Thrombopoietin signaling and a dedicated cytoskeleton regulate murine hematopoietic stem cell motility
During development, transplantation, and homeostasis, hematopoietic stem cells (HSCs) migrate to niches to (re)constitute and maintain the hematopoietic system. A solid mechanistic understanding of their movement is essential but remains poorly examined. Here, we used long-term single-cell imaging and tracking to quantify how motility changes as immature HSCs differentiate into multipotent progenitors (MPPs), establishing motility as an early indicator of differentiation. HSCs and early MPPs exhibit rapid, non-directional movement, while more differentiated MPPs move more slowly and directed. Interestingly, ex vivo expanded HSCs retain HSC characteristics with more non-directional movement, suggesting it as a defining HSC trait. Moreover, we show that movement phenotypes can identify cells with higher HSC potential in long-term cultures. HSCs feature a dedicated cytoskeletal architecture characterized by elevated expression of microtubule- and actin-regulating proteins, and by 3D imaging we show that this coincides with reduced cytoskeletal dynamics. FSCN1, a cytoskeletal regulator prevalent in immature cells, controls HSC locomotion by modulating cell shape, and influences cell cycle kinetics and HSC attributes. Finally, THPO, but not SCF or CXCL12, triggers HSC motility through PI3K/AKT signaling.