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This post was contributed by guest blogger Jon Chow, an immunology PhD student at Harvard University.

In my previous two posts, I’ve described the fundamentals of how to work with Drosophila as an experimental model organism. I then described the Gal4/UAS system used by geneticists to study gene function. In this final installment, I’ll provide a brief introduction as to how you can engineer new transgenic flies to study your favorite gene (YFG). 

This post was contributed by guest blogger Jon Chow, an immunology PhD student at Harvard University.

In this second post in our quick guide to working with Drosophila, you’ll learn how to maniupate expression of your favorite gene (YFG) in flies. Read the first post here.

Once you’ve identified some fly stocks and other reagents of interest, the next question to ask is what to do with them. In some cases, there might be a mutation that disrupts the function of YFG. You could compare this mutant fly to one lacking the mutation in the same genetic background. In other cases, YFG or one of its mutant variants will need to be overexpressed or knocked down. To do this, Drosophila geneticists use the Gal4/UAS system. This incredibly useful, yet simple system allows you to systematically study gene function with temporal control and cell-type specificity!

This post was contributed by guest blogger Jon Chow, an immunology PhD student at Harvard University.

Do you have a gene of interest but have run into a wall trying to study it? It happens. Is it an evolutionarily conserved gene? Can you find an ortholog in the Drosophila genome? Continue reading and I’ll show you how Drosophila can be used to push your research in new and exciting directions.

Drosophila are very easy to manipulate genetically and have limited genetic redundancy (meaning, there’s more of a chance of seeing a phenotype since additional genes that can do the same function are less likely to exist). If there’s an ortholog of your favorite gene (YFG) in Drosophila (and even if there’s not!) the wealth of Drosophila genetic tools available allow you to study many aspects of your gene’s functional biology in a living organism. This is the first post in a three-part series. We’ll first discuss how to get started on fly work in this post. The second post will detail a major tool used by Drosophila geneticists (the Gal4/UAS system), and the third post will describe how you can make your own mutant flies.

Find Drosophila Resources at Addgene

Cre-lox recombination is an incredibly useful molecular biology tool, but like any biological system, it has certain drawbacks. First, the efficiency of Cre recombination varies for different constructs and cell types. Second, Cre may induce recombination at pseudo- or cryptic loxP sites (estimated to occur at a frequency of 1.2 per megabase in mammals), leading to DNA damage and developmental aberrations. In multiple systems, Cre itself, without the presence of a floxed construct, may produce a phenotype. This problem is especially stark in Drosophila, where expression of Cre from the standard UAS/GAL4 system is toxic to proliferating cells. A Cre-estrogen receptor ligand binding domain-fusion can prevent this toxicity, but with the caveat of partial rather than complete recombination. If you’re looking to use site-specific recombination in Drosophila, read on to learn about new recombinases suitable for this system.

Gerald Rubin’s lab sought to make complex genome modifications in Drosophila using multiple recombinases. To make multiple, precise genome edits, the recombinases used must have high activity and specificity with low cross-reactivity, as well as low toxicity.