Described herein are nucleic acid constructs, hematopoietic stem cell identifier animals, and methods of using thereof for isolating hematopoietic stem cell populations. Also provided are methods of using the identifier animals and cells isolated from them to screen for agents that affect the growth, proliferation, potency, expansion, or maintenance of the stem cells. Such agents can be used for promoting growth of stem cells in vitro or in vivo, and also for inhibiting cancer cells that have been determined to resemble a stem cell.
