Four years ago, Harvard scientists devised a way to make mouse neurons glow in a breathtaking array of colors, a technique dubbed “Brainbow.” This allowed scientists to trace neurons’ long arms, known as the dendrites and axons, through the brain with incredible ease, revealing a map of neuron connections.
Using a clever trick of genetic engineering, in which genes for three or more different fluorescent proteins were combined like paints to generate different hues, researchers created a system to make each neuron glow one of 100 different colors. The result was that the dendrites and axons of individual neurons, previously almost impossible to pick apart from their neighbors, could be traced through the mouse brain according to their color.
Now, fruit fly researchers have a similar bonanza on their hands. Last week, two Brainbow-based methods for making fly neurons glow customized colors—called dBrainbow and Flybow—were published in Nature Methods. This is the first time that scientists have converted the technique to work in fruit flies, and because these organisms have a very sophisticated set of existing genetic tools, researchers can exert even greater control over when and where the fluorescent proteins are expressed.
Because axons and dendrites are so long and fine, it’s hard to tell which neurons they are from. Researchers have traditionally had to stain just one or two neurons in each sample, painstakingly compiling data from many brains to build a map. In contrast, many neurons are easily discernible in this cross-section of a fly’s brain made using dBrainbow. Using dBrainbow images, Julie H. Simpson and colleagues at the Howard Hughes Medical Institute’s Janelia Farm could tell which motor neurons controlled parts of a fly’s proboscis, which it uses to take in food.