The fruit fly Drosophila is a tiny laboratory where you can switch any gene on or off to figure out what it does. One such gene, EDTP, encodes an enzyme that strips phosphate tags off fat molecules inside the cell. It was once thought that this enzyme helps cells digest waste and that without it flies die before birth. But what happens when the enzyme is merely scarce rather than absent? The answer turned out to be unexpected.
Researchers took the DJ694 fly line, in which EDTP levels are reduced due to a random insertion in the gene. These flies developed normally but lived shorter and laid noticeably fewer eggs. The defect was recessive: a single copy of the normal gene completely rescued the situation. Males had a problem too: their sperm fertilized eggs less effectively, even though they mated more often than usual. When scientists put a working EDTP gene back into the same tissues, both lifespan and fertility were fully restored.
The most interesting part came when they checked the muscles. EDTP is known to participate in the process cells use to clear damaged proteins. It was logical to expect that a shortage of the enzyme would cause protein clumps to build up in muscles, just as they do in certain human diseases. But the DJ694 flies had healthy-looking muscles, moved normally, and no clumps accumulated. Yet in the eye, the same enzyme helped reduce the number of clumps. So the same protein works like different tools in different tissues: in the eye it is a janitor, while in muscles it is a traffic controller that does not clean up but oversees other processes.
This work shows that EDTP is critically important for adult fly life: without it, lifespan shrinks and the ability to leave offspring drops. But its role in muscles turned out to be unrelated to clearing protein waste, as previously thought. Perhaps the enzyme influences hormonal signals that control reproduction and aging. If we can figure out which fat molecules it processes in the ovaries and seminal ducts, that might suggest new ways to combat age-related infertility and muscle diseases. For now, one thing is clear: the same gene can be both a brake and a gas pedal depending on which cell it is working in.
The human homolog of EDTP was named hJumpy because of the jumpy behavior of flies with a mutation in this gene. DJ694 flies indeed show hyperactivity when startled and have trouble stopping their wing buzzing after landing.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.