The Hematopoietic System

Current understanding of the hematopoietic system draws heavily from clinical observations and research in humans and mice. Numerous gene-deleted mice targeting transcription factors, hematopoietic cytokines and their receptors, and extracellular matrix components and their receptors are central to our knowledge of hematopoiesis at the molecular level. Recent studies have contributed information about the critical role of the bone marrow microenvironment. Hematopoiesis is the cumulative result of intricately regulated signaling pathways mediated by soluble cytokines and their receptors. Evaluation of cytokine–receptor interactions in hematopoiesis has largely been achieved through creation of gene-deleted mice and conditional knockout mice, the phenotypes of which range from severe lethal embryonic, fetal, and neonatal defects to redundant null phenotypes. The specificity of hematopoietic cytokines is determined by progenitor and precursor cell expression of their cognate receptors.