ABSTRACT N6-methylation (m6A) is one of the most abundant endogenous modifications in eukaryotic mRNA. Accumulating evidence suggests that dynamic m6A RNA methylation has significant roles in multiple biological processes, and tumorigenesis by introducing another layer of post-transcriptional regulation of gene expression. Acute myeloid leukemia (AML), one of the most common types of acute leukemia, is a hematological malignant disease. In AML patients, gene mutations and genomic rearrangements often occur in hematopoietic stem/progenitor cells (HSPCs), and turn HSPCs into leukemia stem cells (LSCs), which play a central role in the development and maintenance of AML. To date, there is not an effective targeted therapy available for AML. The roles of m6A modification and its associated machinery in the pathogenesis of AML and the maintenance of LSCs/LICs remain elusive. As a nuclear m6A RNA reader that has been identified, YTHDC1 recognizes nuclear m6A-sites and acts as a critical mediator of nuclear m6A. YTHDC1 has unique roles in the regulation of nuclear RNA splicing, alternative polyadenylation, nuclear export and decay. However, its role and function in AML has not been reported yet. Our preliminary studies showed that YTHDC1 is overexpressed in human AML. We found that YTHDC1 is required for MLL-AF9-induced leukemogenesis and the survival of LSC/LIC. Thus, we hypothesize that YTHDC1 upregulation leads to post-transcriptional deregulation of a set of genes that are required for the maintenance of LSCs, thereby contributing to the pathogenesis of AML. In this proposal, we will determine 1) the role of YTHDC1 as a nuclear RNA reader in the initiation, development and maintenance of AML by regulating LSC self-renewal and survival; and 2) the underlying molecular mechanisms that mediate the role of YTHDC1 in the pathogenesis of AML. We will employ both genetic murine models as well as patient-derived xeno-transplantation (PDX) models to investigate the role of YTHDC1 in the pathogenesis of AML in vivo, and will combine transcriptome and epitranscriptome analysis to identify the key downstream targets and associated downstream pathways that mediate the role of YTHDC1 in leukemogenesis. In addition, we will elucidate molecular mechanisms by which YTHDC1 epigenetically controls the expression of its direct targets in AML cells. Our studies will define the unrecognized role of YTHDC1 in the AML development/maintenance and regulation of LSC/LIC self-renewal, quiescence and survival, and clarify the underlying mechanisms of YTHDC1. Thus, success of our project will provide new insights into the complicated mechanisms underlying epitranscriptomic regulation of leukemogenesis.