Biology and Biomedical Sciences: Molecular Cell Biology
Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
Timothy J Ley
Cold shock domain (CSD) proteins are the most evolutionarily conserved family of nucleic-acid binding proteins. There are four functional genes that contain CSDs in humans and mice: YBX1, MSY4, MSY2, and CSDE1. YBX1 is overexpressed in most cancers, and is frequently associated with poor outcomes and chemotherapy resistance. Both YBX1 and MSY4 are highly expressed in normal hematopoietic progenitors, and both are downregulated with terminal myeloid differentiation; both genes are highly expressed in virtually all cases of acute myeloid leukemia (AML). These two genes are functionally redundant as well: Msy4 has been shown to complement Ybx1 function in late-stage embryogenesis in mouse knockout models. Nevertheless, most studies that have sought to clarify the role of YBX1 in cancer have failed to consider a possible role for MSY4 complementation in cells where both genes are expressed. In mice deficient for either Ybx1 or Msy4, hematopoiesis is not altered. However, the loss of both proteins leads to a reduced ability for MLL-AF9 (a potent leukemia-initiating gene) expressing bone marrow cells to proliferate and serially replate in vitro, suggesting that Ybx1 and Msy4 have redundant functions in this model system. Since these proteins are involved in the prevention of senescence during proliferative stress, the inhibition of both proteins may provide a novel strategy for the treatment of AML and other cancers.
To create a system to study the roles of Ybx1 and Msy4 in the earliest stages of hematopoiesis (i.e. progression from pluripotency to committed hematopoietic stem cells), we developed a system to study the production of hematopoietic stem and progenitor cells from murine embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). By comparing the hematopoietic potentials of ESCs, and 24 independent iPSC clones obtained from a single adult mouse, we discovered considerable functional heterogeneity among the clones. To determine whether the basis of this heterogeneity was genetic, we sequenced the exomes of all 24 clones. Although each had a set of private mutations that defined its clonal origins, none of the mutations readily explained why some clones had a reduced potential to form hematopoietic progenitors in vitro. Finally, we compared the expression profiles of clones with extreme outlier phenotypes for hematopoiesis in vitro; this study yielded a small set of candidate genes (including Wt1 and Lef1) that could be relevant for the hematopoietic differentiation potential of mouse iPSCs. These findings have provided new insights into the origins of genetic heterogeneity among iPSC clones, and may ultimately provide new information about the genes that govern the earliest steps of hematopoietic commitment.
Li, Cheng, "Cold Shock Domain Proteins in Normal and Leukemic Hematopoiesis" (2014). All Theses and Dissertations (ETDs). 1247.