Cell by Cell, Scientists Map the Genetic Steps as Eggs Become Animals

Jordana Cepelewicz in Quanta:

ScreenHunter_3070 Apr. 28 19.23

A fertilized egg divides first into two cells, then four, then eight and so on. Meanwhile, those cells progress from undifferentiated blobs in a cluster to more diverse identities associated with heart, brain, muscle, blood, bone and other tissues. Though the overall process is familiar, scientists have not understood it in much detail.

But three papers appearing today in Science are changing that, as they unveil work with major significance for the field of developmental biology. Using a combination of gene sequencing and mathematical methods, the researchers traced the patterns of gene expression in every cell in embryos of zebra fish and of Western clawed frogsthrough many stages of development during their first 24 hours.

The results revealed, at a previously impossible resolution and scale, the genetic and developmental trajectories that embryonic cells follow to their eventual fates in fully differentiated tissues. Surprising new insights emerged as well: Many biologists, for example, believed that embryonic cells always followed branching paths toward maturity that committed them irrevocably to certain fates. But the new data indicates that cells can, in effect, sometimes “loop back” to follow a different path, and that cells with different developmental histories can sometimes end up as the same type of cell.

More here. [Thanks to Stefan Saal.]