Three papers published in Science detail the fate of every single cell produced to form an embryo in zebrafish and Xenopus (the western claw-toed frog).
'Understanding how an organism is made requires knowing which genes are turned on or off as cells make fate decisions, not just the static sequence of a genome,' said study co-author Dr Sean Megason at Harvard Medical School in Boston, Massachusetts. 'This is the first technological approach that has allowed us to systematically and quantitatively address this question.'
The scientists used a technique called single-cell RNA sequencing to reveal which genes were being expressed, in which cells, at different times. The researchers profiled more than 200,000 cells at multiple time points for both species over the course of the embryo's first day.
They also developed artificial DNA barcodes to tag each cell and so they could track the material of each cell individually.
As an embryo forms, individual cells will commit to becoming different cell types. 'In one snapshot, we can see the entire story of development unfolding,' Dr Allon Klein, also at Harvard Medical School, told STAT News. 'By capturing cells over the first 24 hours of life, we could look at the entire process by which cells were making decisions about the cell types they were going to become.'
A surprise finding was that some cell types emerged much earlier than previously thought.
The hope is that better understanding the process of cells differentiating may help in regenerative medicine, with the coaxing of stem cells into different tissue types. 'With these datasets, if someone wants to make a specific cell type, they now have the recipe for the steps that those cells took as they formed in the embryo,' said Klein.
Klein also told STAT: 'We could also use it to look at the dynamic of diseases such as developmental disorders or tumour development.'