Establishing CUX1 as a determinant of Hematopoietic Stem cell heterogeneity - Project Summary/Abstract
Hematopoietic stem cells (HSCs) exhibit heterogeneity with respect to repopulating capacity, lineage bias,
and cell cycle participation. Teleologically, heterogeneity is the result of stem cells making fundamental
decisions regarding the population of the tissue. Differences in stem cell behavior have been linked to the
expression of cell surface and cytoplasmic markers without mechanistic explanation. HSC heterogeneity has
not previously been attributed to a transcription factor. We propose the observed heterogeneity in HSCs can
be explained by the actions of a dose-dependent, homeodomain-containing transcription factor, CUX1. Three
lines of evidence suggest CUX1 to be a putative orchestrator of HSC heterogeneity: it recurrently acts in a
dose-dependent manner across developmental systems, its recurrent loss in high-risk hematopoietic disease,
and its role in chromatin regulation.
I report the generation of a CUX1mCherry reporter mouse to study the role of CUX1 in hematopoiesis. The
Cux1mCherry mouse is the result of an in-frame, C-terminal mCherry tag at the endogenous CUX1 locus. The
addition of the tag creates no aberrant hematopoietic phenotype, suggesting this is a suitable model for the
proposed studies. The immunophenotypic long-term HSC (LT-HSC) compartment has among the greatest
variances in CUX1 expression. Across CUX1 protein levels in the LT-HSC compartment, we report several
correlations to strongly suggest that the observed variation in CUX1 protein results in meaningful differences in
stem cell behavior. For example, CUX1Bright HSCs are more likely to be cycling than CUX1Int and CUX1Dim
HSCs at steady state. Thus, our studies suggest that CUX1 is playing a dose-dependent role in murine
hematopoietic stem and progenitor cells (HSPCs). This proposal aims to (i) establish the role of CUX1 in
lineage bias and repopulating capacity and (ii) determine the mechanism by which CUX1 exerts a dose-
dependent role. Accomplishing the proposed studies will illuminate an important paradigm in developmental
biology: how a small pool of stem cells balance self-renewal and differentiation to give rise to all the mature
cells in a tissue. An etiological understanding of stem cell behavior will provide new insights into the
development of new therapies for the many diseases that arise in HSCs.
The project I propose here is accompanied by a training plan developed by me and my mentors that
delineates four goals I will need to accomplish to propel me towards becoming a successful independent
physician-scientist. These four goals include gaining expertise in hematopoiesis, gaining expertise in
bioinformatics, developing proficiency in scientific communication, and integrating the scientific and clinical
aspects of my training. Realizing these goals will give me the skills that I need to be a physician-scientist well-
equipped to address meaningful biological questions related to the catastrophic illnesses of childhood.
