If you want to see where a particular gene is active, you can use green fluorescent protein, or GFP, and the cells will light up. If you want to turn that gene on or off in an organism, you might use an enzyme called Cre recombinase.

But if you want to turn a gene on or off only in one cell type? That’s hard.

But the job just got a lot easier. Harvard Medical School researchers have found a way to combine GFP and Cre.

The new tool, called “Cre dependent on GFP” or Cre-DOG for short, piggybacks Cre onto GFP so researchers can not only look at but also manipulate genes in GFP-expressing cells while leaving other cells alone.

Senior author Connie Cepko, Bullard Professor of Genetics and Neuroscience at HMS, said:

“In one step you can go from just looking at a cell to asking something about its physiology, its circuitry and its anatomy. That’s very powerful."

Doing More With Green Fluorescent Protein Lines

[caption id=“attachment_20209” align=“alignright” width=“300”]Aequorea victoria Structure of the ‘Aequorea victoria’ green fluorescent protein by Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute[/caption]

Over a thousand transgenic mouse lines have been engineered to express GFP in particular kinds of cells, while there are far fewer Cre lines. Cre-DOG allows researchers to skip the laborious creation of Cre lines by doing more with existing GFP lines.

“It opens up genetic manipulations in a much larger number of specific cell types and saves a huge amount of time and money,” said Cepko. “The more we know about how cells function, the better we can understand disease and development, allowing us to design more effective therapies."

Second author Stephanie Rudolph, a postdoctoral researcher in the lab of HMS neurobiologist Wade Regehr, said:

“In our lab we have a lot of mouse lines that express GFP, but so far, we only use them for anatomical studies. Now we can use them to study circuit function and development in the brain, define the roles of subpopulations of neurons within a circuit and study which neurotransmitters they release."

One perk of Cre-DOG is that the Cre-and-antibody molecules can be injected using adeno-associated viruses, or AAVs, a tool many researchers already use.

Jonathan C Y Tang, Stephanie Rudolph, Onkar S Dhande, Victoria E Abraira, Seungwon Choi, Sylvain W Lapan, Iain R Drew, Eugene Drokhlyansky, Andrew D Huberman, Wade G Regehr & Constance L Cepko Cell type–specific manipulation with GFP-dependent Cre recombinase Nature Neuroscience (2015) doi:10.1038/nn.4081

_Photo: GFP-expressing Purkinje cells in the brain turn red when Cre-DOG activates. Credit: Stephanie Rudolph _

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