It’s a Brainbow!

Is it just me, or are papers that utilize fluorescent proteins actually extra badass? 

This particular work by Livet et al. was published in Nature in 2007 (for citation, see below). The idea was to come up with a method that allows you to produce connectivity maps in order to analyze neuronal network architecture. One possible way of doing this was proposed by Livet and colleagues. They cloned three or four different fluorescent protein genes into mice, which were expressed on the cell membranes. This only yields limited colors, however, so the researchers also used the Cre/lox recombination system. Cre is a DNA sequence specific recombinase, which splices the DNA at loxP sites.

Via strategic placement of lox sites,some of which were incompatible with one another, Livet et al. forced the Cre recombinase to “choose” one of several mutually exclusive excisions. Only one excision can occur because excision of one pair of identical lox sites removes one site of the second pair, preventing additional recombination. (Confusing, I know. See Figure 1a in their paper! Or below.)

So, via recombination of these fluorescent protein genes, each neuron expresses a different set of fluorescent proteins on its membrane. Okay, okay, not *each* neuron. Livet et al. found that combinatorial expression of three different fluorescent proteins yielded about 90 colors in neurons, which they think will allow mapping of neuronal circuits. They demonstrated this technique in neurons and glial cells.

Pretty cool right? PICTURE TIME:

Sorry, I couldn’t get a higher resolution one :( Additional, better pictures can be seen here.

Livet, J.; Weissman, T. A.; Kang, H.; Draft, R. W.; Lu, J.; Bennis, R. A.; Sanes, J. R.; Lichtman, J. W., Transgenic strategies for combinatorial expression of fluorescent proteins in the nervous system. Nature 2007, 450 (7166), 56-62.

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