Most proteomic analyses are averages of many cells. But as the sensitivity of mass spectrometry improves, comprehensive analysis of individual cells is becoming possible. By combining single-cell capillary electrophoresis, microflow electrospray ionization, and high-resolution mass spectrometry, Peter Nemes, Sally A. Moody, and Camille Lombard-Banek of George Washington University have performed proteomic analyses of individual cells dissected from a 16-cell frog embryo (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201510411). The researchers extracted and identified a total of 1,709 different proteins from three types of cells destined to develop into different parts of the frog’s body. To quantify proteins with high sensitivity, they used different mass tags to label each cell’s proteome, allowing them to detect even trace-level proteins at a low nanomolar concentration. Nearly a quarter of the proteins were common to all three cell types, but each cell type also had several hundred proteins unique to it. With the more direct measurements, the researchers were able to observe differences in protein expression that indicate dorsal-ventral asymmetry is already established, even at this early stage of development.