Summary: Scientists have developed a new understanding of how the first blood cells form during human development as they transition from endothelial cells to form blood cells of different types.
Scientists at Lund University, Sweden have developed a new understanding of how the first blood cells form during human embryogenesis as they show transition from endothelial cells to form blood cells of different types.
This is a first of its kind study showing the progression from an endothelial state, to a mixed endothelial/blood state to a blood only state. Using a laboratory model of human stem cell development, the expression of blood cell and endothelial cell genes in each individual cell was studied.
The understanding of how the first human blood cells develop would provide missing clues to generate blood stem cells in the laboratory for treatment of blood disorders and malignancies.
Hematopoiesis:
The blood passing through our veins is composed of billion of specialized cells that are responsible for many important functions such as providing oxygen to all tissues in our body and initiating immune responses against all infections including cancer cells. The first blood stem cells form during a very narrow period in embryonic development. These cells give rise to all types of blood cells. This process is known as endothelial to hematopoietic transition.
The cells that undergo transition to blood in the embryo start as endothelial cells that are components of arterial walls. During a short window period, a small number of tightly packed spindle shaped endothelial cells round up forming nascent blood. They are detached and released into circulation. In this process the cells undergoing transition show dramatic changes in their size and shape. (From spindle shape to round cells of the blood)
However, until now the exact molecular mechanisms had never been known. This new study reveals that cell populations showed differences in the repertoire of blood cell types that could be produced, which is a critically important finding in the origin of blood.
“Most cell types are believed to result from a linear sequence of undifferentiated stages, progressively restricting their potential until they are restricted to the mature state. Cells arising from a transitioning process may not need to follow this rule, giving wider flexibility to which blood cell types can be produced.”
This is a significant step towards understanding how the first blood cells are formed and how numbers and types of blood cells is regulated in development.