Hematopoietic stem cell division is governed by distinct RUNX1 binding partners

Area of Science:

• Hematology
• Stem Cell Biology
• Molecular Biology

Background:

• Hematopoietic stem cells (HSCs) self-renewal and differentiation maintain lifelong blood production.
• Transcription factor networks, including RUNX1, regulate HSC fate and clonal diversity.
• RUNX1 mutations can decrease hematopoietic stem cell clonal diversity.

Purpose of the Study:

• To identify modulators of RUNX1 and HSC expansion.
• To elucidate the mechanism of the RUNX1 inhibitor Ro5-3335.
• To investigate the potential for pharmacological enhancement of stem cell clonal diversity.

Main Methods:

• Chemical screening in zebrafish to identify HSC expansion modulators.
• Transplantation assays in zebrafish to assess chimerism.
• Studies using human CD34+ cells to analyze the effect of Ro5-3335 on the RUNX1 transcription complex.

Main Results:

• Ro5-3335 increased HSC divisions in zebrafish, leading to enhanced chimerism after transplantation.
• Ro5-3335 remodels the RUNX1 transcription complex by binding to ELF1, independent of CBFý.
• This interaction promotes the expression of cell cycle genes, enhancing HSC self-renewal and preventing differentiation.

Conclusions:

• Ro5-3335 pharmacologically increases the number of stem cell clones in vivo, demonstrating a novel mechanism for enhancing clonal diversity.
• RUNX1 binding partners, specifically ELF transcription factors, play a critical role in guiding cell division and determining cell fate.
• This research opens avenues for developing treatments to enhance clonal diversity for various blood diseases.