Video: See first blood flow

What does it take for blood to start flowing for the first time in an embryo? That's the question that Atsuko Sehara-Fujisawa at Kyoto University and colleagues set out to answer by catching zebrafish blood vessels on film as they matured. The researchers saw that the blood cell precursors entered blood vessels and stayed there immobile, possibly tethered to the inner wall by adhesion molecules called PSGL1. It's not until an enzyme called ADAM8, a metalloprotease, is expressed by the blood cells -- cutting loose or weakening the tethering proteins -- that the blood begins to flow. See the blood cells (labeled with a red dye) as they start to flow within the blood vessel (green dye). A. Iida, et al., "Metalloprotease-Dependent Onset of Blood Circulation in Zebrafish," __Current Biology,__ 20:1-7, 2010, DOI 10.1016/j.cub.2010.04.052
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