GAL4/UAS in Drosophilia Melanogaster

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raincloud128
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GAL4/UAS in Drosophilia Melanogaster

Post by raincloud128 »

I am studying Parkinson's disease in fruit flies for my science project. I am interested in using the GAL4/UAS system, however all of the websites I go on only have confusing explanations. If anybody is familiar with these systems, could you please briefly explain to me in easy language how I can use it in a project on fruit flies? Thank you! :)
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Re: GAL4/UAS in Drosophilia Melanogaster

Post by SciB »

Hi,

I noticed that no one has answered your question, so I thought I would give it a shot. The Gal4/UAS system is a great way to visualize gene expression in a variety of organisms including fruit flies. As you said, it is a little hard to understand if you haven't had molecular biology.

The first thing you need to know is what the two acronyms, Gal4 and UAS, stand for. Both of them are proteins, which means they are encoded in genes in the DNA. They are actually from bread yeast, but they work the same way in Drosophila.

Gal4 is an activator of gene transcription, the synthesis of messenger RNA (mRNA) from DNA. The 'Gal' part comes from the name of a sugar, galactose. The Gal transcription factors were first discovered in yeast as the activators of galactose metabolism. You don't really need to know that but I put it in so you won't be wondering where the name comes from.

Transcription factors work by binding to a specific DNA sequence that is ahead [the correct term is 'upstream'] of a particular gene. When they are bound the gene can be transcribed and the resulting mRNA used to make the protein that is encoded by that gene.

The acronym UAS stands for 'upstream activation sequence', and guess what--that is the sequence Gal4 binds to!

OK. So what is Gal4 and the UAS good for? This is where it gets a little complicated so if you have more questions please post again. Molecular biologists who study the expression of specific genes, like for example some genes that are switched on or off in Parkinson's disease, want to have what is known as a reporter so they have a visual sign of when the gene is being transcribed. Most genes have an upstream sequence known as a promoter that sits right before the transcription start site and activates transcription.

What Drosophila researchers have done over the years is to create a bunch (probably in the 1000s by now) of mutant fruit flies that have the Gal4 gene placed downstream (towards the transcription start site) of the promoter of a certain gene that they are studying. It can be any gene. The Gal4 sequence is engineered into the Drosophila genome and when the flies reproduce, the offspring all have the Gal4 mutation in the same cells.

Now for the next part of the story. So, you have a fruit fly that has a Gal4 gene just after the promoter of the gene you are studying and you want to know when it is expressed. How do you do that? Remember that the Gal4 protein is itself an activator of gene transcription, but it needs its UAS to bind to in order to work. This is where the reporter comes in, and this is the complicated part, although once you get the concept it is rather simple and elegant.

A reporter is a gene for a protein that can be visualized in some way. A very common one is called green-fluorescent protein (GFP) and as its name tells you, it gives of a green glow when it is illuminated by light of a certain wavelength. If you google 'reporter genes' you can find out more about these important tools if you are interested.

The GFP gene actually came from a jellyfish so it is not normally found in Drosophila; but by putting the GFP gene under the control of a UAS, whenever Gal4 is produced, it will bind to the UAS, activate transcription of GFP and the cells in which it is present will glow green under a fluorescence microscope. That tells you that the promoter that was upstream of Gal4 in the study gene was activated. Now you are getting some information about what might control the expression of specific genes that might be associated with the onset or progression of Parkinson's disease.

This was a long explanation and I hope you understand now how Gal4/UAS is used as a gene reporter system. It is all done by molecular biology and genetic engineering and a lot of hours spent in the lab by a lot of dedicated scientists. Knowing which genes are expressed at which times in which cells is the most important thing in biology. Figuring out the sequence of the human genome was a great accomplishment, but the real job is to know how all those genes work in health and disease. Maybe you will be the one to discover a new gene expression system in Parkinson's disease that can be used to stop or prevent it.

If you still have questions, please don't hesitate to ask. That's what we are here for.

Sybee
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