he Brainbow.The brainbow is a technique which allows individual neurons in the brain, or sections of the brain, to be mapped by giving them their own special fluorescent colour1 (see image to the right). It looks pretty, and the technique itself is deceivingly simple.
It takes advantage of something called the Cre/lox system. Cre is an enzyme (a recombinase, to be precise) which will cleave out any DNA that is flanked by sites in DNA with a particular sequence, "lox sites". So if you have Your Favourite Gene (YFG) sandwiched between two lox sites, then Cre will splice YFG out of the DNA. But what if you used two pairs of lox sites? For example, what if you constructed your DNA to look like this:
---loxA-loxB--Gene1--loxA--Gene2--loxB---If the loxA pair is cleaved, then Gene 1 is cut out; if the loxB pair is cleaved, then Gene 2 is cut out.
The scientists who developed the Brainbow realized that they could use this to make the neurons express one of many different fluorescent proteins. (See image to the left, taken from Nature2, click to embiggen) They used nestled lox sites as described
above, using multiple fluorescent proteins. The Cre protein is able to cleave a single lox pair, multiple pairs, or no pairs at all. The decision on which pair(s), if any, to cleave is made at random in each cell. What results is a cell that expresses a random colour. If enough colours or colour combinations are Incorporated into the construct, every neuron, in theory, will have its own randomly chosen fluorescent glow. This makes mapping the connections in the brain much easier than ever.And it makes for pretty artwork too.
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1. Transgenic strategies for combinatorial expression of fluorescent proteins in the nervous system, Nature, November 1, 2007.
2. Neuroscience: Making Connections, Nature, 457, 524-527 (2009)
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