Post-transcriptional regulation of hematopoietic stem cell function and cell fate determination during hematopoiesis

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Cell fate determination is a fundamental area in stem cell biology and critical to understanding the development and maintenance of functional organs. Hematopoiesis, the process of blood formation, is driven by hematopoietic stem cells (HSCs). HSCs are a small population of cells, which possess unique self-renewal ability to reconstitute all terminally differentiated cells in the system throughout a lifetime. During hematopoiesis, each step of cell fate determination is orchestrated and regulated by activation of a specific gene expression program, resulting in transcription of mRNAs and subsequently generation of functional proteins. However, little is known about how processes of protein synthesis i.e. post-transcriptional control impacts stem cell self-renewal and differentiation. After a native mRNA is made, it undergoes addition of a polyadenine (poly-A) tail, which helps protect mRNA from degradation and supports translation of mRNA to protein. PolyA deadenylation mediates the shortening of the poly(A) tail and starts the RNA decay process of mRNAs. The CCR4-NOT (CNOT) complex is one of two multi-subunit polyA deadenylation complexes. Recently, I discovered that RNA methylation m6A "writer" METTL3 is an important regulator of hematopoietic stem cells (HSCs) and translation. CNOT complex was recruited to m6A transcripts to mediate the mRNA degradation. Among all subunits of the CNOT complex, CNOT3 exhibits the highest expression in HSCs and is downregulated in progenitors and differentiated cells. Given central roles of the CNOT complex and the regulatory link between translation and mRNA decay, we aim to investigate a role for the CNOT complex, in particular CNOT3 in regulation of HSCs and hematopoiesis to uncover novel mechanisms underlying cell fate decision. The overarching goal of my research program is to determine post-transcriptional and translational mechanisms of gene expression regulation in control of HSC function and cell fate determination during normal hematopoiesis. Over the next 5 years, we will uncover the role of CNOT3 and the CCR4-NOT mediated deadenylation in HSCs and hematopoiesis. We hypothesize that control of mRNA decay and translation mediated by the CNOT complex is critical for cell fate determination in hematopoietic systems. Specifically, we propose 3 aims: AIM 1. Define the role of CNOT3 in normal hematopoiesis, AIM 2. Determine CNOT3 function in the regulation of HSC cell fate (i.e. HSC quiescence, cell cycle and control of asymmetric and symmetric division) AIM 3. Define the molecular mechanism for CNOT3 function in hematopoietic stem cells. These studies will identify novel mediators of blood cell maintenance and regeneration, as well as novel molecular mechanisms of mRNA degradation and translation cross-talk. The results will advance our knowledge in stem cell biology while providing insights to the elusive post-transcriptional research field.