The Princeton team used confocal microscopy to visualize the spatial distribution of two proteins that compete for the MAPK enzyme in early fruit fly embryos. In areas where levels of a protein important for the development of the head were high (shown here in red, with brighter color indicating the presence of more protein) there was less enzyme available to act upon a different protein (shown here in green) that is important for the development of the ends of the embryo, including the tail.

Images: Shvartsman Lab