There are a multitude of signals that elegantly orchestrate the proper development of the heart. In this image of a 3-day-old zebrafish heart, the signal that is localized to the developing atrio-ventricular valve and smooth muscle is labeled in green using green fluorescent protein (GFP). This particular signal is important for the formation of the cardiac valves, which will allow blood to pass from the ventricle (right) to the atrium (left), both in orange, in the adult zebrafish. The blue stain DAPI labels the nuclei in all the surrounding cells.

Contributed by Michka Sharpe, a fifth year graduate student in the Biological and Biomedical Sciences program at Harvard Medical School, and our Featured Artist for August 2017.