Brainbow Mice Soon to be Available From The Jackson Laboratory
JAX® NOTES Issue 508, Winter 2008
A primary obstacle that researchers have faced when attempting to map the neural circuitry of the brain (Sporns et al. 2005) has been their inability to clearly resolve the cellular elements involved. They have tried a number of approaches, from simple histological stains (developed generations ago) that allow them to distinguish small subsets of neurons to sophisticated array tomography (Micheva and Smith 2007). Still, they have so far been unable to develop a comprehensive, well-defined view of the brain's circuitry. Now, a promising tool has just been added to their toolbox: a set of fluorescent protein transgenic mice whose neurons have the potential to display every color of the rainbow.
Designed by postdoctoral fellow Dr. Jean Livet in the Harvard laboratory of Dr. Jeff Lichtman, the strains are described in a recent Nature publication as Brainbow transgenes (Livet et al. 2007).
The technology underlying Brainbow mice is deceptively simple. In Brainbow 1 type mice, the transgenic insert consists of tandomly arranged fluorescent protein genes separated by similarly oriented loxP and variant loxP sites. Transcription is driven by the neural/glial expressing Thy1 promoter (Caroni 1997). In the absence of Cre-induced recombination, the promoter expresses the fluorescent protein gene that is immediately adjacent to it. When Cre recombinase is present, the transgene undergoes one of several mutually exclusive excision events that positions a different fluorescent protein gene adjacent to the promoter, resulting in its expression.
Because the integration sites have multiple copies of the transgene, each neuron may express one of a wide variety of possible fluorescent protein combinations, and therefore emit a distinctive hue. Depending on the type of analysis used, over 89-166 colors may be distinguished.
Brainbow 2 type mice are similarly constructed, except that oppositely oriented loxP sites are introduced. As a result, depending on the Brainbow mouse line, Cre recombinase can induce excisions, inversions, or both. Inversions continue as long as Cre recombinase is present. Restricting cre activity to a limited time period stabilizes the transgene in a fixed configuration.
In designing the Brainbow transgenes, Dr. Livet tried to anticipate how researchers might use them. Hence, one of the proteins has membrane tethers allowing the axonal processes to be clearly labeled, another contains a nuclear localization signal, and yet another is distributed throughout the cytoplasm, allowing the neuronal cell bodies and dendrites to be more clearly labeled. In addition, a single FRT site at the 5' end of each transgene allows a user to reduce transgene copy number.
|
We are delighted to announce that the following 4 founder lines of Brainbow mice are under development at The Jackson Laboratory. You may express your interest in these strains at their respective strain data sheets. |
|
|
|
|
To maximize the number of colors displayed in labeled cells, Brainbow transgenics should be mated with cre-expressing mice. A wide selection of cre-expressing mice are available at The Jackson Laboratory. For more information, visit the web page for Cre-lox strains.
References
Caroni P. 1997. Overexpression of growth-associated proteins in the neurons of adult transgenic mice. J Neurosci Methods 71:3-9.
Livet J, Weissman TA, Kang H, Draft RW, Lu J, Bennis RA, Sanes JR, Lichtman JW. 2007. Transgenic strategies for combinatorial expression of fluorescent proteins in the nervous system. Nature 450:56-62.
Micheva KD, Smith SJ. 2007. Array tomography: a new tool for imaging the molecular architecture and ultrastructure of neural circuits. Neuron 55:25-36.
Sporns O, Tononi G, Kotter R. 2005. The human connectome: A structural description of the human brain. PLoS Comput Biol 1:245-251.
