So in our nervous system, in the neurons, besides the Golgi staining, we are still using Golgi staining, even up-to-date. But besides this staining, we have many more methods to study, to label neurons, and then to study the neurons and other cells in our system. One very useful labeling method is to label cells, special groups of neurons, with fluorescence protein, like the example here in these three pictures. 3 We can label a certain group of cells, neurons, with green fluorescence protein. Or, with two colors, with green colors or the other with red colors, so we can distinct different group of cells or neurons, or we can label neurons or cells with visible color or visible light, like the example showing here. So talking about the fluorescence protein, that's a nice story in biological discovery history. So green fluorescent protein, sometimes it can be shortened as a GFP, was first discovered in 1920s by a Japanese scientist, Osamu Shimomura. And he discovered this protein in Woods Hole labs by studying this particular ocean animal that has the auto fluorescent protein. And then he, it was the first time to isolate this protein in the jellyfish. And then later on, many of you may hear about this famous, Roger Tsien. He actually finished the last step of GFP, green fluorescence protein, developed from it. And for the first time, Shimomura discovered this protein as green or bluish color and Roger developed the so many colors of these fluorescence protein, he can turn this green fluorescent protein into blue, red, pink, yellow and other colors that you can label several proteins or several things at one time. And then he developed some other criterions of this fluorescence protein, that you can turn it on or turn it off by laser or by heat. You can turn it on by pH changes or alterations in the cellular compartment or the solution. So, to study a protein in the cells, fluorescence protein now is a very critical tool for us to study protein function in the cells. Because, if you want to look at a protein where it is and where is expressed is almost impossible because protein is invisible. It's invisible in the cells, so if we label a protein with some visible thing, with the color, fluorescent color, then we can track the route that this protein go along the way. And then we can track where and how this protein get synthesized, and expressed. It's just like a man with a dark dress and walking at night, you can't see him at all, and if this man is carrying a lantern or a lamp, then you can track his route and where he appears and where he disappears. Roger Tsien, he studied about chemistry in UCSD, and then because his famous discovery on fluorescence protein, he won this Wolf Prize in medicine in 2004. And then these are the fancy pictures that we can make nowadays with the extraction of this fluorescent protein. This is just a bacterial plate, grown with a different strain of bacteria that can express different color of fluorescence protein. Let's say, these bacteria, they express green in color and then these ones are expressed in red color and then these ones with blue color that you can kind of like draw this picture and then, this is a labeling in our brain. Tissues that with different colors of this fluorescence protein, we can, not only label neurons, like the cells here, we can also label other cell type, like astrocytes, or glia cells, down here, a series variations or variety of fluorescence protein. So this is the structure of fluorescence protein, it's barrel, like protein, so within the color or the light that produce the bio-fluorescence, we make it visible, it's located within this barrel shape channel here. So because of their great achievement in discovering and the application of fluorescence protein, Shimomura, Martin Chalfie, and Roger Tsien, three of them won the Nobel Prize in 2008. And then this is a sculpture showing you the structure of this green fluorescent protein.