Fluorescent proteins

Some of the most interesting things I get to work with in my lab are fluorescent proteins

Fluorescence occurs when a molecule absorbs light of one color (wavelength) and emits light of another color. For instance, you can shine ultraviolet light on certain rock
s like the ones below, and they’ll emit visible light of a lower wavelength.

It turns out that some organisms like jellyfish make proteins that are fluorescent. The most famous of these is green fluorescent protein (GFP). “How can a protein be fluorescent?” you might ask. The way that this works is that there are amino acids inside the protein that undergo a chemical reaction (shown below) to generate a fluorescent molecule or fluorophore. The amino acids within the protein have to be positioned next to each other in exactly the right way within the protein in order for this reaction to occur—it’s really an amazing chemical feat!

Here are some fluorescent jellyfish of the species Aequorea victoria

The GFP fluorophore absorbs blue light and then gives off green light. What makes all of this really useful for biologists like me is that scientists have been able to isolate and make copies of (“clone”) the gene that encodes green fluorescent protein. You can introduce the gene into other organisms and make them produce GFP and glow as well. Here are some GFP animals:

(Check out GFP Bunny and glowfish)

One way that this is useful for research is that you can place the GFP gene under the control of the promoter of another gene that you’re interested in. You can think of a promoter as a sort of biochemical switch that turns a gene on and off. The promoter of a gene regulates where (in which tissues and cell types) the gene is turned on or expressed. So if you put the GFP gene under the control of the promoter of another gene, you can see where that promoter is active in the organism. This promoter-GFP combo is an example of a “reporter gene.” It’s called that because it “reports” on where the promoter is active.

Here’s a really pretty example. This is an image of transgenic (“transgenic” means genetically engineered—with an added gene) fruit fly embryos and larvae in different stages of development. In these animals, the GFP gene is under the control of a promoter that is active only in motor neurons (the nerve cells that control muscles). And so the motor neurons glow and you can see them very clearly under a fluorescence microscope.

As you can probably imagine, there are many ways that this could be useful for biologists. It can not only show you where genes are active, but can also allow you to track different cell types by fluorescently labeling them. In fruit flies especially, there are some really awesome techniques that you can use to create patches of mutant tissue (known as somatic mosaic analysis). A GFP label allows you to distinguish mutant cells from normal (“wild type”) cells. I can talk more about that if anyone is interested…

Right now in my lab, I’m trying to create different fluorescent protein reporter genes to study the activity of different promoters. My ultimate goal is to develop a mathematical model of how those genes are regulated. My current model can be summarized with these equations:

(Don’t worry: You don’t have to understand all of that!)

My big challenge at the moment will be putting together an experiment to measure gene activity as a function of inputs and then use this data to fit and test the model. But more on all of this later!