The cortex of the mouse brain contains ~4,000,000 neurons, so investigating the complex connectivity of these neurons can be difficult.  Recently, this challenge has been overcome by creating transgenic mice that express fluorescent proteins of different colors in individual neurons in the brain.  In this “Brainbow” approach, Cre/lox recombination is used to randomly express two to four different fluorescent proteins in each neuron. The various combinations of fluorescent proteins can produce neurons of about 100 different colors. As a result, adjacent cells are usually different colors, allowing one to clearly visualize individual cells and their contacts with other cells.

The July issue of Cold Spring Harbor Protocols features an article by Jeff Lichtman, Joshua Sanes, and colleagues, who developed the Brainbow technique.  The article describes currently available Brainbow cassettes and transgenic mice, as well as the elements necessary for creating Brainbow transgenes from scratch.  An accompanying protocol provides step-by-step details for introducing Brainbow transgenes into mice, fixing samples from Brainbow animals, and acquiring and analyzing multichannel images from Brainbow samples.

The cover of the July issue shows motor neurons in the spinal cord of a young adult transgenic Brainbow mouse.  For more on the July issue, click here.