New Fluorescent Protein Permanently Marks Active Neurons

A new tool developed at the Howard Hughes Medical Institute’s Janelia Research Campus lets scientists shine a light on an animals’ brain to permanently mark neurons that are active at a particular time. The tool — a fluorescent protein called Campari — changes from green to red when calcium floods a nerve cell after the cell fires. The permanent mark frees scientists from the need to focus a microscope on the right cells at the right time to observe neuronal activity. “The most enabling thing about this technology may be that you don’t have to have your organism under a microscope during your experiment,” said a group leader and protein chemist at Janelia, who engineers tools to study the brain. “So we can now visualize neural activity in fly larvae crawling on a plate or fish swimming in a dish.” To make CaMPARI, the team started with a fluorescent protein called Eos. Eos emits a green fluorescence until it is exposed to violet light, which permanently alters the protein so that it fluoresces in red. Researchers spent more than a year tweaking their protein – making it brighter and more responsive to calcium and ensuring that it would work in cells and then in living mice, fruit flies, and zebrafish. In the end, they had a tool that they named CaMPARI, which stands for calcium-modulated photoactivatable ratiometric integrator. To read more about this study, click here.