell division to day 13.5, when organs are taking shape. Mouse pregnancy lasts about 19 to 21 days.
The researchers say older methods often cut DNA, which is harsher on cells, can erase earlier records and runs out of space quickly. They also leave marks in no set order. DNA Typewriter writes without fully cutting the DNA and records in strict time order.
What the family tree revealed
The recording left a clear mark separating the two very first cells, so nearly every profiled cell could be traced back to one or the other. One of those two cells produced more descendants, yet both contributed diverse cell types in almost equal ratios.
The team could also see when each cell type split off onto its own path. Blood cells and the retina committed early, while the outer layer of skin committed noticeably later. In other words, cells don’t all pick their identity at once.
Limits and open questions
This is mouse research, and the detailed findings come from a single embryo out of 100 attempts, so it’s an early demonstration rather than a routine method. It records development up to day 13.5, not a full pregnancy. The University of Washington has filed a patent application related to DNA Typewriter, and the authors disclosed that AI-based tools supported data exploration, analysis, coding and manuscript writing. Some readers may also have ethical questions about recording technology placed in embryos, even animal ones, and those deserve open discussion as tools like this improve.
Why this matters
As a writer, I think the typewriter idea is one of the most elegant things I’ve read about this year: a body keeping its own diary, one letter per division. The researchers link this work to understanding birth defects, neurodevelopmental conditions, genetic disorders and cancer, and I can see why that’s exciting. At the same time, I’d keep expectations grounded. It’s one mouse embryo, the method is patented and still new, and the path from a mouse family tree to helping patients is long. I’d love to hear where you land on it.
For more on how DNA shapes life, read Cambridge scientists find a hidden layer of DNA information and India’s $691 billion bioeconomy roadmap.