For the first time, scientists zoom in on one of the earliest phases of the human embryo

Amazing stuff! Unfortunately, no pictures! Research article is behind paywall!

"... Gastrulation occurs around 14 days or so after the egg is fertilized but everything we know about this essential phase of embryonic development comes from studies on animals. Scientists in the UK are not allowed to culture embryos in the lab for more than 14 days for ethical reasons as gastrulation also marks the development of the nervous system. But the researchers were able to study a human embryo sample that was around 16 to 19 days of age, sourced from a woman who decided to abort her pregnancy and donate the embryo to science. Most people don’t even know they’re pregnant in the first three weeks following fertilization, which is why such embryos are so rare and challenging to study. ...
Perhaps rather surprisingly, this investigation showed that gastrulation is very similar to what mouse embryos go through. One of the notable differences is that, in human embryos, early forms of blood cells appear earlier than in mice.

But, by far, the most important finding was that this particular embryo had no nervous system, unlike mice who go on to form their first neurons by week two of gestation.

This means that we now have evidence that puts into question the 14-day limit on culturing embryos, something that could have a profound impact on research and medicine in general. ..."

From the abstract:

"... Here we characterize in a spatially resolved manner the single-cell transcriptional profile of an entire gastrulating human embryo, staged to be between 16 and 19 days after fertilization. We use these data to analyse the cell types present and to make comparisons with other model systems. In addition to pluripotent epiblast, we identified primordial germ cells, red blood cells and various mesodermal and endodermal cell types. This dataset offers a unique glimpse into a central but inaccessible stage of our development. ..."

For the first time, scientists zoom in on one of the earliest phases of the human embryo Gastrulation used to be a black box. Now we know what exactly happens during this critical phase of embryonic development.

Single-cell transcriptomic characterization of a gastrulating human embryo (no public access)