CourtshipMackin' It Old School
Procreation, producing the next generation of one's species, is a fundamental drive for all living things. In order to convince a female fruit fly to mate with him, a male must successfully court her, a process consisting of a number of distinct activities carried out in a particular order. This complex behavior pattern is controlled to a great extent by a number of genes which have been identified by researchers, as well as a number that are still unknown.
The Drosophila gene fruitless (abbreviated fru) was discovered when researchers observed that flies which had mutations in the gene didn't produce any offspring. Different mutations have different specific effects, but all of them disrupt some aspect of normal male-female courtship. As a result, mating doesn't occur and (of course) no progeny are produced.
The product of the fru gene is a transcription factor, a protein that affects the "turning on" and "turning off" of many other genes. In addition, the fru gene product itself is extensively spliced: before it is used as a template for protein synthesis, the RNA made from the fru gene can be cut up and put back together in a variety of patterns. As a result, many different (but related) proteins can be made from a single gene.
In the figure at right, the three black boxes in the center are exons (the parts of the RNA transcript that are used for translation into protein) common to every fru transcript; versions which include the blue box alone (in the top line, second exon from the left) are expressed only in male fruit flies, whereas those which include the pink box (below it) are found only in female flies. As you can see, there are also forms which are made in both male and female flies, and several possible "endings" of any given transcript, shown on the right side.
Not all genes are alternatively spliced, especially to this degree: what's going on here? Why do organisms have genes that are alternatively spliced? One reason is because different versions of the gene's protein product are needed in different tissues or at different times during development. The expression of the male-specific transcripts of fru and another gene, doublesex, are responsible for the creation of a cluster of neurons called P1 which is present in the brains of male flies, but missing from the brains of female flies. How particular genes are spliced is critically important to determining whether a fly gets a male brain or a female brain (along with many other important decisions during development and later life).
Data from the modENCODE project are helping researchers determine patterns of expression -— what transcripts are expressed in which tissues during which developmental stages -— for fruitless and all the other genes in Drosophila. This, in turn, raises new questions and inspires new experiments to better understand complex genetic regulatory systems like this.
- Look at the second figure on the page, showing the fru transcripts. How many different fru transcripts are found only in males? How many are unique to females? How many different transcripts can this single gene produce all together?
- Have a look at the following videos showing Drosophila courtship:
Steps in courtship (set to music) (1:28)
Drosophila courtship (0:47)
You'll note that in the videos, the fruit flies are confined to a very small space, called a mating chamber. This isn't at all like their natural environment; why do scientists study mating in such artificial conditions?
More about fruitless
- Baker Lab Website
- Discussion of the Demir & Dickson paper