New Scientist, 22nd March 2021
THE human placenta is riddled with cancer-like patterns of mutations. But the discovery is better news than it might appear: it is helping scientists open a new window on the mysterious world of early human development.
In some ways, the placenta is a forgotten organ. It begins to form shortly after fertilisation from the embryo’s cells and then helps to support the future fetus as it develops before being discarded at birth.
But it is difficult to study how embryos “decide” which cells are destined for the placenta and which for the fetus.
“So far, we’ve been blind to the first split,” says Tim Coorens at the Wellcome Sanger Institute near Cambridge, UK.
Coorens and his colleagues, including his PhD supervisor Sam Behjati, decided to retrace the lineages of cells in full-term placentas to see where they came from.
Their approach relies on the fact that cells naturally accumulate mutations in their DNA and then pass these on when they divide. By comparing patterns of mutations between samples, it is possible to trace cells’ family trees back in time…