‘This cell will self-destruct in 5 days’ – Written by Charlotte Harrison, Science Writer.
A team of researchers have used single-cell transcriptome data from human embryos to identify a type of cell which self-destructs within days of forming. The cell acts as part of a quality control process to protect the developing foetus.
The study provides insights into the first stages of development after fertilisation and might improve IVF or regenerative medicine treatments in the future.
Mission impossible
After fertilisation, the zygote divides, and the mission of the resulting cells — should they choose to accept it — is to become specialist cells that form the placenta and embryo. By analysing the single-cell transcriptome data of marker genes in 5-day-old embryos, the researchers discovered around a quarter of the cells didn’t fit the profile of any known cell types.
Further study showed that these ‘unknown’ cells contained young transposable elements or jumping genes; rogue elements of DNA that can self-copy and re-insert into DNA, often causing damage in the process.
Moreover, the decedents of these cells had DNA damage and underwent apoptosis – or self-destruction.
Mission accomplished
The single-cell data also showed that the key cells that become the embryo (the inner cell mass) don’t contain jumping genes but express a virus-like gene instead. The presence of this gene helps suppress the young jumping genes in the inner cell mass, enabling the cells to survive.
The researchers suggest that the process of selective cell destruction is a form of quality control that selects good cells for further development.
“We are used to the idea of natural selection favouring one organism over another. What we are seeing within embryos also looks like survival of the fittest but this time between almost identical cells. It looks like we’ve uncovered a novel part of our arsenal against these harmful genetic components, ” said the authors in a press release.
The researchers speculate that if the quality control process is too sensitive, the embryo may not be viable. This notion might explain why some mutations that detect damage in early embryos are also associated with infertility.
