Embryology: Insights into early human development

The first detailed cellular and molecular examination of a human embryo in the process of gastrulation, an important event in early development, is presented online in this week’s Nature. The findings offer a unique insight into a central, but sometimes inaccessible, stage of human development.

Gastrulation is a defining moment in early human development. This process starts approximately 14 days after fertilization and continues for slightly over a week. Currently, our understanding of human gastrulation is largely limited to experimental models, and is yet to be studied directly, as human embryos at this stage have been difficult to obtain, in part because the culture of human embryos has previously been limited to 14 days after fertilization by international guidelines.

Shankar Srinivas and colleagues analysed a single human embryo, donated to research after voluntary termination of pregnancy, at a stage corresponding to between 16 and 19 days after fertilization, and provide a detailed description of the cell types present and of the genes they express, making comparisons with experimental models. The authors detected primordial germ cells (precursor cells that give rise to egg or sperm cells) and red blood cells, among others. Additionally, they found that cell specification in the nervous system had not yet begun at this stage of development.

Although only a single embryo was studied, the findings provide new context for interpreting experiments in other model systems. These data also offer unique insights into human gastrulation, a previously unexplored and fundamental stage of human embryonic development, the authors conclude.