Embryonic development progresses through distinct stages before forming a fully developed human. While later in-utero phases are well-documented, gastrulation—occurring just days after fertilization—has remained elusive. A pioneering study from the University of Cambridge now sheds new light on this vital process.
Gastrulation marks the second phase of embryonic development, where blastomeres—cells from the fertilized egg's initial divisions—reorganize into two or three layers: an outer ectoderm, a middle mesoderm (in triploblastic organisms), and an inner endoderm. This transforms the embryo from a single-layered disc into a multi-layered structure.
Gastrulation typically begins between the fourteenth and fifteenth day of development. Ethical guidelines have historically limited lab cultivation of human embryos to 14 days, as this stage coincides with nervous system initiation in mice models.
For the first time, University of Cambridge researchers observed gastrulation in a human embryo aged approximately sixteen to nineteen days, donated by a woman terminating her pregnancy for scientific research.
Analyzing a sample of about 1,000 cells via single-cell RNA sequencing, the team identified gene activation patterns as cells specialized.
Results mirrored mouse gastrulation with key differences: human blood cell precursors emerged earlier, and crucially, no neurulation—the process establishing the central nervous system—had begun, unlike in mice where neurons form by the second week.
This rare glimpse into early human development challenges the 14-day embryo culture limit, potentially revolutionizing research and regenerative medicine.
Study details published in Nature.
