What the neuroscientists at Harvard University have accomplished could be described as vibrant and wonderful. And they call their system Brainbow. The technique forms the cover story of the November 1 issue of the journal Nature. To put it briefly, they created transgenic mice that were tailored to produce mixtures of fluorescent proteins in their neurons. They introduced the genes coding for 5 fluorescent proteins, each gene producing one fluorescent protein, into the genome of mouse embryonic stem cells. The transgenic mice were then developed from these stem cells. The fluorescent proteins expressed in the neurons were yellow, red, cyan, orange or red. The expression of these fluorescent proteins was controlled by the Cre/lox system in such a way that each neuron expressed only one of the fluorescent proteins predominantly. For example, a neuron expressing red and cyan protein would glow mauve; another expressing more of red and a little of green and blue would appear pink and likewise. The scientists were able to visualize more than 90 different shades produced by such differential expression of fluorescent genes in different neurons. It has been proposed that the technique would be very useful in studying the connections between neurons. Read the full article here.