The earliest haematopoietic precursors that can give rise to both haematopoietic and endothelial cells. A marker, flk-1 (vascular endothelial growth factor receptor), is first observed in the human embryo at the beginning of week 4. Early haematopoiesis from primitive haemangioblasts in the extraembryonic mesoderm of the yolk sac generates mostly erythroid and some myeloid lineages, whereas the later definitive haemangioblasts from intraembryonic mesoderm give rise to a wider range of cells including cells of the lymphoid series. It is not clear for mammals whether definitive haemangioblasts develop by maturation of primitive haemangioblasts, or arise from a separate mesodermal cell population, or from a combination of both. Lindau's tumour is a haemangioblastoma.
Subjects: Medicine and Health.