Abstract

Hematopoietic stem cells (HSC) maintain both a self-renewal capacity to persist throughout life and an ability to differentiate into mature cell lineages. HSC self-renewal programs are often ectopically activated in leukemia cells to sustain developmental arrest and neoplastic proliferation. Recently, the transcriptional regulator Bclaf1 (Bcl2 associated transcription factor 1) was shown to support proliferation and block differentiation of AML blasts. Bclaf1 is ubiquitously expressed in hematopoietic cells but its function in normal hematopoiesis has not been elucidated. Our data demonstrate that BCLAF1 promotes HSC development and function. To study the role of BCLAF1 in normal HSCs, we used murine models with constitutive deletion of BCLAF1 in hematopoietic cells (Vav Cre:Bclaf1f/f) or inducible global deletion (Mx-Cre:Bclaf1f/f). We find that Vav-Cre:Bclaf1f/f mice have normal fetal liver HSC numbers at embryonic day 14.5 (E14.5), but significantly reduced HSCs at embryonic day 17.5 (E17.5). This defect persists into adult bone marrow but does not exaggerate with age. However, induced deletion of BCLAF1 in adult Mx-Cre:Bclaf1f/f mice via treatment with poly(I:C) results in normal HSC numbers in the bone marrow. This data suggests that loss of BCLAF1 impairs HSC development but does not impair maintenance of homeostatic HSC populations. To examine the function of BCLAF1-deficient HSCs, we performed transplantation of 20 sorted LSK SLAM E17.5 fetal liver HSCs from Bclaf1f/f or Vav-Cre:Bclaf1f/f mice. Donors cells from Vav-Cre:Bclaf1f/f mice have significantly reduced multilineage repopulation capacity post-transplant. Transplantation of Vav-Cre:Bclaf1f/f adult bone marrow results in a similar defect in repopulation. Although loss of BCLAF1 in adult mice did not result in a reduction in HSC numbers, interestingly, 1:1 whole bone marrow transplants of Mx-Cre:Bclaf1f/f cells also resulted in a significant defect in HSC repopulation. These data demonstrate that BCLAF1 promotes normal HSC repopulation and self-renewal. We sought to characterize the mechanism by which BCLAF1 functions to promote HSC development and function. CITEseq of fetal Vav-Cre:Bclaf1f/f LSK cells reveals a reduction in long-term repopulating HSCs. Additionally, stress response genes are upregulated in BCLAF1-deficient LSK cells across all transcriptional clusters. CUT&RUN sequencing reveals that BCLAF1 associates with chromatin throughout the genome of fetal and adult hematopoietic cells, likely through indirect mechanisms, to regulate transcriptional programs. These results establish a novel function for the transcriptional regulator BCLAF1 in limiting stress responses in HSCs to preserve HSC development during embryogenesis and repopulation function after stem cell transplant.

Committee Chair

Jeffrey Bednarski

Committee Members

Grant Challen; Jeffrey Magee; Kyunghee Choi; Matthew Walter; Peggy Kendall

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Immunology)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

8-13-2025

Language

English (en)

Author's ORCID

https://orcid.org/0000-0002-6665-0108

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Available for download on Wednesday, August 12, 2026

Included in

Biology Commons

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