Project description:Stem cells (SC) exhibit a unique capacity for self-renewal in an undifferentiated state. It is unclear whether the self-renewal of pluripotent embryonic SC (ESC) and of tissue-specific adult SC such as hematopoietic SC (HSC) is controlled by common mechanisms. The deletion of transcription factor Zfx impaired the self-renewal but not the differentiation capacity of murine ESC; conversely, Zfx overexpression facilitated ESC self-renewal by opposing differentiation. Furthermore, Zfx deletion abolished the maintenance of adult bone marrow HSC, but did not affect erythromyeloid progenitors or fetal HSC. In both ESC and HSC, Zfx activated a common set of direct target genes. In addition, the loss of Zfx resulted in the induction of immediate-early and/or stress-inducible genes in both SC types but not in their differentiated progeny. These studies identify the first shared transcriptional regulator of ESC and HSC, suggesting a common molecular basis of self-renewal in embryonic and adult SC. Keywords: Global gene expression data analysis in Zfx-deficient murine ESC and HSC
Project description:Previously, we identified the transcription factor Zfx as a key regulator of self-renewal in murine ESCs. Here we extend those findings to human ESCs. Zfx knockdown in hESCs hindered clonal growth and decreased colony size after serial replating. Zfx overexpression enhanced clone formation, increased colony size and decreased expression of differentiation-related genes in human ESCs. Zfx-overexpressing hESCs resisted spontaneous differentiation but could be directed to differentiate into endodermal and neural cell fates when provided with the appropriate cues. Thus, Zfx acts as a molecular rheostat regulating the balance between self-renewal and differentiation in hESCs, revealing the close evolutionary conservation of the self-renewal mechanisms in murine and human ESCs. Human embryonic stem cells with over expression of ZFX were compared to the original cell line (H9) and a clonally derived wild-type cell line (clone 3)
Project description:Acute myeloid leukemia (AML) propagates as a cellular hierarchy which is maintained by a rare subpopulation of self-renewing leukemia-initiating cells (LICs). These LICs phenotypically resemble HSCs and early myeloid progenitors, and they are functionally defined by their ability to reconstitute AML in xenografted mice. Common transcriptional regulators are believed to drive self-renewal of LICs and normal stem cells. Examples include the histone methyltransferase, MLL and its main targets, the transcription factors HOXA9 and MEIS1; the polycomb group protein, BMI-1; and the Wnt/β-catenin signaling pathway4-9. In AML patients, LICs have been shown to share broad gene expression signatures with hematopoietic stem cells (HSCs) and, in some cases, with embryonic stem cells (ESCs). Moreover, increased expression of these stem cell signatures has been linked to tumor aggressiveness. Elucidating the molecular determinants of stem cell properties in LICs has the potential to improve AML therapy and clarify the relationship between cancer and stem cell biology in general. Here we show that the propagation of LICs in AML depends on Zfx, a transcription factor required for the self-renewal of ESCs and HSCs. Using mouse models, we found that Zfx is required for AML propagation and LIC maintenance. We defined a Zfx-driven gene expression program in murine LICs that correlates with existing stem cell-related gene expression signatures in AML patients. Using a novel, stroma-based RNAi screening strategy, we identified functionally important Zfx target genes. Two of these genes – FAM92A1 and DOCK7 - are required for human AML cell propagation; moreover, their expression levels strongly correlate with AML patient survival across the full spectrum of AML subtypes. Together, our results characterize a novel gene expression program that orchestrates critical stem cell properties of LICs, and drives aggressiveness of AML. Independent primary MLL-AF9 AML cell lines were created carrying the tamoxifen inducible Cre-ER transgene and either the Zfx wild-type (wt/y) (lines 10977, 10980) or the Zfx conditional (Zfx fl/y) allele (lines 10949, 10950, 10986). AML cells generated from each line were isolated from moribund mice and cultured with or without 4-hydroxytamoxifen for 72 hours to induce Cre. After Cre induction, c-Kit + cells were purified by FACS and processed for microarray studies.