A role for thrombopoietin in hemangioblast development

Area of Science:

• * Hematology
• * Developmental Biology
• * Stem Cell Biology

Background:

• * Vascular endothelial growth factor (VEGF) and stem cell factor (SCF) are known growth factors for hemangioblasts.
• * Thrombopoietin (TPO) and its receptor c-Mpl regulate primitive hematopoietic stem cells.
• * The role of TPO in early hemangioblast development was previously unknown.

Purpose of the Study:

• * To investigate whether TPO influences hemangioblasts derived from in vitro embryonic stem cell differentiation.
• * To determine if TPO signaling plays a role in the earliest stages of hematopoietic development.

Main Methods:

• * Reverse transcriptase polymerase chain reaction (RT-PCR) to detect c-Mpl expression during embryoid body differentiation.
• * Hemangioblast colony-forming cell (BL-CFC) assays to assess TPO's effect on hemangioblast formation.
• * Secondary replating assays to confirm the nature of TPO-stimulated colonies.
• * Neutralizing anti-VEGF antibody experiments to assess TPO's independence from VEGF.

Main Results:

• * c-Mpl receptor expression was detected in early embryoid bodies coinciding with hemangioblast emergence.
• * TPO alone supported BL-CFC formation and significantly enhanced BL-CFC numbers when combined with VEGF and SCF.
• * TPO-stimulated BL-CFCs differentiated into both hematopoietic and endothelial lineages, confirming their hemangioblast identity.
• * TPO's enhancement of BL-CFC formation was independent of VEGF signaling.

Conclusions:

• * Mpl signaling is crucial for the earliest stages of hematopoietic development.
• * TPO acts as a novel growth factor influencing hemangioblast formation.
• * TPO plays a significant role in regulating primitive hematopoietic progenitor populations.