Thrombopoietin controls proliferation of embryonic multipotent hematopoietic progenitors

Area of Science:

• Hematopoiesis
• Developmental Biology
• Stem Cell Biology

Background:

• Thrombopoietin (TPO) is known to stimulate hematopoietic progenitor cells.
• The TPO receptor, Mpl, expression and function in early embryonic hematopoietic progenitor cells (MPPs) are not fully understood.

Purpose of the Study:

• To investigate Mpl expression in embryonic hematopoietic progenitor cells.
• To characterize the proliferative responses of early embryonic MPPs to TPO and other growth factors.
• To elucidate the signaling pathways involved in embryonic MPP proliferation.

Main Methods:

• Methylcellulose colony assays and liquid cultures were used to assess MPP proliferation.
• Expression of Mpl was examined in embryonic cell populations.
• Inhibition of JAK2 and manipulation of STAT5 were employed to study signaling pathways.

Main Results:

• MPPs in the c-Kit(+) population of mouse embryos express Mpl.
• Early embryonic MPPs from yolk sac and embryo proper proliferate with TPO and SCF, and are maintained by TPO alone.
• Fetal liver MPPs show intermediate proliferative activity, suggesting a developmental switch.
• JAK2 inhibition suppressed proliferation, and activated STAT5 could substitute for TPO, indicating their roles in signaling.

Conclusions:

• Early embryonic MPPs exhibit distinct proliferative responses compared to adult bone marrow MPPs.
• A developmental transition from embryonic to adult MPP characteristics occurs within the embryo.
• The JAK2/STAT5 pathway is crucial for mediating TPO-driven proliferation in early embryonic MPPs.