Hearts grow with the flow

Aproperly formed heart comes only after effort—the pumping of cells through a primitive heart to generate gene-activating shear forces. That is the conclusion of Jay Hove, Reinhard Köster, Scott Fraser, Morteza Gharib, and colleagues (California Institute of Technology, Pasadena, CA), who have come up with a method for watching heart development by culturing developing zebrafish on microscope stages.

The researchers tracked the movement of blood cells against the background of fluorescently stained blood serum. High-speed imaging (1,000 frames/s) and digital particle-tracking yielded movement vectors for the blood cells. The cells moved at speeds of up to 1.5 mm/s in a primitive, valveless heart and 0.5 cm/s in a more developed heart. The resultant churning forces should be more than enough to activate the many endothelial genes known to respond to shear stress.

The high...