Mouse Hematopoietic Stem Cells, Unlike Human and Mouse Embryonic Stem Cells, Exhibit Checkpoint-Apoptosis Coupling

Previously, we reported that the spindle assembly checkpoint (SAC), which is coupled in somatic cells, is uncoupled from apoptosis-initiation in mouse and human embryonic stem cells (ESCs). This condition allows ESCs to tolerate and proliferate as polyploidy/aneuploid cells. Proper function of the SAC is vital to prevent polyploidy/aneuploidy during ex vivo hematopoietic stem cell (HSC) expansion. Here we address, for the first time, whether HSCs are more like ESCs or somatic cells with respect to SAC-apoptosis coupling. Using multi-parametric permeablized cell flow-cytometric analysis to identify and analyze the mouse sca 1(+)/c-kit(+)/lin(-) (LSK) population, we found the mitotic spindle checkpoint to be functional in primary murine LSK cells, a population enriched in primitive hematopoietic stem/progenitor cells, after prolonged activation of the SAC by microtubule-depolymerizing agents such as nocodazole. HSCs can efficiently initiate apoptosis after activation of the SAC in LSK cells as indicated by increased hypodiploidy and increased levels of activated caspase 3, suggesting that HSCs behave more like somatic cells instead of ESCs with respect to this important cell cycle checkpoint. We conclude that mouse HSCs are not subject to the same kinds of chromosomal instability as are ESCs, knowledge that might aid in optimizing in vitro culture and expansion of human bone marrow or cord blood HSC for clinical applications.