Chinese Scientists Reveal Earlier Origins of Human Blood Cells

A team of Chinese researchers has unveiled the origin, differentiation pathways, and unique characteristics of primitive human haematopoiesis, filling a theoretical gap in understanding the developmental rules just before the onset of gastrulation. The research was conducted by scientists from the Institute of Hematology & Blood Diseases Hospital at the Chinese Academy of Medical Sciences (IHCAMS), the Beijing Institute of Technology (BIT), and the PLA General Hospital, with the results recently published online in the scientific journal Nature. Gastrulation is a critical stage in human embryonic development and one of the most mysterious and fascinating phases in life sciences. During this stage, the embryo transforms from a simple two-layered structure into a complex three-layered architecture, forming its body axis while undergoing multilineage differentiation and the formation of organ primordia. It was previously believed that blood cells only emerged after gastrulation. However, by studying rare early-stage human embryo samples, the research team discovered that human haematopoiesis begins much earlier than previously thought. Even before the formal start of gastrulation, the haematopoietic ‘factory’ in the embryonic yolk sac is already active, producing primitive erythrocytes, primitive megakaryocytes, and myeloid progenitors. Furthermore, the team constructed the first high-resolution spatial transcriptomic atlas for the pre-gastrulation stage. This research revealed that the earliest human blood cells do not originate from the epiblast, as long believed, but rather from extraembryonic mesoderm derived from the hypoblast. This finding settles a long-standing debate regarding the origin of early human haematopoietic cells. Additionally, the embryonic yolk sac is not a functionally uniform site for blood cell formation. It consists of two distinct ‘workshops’ differing in location and function: one primarily generates myeloid progenitors, while the other mainly produces primitive erythrocytes and megakaryocytes. Researcher Lan Yu from IHCAMS noted that this study not only transforms the understanding of early human haematopoiesis but also provides a physiological benchmark and new conceptual insights for fields such as de novo in vitro blood cell regeneration and the study of early human developmental disorders.