The placenta is a niche for hematopoietic stem cells

Area of Science:

• Developmental biology
• Hematopoiesis
• Stem cell research

Background:

• The hematopoietic system originates from specific embryonic sites.
• The precise anatomical origin and environmental regulation of definitive hematopoietic stem cells (HSCs) remain incompletely understood.
• Fetal hematopoietic microenvironments' roles in HSC development require further elucidation.

Purpose of the Study:

• To investigate the hematopoietic potential of the mouse placenta during embryogenesis.
• To determine the contribution of placental hematopoietic stem cells to the definitive hematopoietic system.
• To compare HSC populations in the placenta with other embryonic hematopoietic sites.

Main Methods:

• Embryonic stem cell analysis in mice.
• Hematopoietic stem cell (HSC) identification and quantification in placental, AGM, and fetal liver tissues.
• Temporal analysis of HSC emergence and expansion during mid-gestation.

Main Results:

• The mouse placenta functions as a significant hematopoietic organ during mid-gestation, housing a large pool of pluripotent HSCs.
• Placental HSC activity onset parallels the aorta-gonad-mesonephros (AGM) region, but the placental pool expands substantially (>15-fold more HSCs than AGM) until E12.5-E13.5.
• The expansion of placental HSCs (CD34(+)c-kit(+)) precedes and overlaps with initial fetal liver HSC expansion, and is not attributable to later-appearing circulating HSCs.

Conclusions:

• The placenta plays a crucial, previously underestimated role in the establishment of the mammalian definitive hematopoietic system.
• Placental hematopoietic stem cells represent a major source for fetal hematopoiesis.
• Understanding placental hematopoiesis is vital for comprehending embryonic blood development.