Nature's new study answers the controversy: embryonic blood cells are not dependent on stem cells

The fetal liver is the main hematopoietic organ
at the embryonic stage.
It is generally believed that the hematopoietic grade of the fetal liver is established through the differentiation of fetal hematopoietic stem cells (HSCs
).
This view holds that the relationship between hematopoietic stem cells and progenitor cells of
the offspring is conserved from embryo to adulthood.
A collaborative study by Kumamoto University in Japan found that through lineage tracing and hematopoietic stem cell depletion of mutant mice, most hematopoietic progenitor cells came directly from precursor cells rather than hematopoietic stem cells
.
In addition, lineage tracking also showed that fetal hematopoietic stem cells have little effect on progenitor cells before birth
.
The researchers believe that most blood cells in embryos are not dependent on hematopoietic stem cells, prompting a reconsideration of the role of
stem cells in embryonic formation.

In terms of hematopoietic system formation, the researchers also solved a long-standing problem, namely the origin
of hematopoietic stem cells.

Previous transplantation experiments combined with in vitro culture have proposed that hematopoietic stem cells are mainly produced in the aorta-gonadis-midrenal region
of the embryo.
However, this finding has been controversial
due to the lack of clear molecules and molecular structures.
Now, for the first time, researchers have shown that the transcription factor Evi1 is specifically expressed in the intraembryonic arteries and that it is a necessary and sufficient condition for
hematopoietic stem cell production.

Until now, no method
has been established to specifically produce hematopoietic stem cells from iPS/ES cells.
Therefore, there is a need to have a clear understanding of the formation of hematopoietic stem cells and embryonic hematopoietic systems to promote the further development
of regenerative medicine.
The results of this study provide important evidence
for improving culture systems for clinically relevant hematopoietic stem cells.

"We know why hematopoietic stem cells are so difficult to produce," Dr.
Yokomizo said
.
"Our work suggests that the expression of Evi1 may be a good indicator
of inducing them in vitro.
"

Hematopoietic stem cells are important
in fighting many blood and immune diseases.
Dr.
Yokomizo and his team are trying to make it easier
to make hematopoietic stem cells for transplantation in the lab.
Currently, they are studying how hematopoietic stem cells are produced
before birth.

essay

Independent origins of fetal liver hematopoietic stem and progenitor cells