Abstract
The study of hematopoiesis has been a focus for developmental biologists for over 100 years. What started as a series of microscopic observations in different animal model systems has since evolved into studies of gene expression and regulation, and subsequent protein-protein interactions, cell surface protein expression profiling, and functional mapping of cell fates. In this review, we will discuss the milestone discoveries that have been achieved in the field of hematopoietic development, as well as the techniques that have been employed. Finally, we look toward the future and consider unresolved questions. We also reflect on one of the earliest realizations made in this area of study: that hematopoiesis is evolutionarily conserved, and as a consequence we reflect on the impacts of early and current discoveries and their clinical implications. The future direction of the study of hematopoietic stem cells will probably make use of pluripotent stem cells to yield specific immune cell lineages and eventual clinical applications.