Gfi1 integrates progenitor versus granulocytic transcriptional programming

Area of Science:

• Hematology
• Molecular Biology
• Genetics

Background:

• Severe congenital neutropenia (SCN) and Gfi1 loss-of-function models exhibit myeloid progenitor accumulation and blocked terminal granulopoiesis.
• Previous assumptions suggested Gfi1-null progenitors accumulate due to impaired differentiation.

Purpose of the Study:

• To investigate the distinct transcriptional programs deregulated by Gfi1 loss of function.
• To elucidate the role of Gfi1 in regulating myeloid progenitor accumulation and terminal granulopoiesis.

Main Methods:

• Analysis of myeloid progenitor cells from SCN patients and Gfi1-deficient mice.
• Investigation of Gfi1's direct repression targets, including HoxA9, Pbx1, and Meis1.
• Assessment of progenitor transformation in collaboration with oncogenic K-Ras.
• Conditional allele analysis to determine the dose-dependent effects of HoxA9.

Main Results:

• Gfi1 loss of function deregulates two separate transcriptional programs: one controlling progenitor accumulation and lineage specification, and another affecting terminal granulopoiesis.
• Gfi1 directly represses HoxA9, Pbx1, and Meis1 during normal myelopoiesis.
• Gfi1-/- progenitors show elevated HoxA9, Pbx1, and Meis1 levels, leading to exaggerated HoxA9-Pbx1-Meis1 activity and progenitor transformation with K-Ras.
• Limiting HoxA9 alleles partially corrects Gfi1 loss-of-function phenotypes in myeloid progenitors but does not rescue blocked granulopoiesis.

Conclusions:

• Gfi1 plays a dual role in myeloid differentiation: suppressing the HoxA9-Pbx1-Meis1 progenitor program and inducing granulopoietic transcription.
• The findings clarify the molecular mechanisms underlying SCN and provide insights into myeloid development regulation.