MYCT1 Controls Environmental Sensing in human Hematopoietic Stem Cells [scRNA-seq]

We identified a novel HSC regulatory gene, MYCT1 (MYC target 1), that is selectively expressed in undifferentiated human HSPC and is critical for human HSC expansion and engraftment. MYCT1 knockdown (KD) in human fetal liver and cord blood (CB) HSPCs impaired expansion ex vivo and engraftment after transplantation, whereas restoring the compromised MYCT1 expression via lentiviral overexpression (OE) in cultured human CB HSPCs improved ex vivo expansion of the most undifferentiated human HSPCs (CD34+CD38-CD90+CD45RA-EPCR+ITGA3+) and enhanced their engraftment ability. We performed single cell RNAseq of uncultured human CB HSPCs, as well as 72 hours after MYCT1 KD and OE to identify MYCT1-regulated programs in HSC and understand the role of MYCT1 in governing human HSPC expansion and engraftment ability. Functional enrichment analysis linked the loss of MYCT1 in HLF+ HSCs to a profound dysregulation of multiple cellular programs essential for HSC stemness, such as oxidative phosphorylation or proteostasis, while MYCT1 OE had the opposite effect and showed closer similarity to uncultured HLF+ HSCs. These data indicate that the loss or gain of MYCT1 expression elicits major effects on programs regulating human HSC functional competence.