Tuesday, November 29, 2022
11/29/2022
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.
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