Glowing Cells
In the mid-1990s, researchers began marking specific cells in lab animals by genetically engineering the organisms to incorporate fluorescent proteins (above) found in marine species. Within 10 years, these proteins had been engineered into the cells in more complex ways, enabling researchers to monitor biochemical reactions and track the movements of cellular proteins in real time.

Credit: Koki Moriyoshi et al., Neuron, February 1996