SDF-1 directs megakaryocyte relocation.

In this issue of , Niswander et al answer the questions: (1) Does stromal cell-derived factor 1 (SDF-1) direct megakaryocyte spatial distribution in the bone marrow? and (2) What effect does local SDF-1 concentration have on platelet output? If José Arcadio Buendía in had followed SDF-1, as megakaryocytes do, perhaps he would not have wandered the jungle for so long before founding Macondo at the riverside. Although we may never know what drew José Buendía to his city at the water's edge, megakaryocytes (parent cells to circulating blood platelets) appear to follow a chemotactic SDF-1 gradient as they migrate through the bone marrow endosteum to rest adjacent to sinusoidal blood vessels. There, they extend and sequentially release platelets, and larger preplatelet/proplatelet intermediates into the circulating blood. Although the physiological triggers governing platelet production from megakaryocytes are still being resolved, it is certain that without direct access to the bloodstream, megakaryocytes cannot produce the roughly 1000 to 2000 individual platelets that are so critical to clot formation and blood vessel repair.