Mankind recently have known two rodent brains really very bright: one belongs to Ratatouille mouse by Pixar, the other one belongs to Jean Livet and colleagues from Harvard University
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Basically, a transgenic expressing Cre recombinase (induced by a ligand like tamoxifene), is mated with a transgenic in which a CMV/thy1 promoter express an array of 3 or 4 GFP reporters variants placed between different sets of incompatible lox sites. In each neuron (Thy1 promoter) of the progeny, Cre recombinase is forced to choose between two mutually exclusive excision events (lox). As a consequence of the random recombination event, a panel of neuron that massively express one, or two, or three different fluorescent proteins is generated. Finally, the signal of each GFP protein merges generating many different hues (at least 89). |
Now, the question is: which progress would bring that mouse to science? Why one scientist could be interested in tracking single neurons just in an anatomical context? The answer is in large-scale system biology: tracking each neuron (and possibly each connections that thousands of neurites belonging to a single neuron can develop), we could describe the "connectomic maps" of the brain (actually not completely rendered). But also lineage analysis could take advantage of such system, and why don't better explore brain development? What about probing individual regenerative events in spinal cord injury? The field of opportunities seems to me quite large considered that we are just dealing with an old reporter drived by a common CMV promoter. And, in case I'm wrong, rainbow mouse remains a memorial to the best GFP imaging ever. Listen the dedicated Nature Neuroscience Podcast here.
Update 2011. Brainbow fruit-flies (D. melanogaster) have been generated, read the news at Brainwindows.
2nd Update 2011. Other beautiful brainbow pictures freely available in a Cell Picture Show.
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Livet, J., Weissman, T., Kang, H., Draft, R., Lu, J., Bennis, R., Sanes, J., & Lichtman, J. (2007). Transgenic strategies for combinatorial expression of fluorescent proteins in the nervous system Nature, 450 (7166), 56-62 DOI: 10.1038/nature06293
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1 comments:
Obviously, limitations of the Cre/loxP system have not been an issue in the models used by the authors. However,one should keep in mind that Brainbow is dependent on the quality of the Cre lines employed. CreERT2 constructs tend to display background activity in the absence of the inductor. On the other hand in some models induction of high Cre activities may be disadvantageous too:
In the case of Brainbow 1 constructs that only rely on Cre mediated deletion high Cre activities confer all possible deletions resulting in a single color.
When Brainbow 2 constructs are used that allow multiple Cre mediated inversions colors of a single neuron may change if Cre activity is not tightly limited to a defined period. This may lead to coulor differences in the soma, dendrites and especially along the axon of an individual neuron.
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