Science Sunday: Brainbows part 1 or, the magic of fluorescence
ScienceSunday (see here) brings you great science posts every Sunday on Google+. We wanted to join in! So here’s our first post, and we’ll have more to look forward to each week.
One of the coolest biotechnological tricks I learned about in class is the imaging technique that’s been dubbed the “brainbow.” However, there’s a lot of background I should go into before actually getting to the brainbow–and why it’s so cool–so today I’ll be doing a little review about the magic of fluorescent proteins.
For years, biologists have been exploiting new advances in genetics and cell biology to express fluorescent proteins in the cells they want to image. Green fluorescent protein (GFP) was the first, and is still the most widely used for a variety of applications. The scientists who discovered and tweaked GFP to a broad range of uses were actually awarded the Nobel Prize in Chemistry in 2008. (A bit of good history, for those who want it, is here.) Since the discovery of GFP, various mutations have yielded proteins in other colors, such as CFP (cyan fluorescent protein) and YFP (yellow fluorescent protein).
Here are some examples of images that use fluorescent proteins to tag certain cells. Once the protein is expressed in the cell, the researcher can take a sample of the tissue and shine various lights or lasers on it to get the protein to fluoresce. When it does, the color pops out–and rather strikingly, too.
In this recent paper by Fatima (2011), GFP is being expressed in the actin in the sperm head of a fruit fly (Drosophila). The sperm tails are clearly bent, causing malformations and leading to sterility.
In this paper, Feng and colleagues tagged a gene, thy1, that is expressed in many parts of the nervous system, with a few GFP variants. Here you can see that it is expressed in neurons in the hippocampus.
One of the most amazing things about fluorescence imaging with these proteins is that biologists are able to see cell morphologies that they could never have seen before. By tacking GFP onto a specific gene, they are not just making the entire organism light up with green and yellow colors–they are only imaging that one specific protein. This has enabled us to track where specific proteins are made, where they finally go, and how much of them are expressed. They can essentially visualize gene expression. I don’t think I can overemphasize how nuts this is. This has helped us unravel many different questions about gene functions in many areas of research, from fruit fly reproduction to memory in the mouse hippocampus to a variety of cancers in many model organisms.
Previous cell visualization techniques–essentially using simple chemical stains–were not very specific. Using genetic techniques and GFP, researchers suddenly have enormous control over what is visualized. Next week we’ll finally get to the brainbow, which uses a variety of different fluorescent proteins (now they’re just XFPs) to trace different cell lines over time. Trust me, it’s gonna be awesome!
Featured image credit: From this page on GFP. Roger Tsien shared the Nobel Prize in Chemistry in 2008 with Osamu Shimomura and Martin Chalfie for their discovery and development of GFP.