HEMATOPOIETIC STEM-CELLS - CHALLENGES TO EXPECTATIONS

The past year provided a number of challenges to our expectations rega rding hematopoietic stem cell (HSC) biology. Evidence has emerged that HSCs arise intraembryonically before they can be detected in the yolk sac. A number of genes that may regulate the formation, self-renewal, or differentiation of HSC have been identified. New markers for purif ying HSCs have also been described. Although different groups have att ributed different properties to HSCs, it now appears that the differen ces may be explained by variations in assay conditions rather than by differences in the HSCs themselves. Finally, insights have emerged int o the complexity of the regulation of HSC proliferation and adhesion p roperties.