Abstract
Transplantation of hematopoietic stem cells (HSCs) from human umbilical cord blood (hUCB) holds great promise for treating a broad spectrum of hematological disorders including cancer. However, the limited number of HSCs in a single hUCB unit restricts its widespread use. Although extensive efforts have led to multiple methods for ex vivo expansion of human HSCs by targeting single molecules or pathways, it remains unknown whether it is possible to simultaneously manipulate the large number of targets essential for stem cell self-renewal. Recent studies indicate that N6-methyladenosine (m6A) modulates the expression of a group of mRNAs critical for stem cell-fate determination by influencing their stability. Among several m6A readers, YTHDF2 is recognized as promoting targeted mRNA decay. However, the physiological functions of YTHDF2 in adult stem cells are unknown. Here we show that following the conditional knockout (KO) of mouse Ythdf2 the numbers of functional HSC were increased without skewing lineage differentiation or leading to hematopoietic malignancies. Furthermore, knockdown (KD) of human YTHDF2 led to more than a 10-fold increase in the ex vivo expansion of hUCB HSCs, a fivefold increase in colony-forming units (CFUs), and more than an eightfold increase in functional hUCB HSCs in the secondary serial of a limiting dilution transplantation assay. Mapping of m6A in RNAs from mouse hematopoietic stem and progenitor cells (HSPCs) as well as from hUCB HSCs revealed its enrichment in mRNAs encoding transcription factors critical for stem cell self-renewal. These m6A-marked mRNAs were recognized by Ythdf2 and underwent decay. In Ythdf2 KO HSPCs and YTHDF2 KD hUCB HSCs, these mRNAs were stabilized, facilitating HSC expansion. Knocking down one of YTHDF2′s key targets, Tal1 mRNA, partially rescued the phenotype. Our study provides the first demonstration of the function of YTHDF2 in adult stem cell maintenance and identifies its important role in regulating HSC ex vivo expansion by regulating the stability of multiple mRNAs critical for HSC self-renewal, thus identifying potential for future clinical applications.
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27 August 2018
In the initial published version of this article, there was an inadvertent omission from the Acknowledgements that this work was supported by Stowers Institute for Medical Research (SIMR-1004) and NIH National Cancer Institute grant to University of Kansas Cancer Center (P30 CA168524). This omission does not affect the description of the results or the conclusions of this work.
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Acknowledgements
We thank K. Tannen for proofreading and editing, and M. Hembree, H. Marshall, K. Zapien, D. Dukes, B. Lewis, A. Moran, M. Durnin, J. McCann, A. Box, J. Park, L. Holmes, J. Blank, and D. DeGraffenreid for technical support. We are grateful to X. Zhuang at University of Chicago for transferring the mice.
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Z.L. and P.Q. conceived the project, performed experiments, analyzed data, and wrote the manuscript. Z.L. conducted m6A-seq and irCLIP-seq. W.S. and J.Z. analyzed the m6A-seq and mRNA stability data. M.G., S.C., and H.L. analyzed irCLIP-seq and RNA-seq data. X.C.H. provided the training and performed the experiments. B.S., M.Q., Y.Z., and X.Z. generated the genetic mouse model. Z.Y., Y.W., J.P., F.T., K.Z., D.H., Y.H., C.Z., and H.X. performed experimental work. R.A., A.P., K.H., M.P., A.P., J.H., and T.P. provided technical assistance. S.H. and C.H. provided key suggestions and plasmids. L.L. supervised the study.
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Li, Z., Qian, P., Shao, W. et al. Suppression of m6A reader Ythdf2 promotes hematopoietic stem cell expansion. Cell Res 28, 904–917 (2018). https://doi.org/10.1038/s41422-018-0072-0
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DOI: https://doi.org/10.1038/s41422-018-0072-0
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