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Characterization of hematopoietic progenitors from human yolk sacs and embryos
A Huyhn1, M Dommergues, B Izac
1INSERM Unit 362, Institut Gustave Roussy, Villejuif, France.
Insights
Early human development involves complex hematopoiesis originating in the yolk sac. Researchers identified distinct myeloid progenitor cells in human yolk sacs and embryos, revealing early hematopoietic stem cell plasticity and distribution patterns.
Area of Science:
- Developmental Biology
- Hematopoiesis
- Stem Cell Biology
Background:
- Hematopoiesis, the formation of blood cellular components, traditionally thought to originate solely from yolk sac stem cells seeding the fetal liver.
- Recent findings suggest multipotential stem cells in intraembryonic sites challenge the established model of early hematopoiesis.
- Understanding early hematopoiesis is crucial for comprehending the limitations of adult hematopoietic stem cell potential.
Purpose of the Study:
- To investigate the initial steps of hematopoiesis during human embryonic development.
- To characterize clonogenic myeloid progenitor cells in human yolk sacs and embryos (25-50 days gestation).
- To analyze the distribution and properties of early hematopoietic progenitors.
Main Methods:
- Characterization of clonogenic myeloid progenitor cells from human yolk sacs and embryos.
- Colony assays to assess progenitor cell potential and cytokine responses.
- Analysis of progenitor cell distribution within embryonic and extraembryonic tissues.
- Validation using CD34+ cells purified from yolk sacs and intraembryonic tissues.
Main Results:
- Yolk sac-derived erythroid colonies contained granulomacrophagic cells, indicating pluripotent progenitors with unique cytokine responses.
- A subset of non-erythroid progenitors generated large granulomacrophagic colonies, some yielding secondary erythroid colonies.
- Erythroid progenitors were equally distributed between yolk sac and embryo, while 80% of non-erythroid progenitors were embryonic.
- Significant numbers of non-erythroid progenitors, including high proliferative potential cells, were found in non-liver embryonic tissues.
Conclusions:
- Early human hematopoiesis is more complex than previously understood, involving distinct progenitor populations in both embryonic and extraembryonic sites.
- These early progenitors exhibit greater plasticity and different cytokine dependencies compared to adult hematopoietic stem cells.
- Findings provide insights into the developmental origins of hematopoietic stem cells and potential mechanisms for adult stem cell compartment restrictions.
Abstract:
Hematopoiesis first arises in the extraembryonic yolk sac, and it is generally believed that yolk sac-derived stem cells migrate and seed the fetal liver at approximately week 6 of development in humans. Recently, the identification at day 8.5 to 9 of multipotential stem cells in intraembryonic sites different from the liver suggests that the establishment of hematopoiesis might be more complex than initially believed. In an attempt to understand initial steps of hematopoiesis during human ontogeny, we characterized clonogenic myeloid progenitor cells in human yolk sacs and corresponding embryos at 25 to 50 days of development. Most erythroid colonies derived from the yolk sacs differed from adult marrow-derived progenitors in that they also contained cells of the granulomacrophagic lineage, suggesting that they were pluripotent and exhibited a different response to cytokines. Furthermore, a subclass of nonerythroid progenitors generated very large granulomacrophagic colonies, some of which generated secondary erythroid colonies on replating. Analysis of the distribution of progenitors revealed that in contrast to erythroid progenitors, whose numbers were equally distributed between the yolk sac and the embryo, 80% of the nonerythroid progenitors were found in the embryo at stages II and III. Interestingly, a high proportion of nonerythroid progenitors (including high proliferative potential cells) was present in colony assays initiated with cells remaining after the liver has been removed. These findings were validated in colony assays established with CD34+ cells purified from extraembryonic yolk sacs and intraembryonic tissues. Increased knowledge about the biology of hematopoietic stem cells early in life may help to further understanding of the mechanisms associated with the restriction in proliferative and differentiative potential observed in the adult hematopoietic stem cell compartment.