An expanded 'Brainbow' tool kit for fluorescently labelling cells in mice
The complexity of the brain and other organs makes identifying the connections among individual cells a daunting challenge. The development of “Brainbow” technology has enabled great advances in imaging by exploiting the Cre/lox system to randomly assign each cell a unique combination of red, yellow and blue fluorescent proteins (Livet et al. 2007). The system works in a similar way as cathode ray tubes, which combine red, green and blue light to generate the full spectrum of colors on a TV screen. Recently developed Brainbow mice from the laboratory of Joshua Sanes at Harvard expand the toolkit with better strains to study how neurons interrelate (Cai et al. 2013), while other related strains bring Brainbow technology to the entire mouse (Snippert et al. 2010; Tabansky et al. 2013).
The new Brainbow lines (called Brainbow 3.1 and 3.2) offer several advantages over the original Brainbow models:
- Unlike the original strains, there is no fluorescence before Cre recombination that might complicate the imaging.
- Targeting the fluorescent proteins to membranes allows better visualization of neuronal processes and dendritic spines.
- Fluorescence is brighter, especially in the Brainbow 3.2 mice.
The Jackson Laboratory distributes two different Brainbow 3.1 strains, STOCK Tg(Thy1-Brainbow3.1)3Jrs/J (021225) and STOCK Tg(Thy1-Brainbow3.1)18Jrs/J (021226), that target many types of neurons . A Brainbow 3.2 strain, with enhanced fluorescent protein expression, is available as STOCK Tg(Thy1-Brainbow3.2)7Jrs/J (021227).
Brainbow is not just for brains anymore. The technology has been adapted for general use anywhere in the mouse. Strains such as "Confetti," B6.129P2-Gt(ROSA)26Sortm1(CAG-Brainbow2.1)Cle/J (017492), carry an insertion of a Brainbow transgene in the Rosa26 locus that is expressed throughout the entire mouse (Snippert et al. 2010). Single cells can now be labeled in virtually any tissue type by mating Confetti mice to Cre transgenic mice that target specific tissues. Confetti mice have been used to understand how stem cells divide in the intestines, lung, bone marrow and other tissues. B6(D2)-Tg(CAG-Brainbow1.0)2Eggn/J (021011) is a similar strain that uses the actin promoter to label cells anywhere in the mouse with one of up to 21 different colors following Cre recombination (Tabansky, et al. 2013).
The expanded Brainbow toolkit now contains a diverse set of strains for imaging different tissues throughout the mouse and to support dissection of complex cellular functions and architectures.