// ARS TECHNICA — FINANZA
Fruit flies remember their larval diet, which influences their longevity
Eating less protein as larvae may limit their ability to produce proteins as adults.
Back in the 1930s, scientists noticed that water fleas and rats fed restricted diets while young went on to live longer. The same effect has since turned up in fruit flies and mice. What we did not know was how a meal eaten in infancy could affect health weeks, months, or even years later. A recent Nature study might have found the answer.
A team led by Fumiaki Obata, a biologist at the RIKEN Center for Biosystems Dynamics Research in Kobe, Japan, found a protein that carries a record into adulthood of what fruit flies ate as larvae, influencing how long they live.
Lab fruit flies are fed a mix of yeast and sugar, with yeast being their main source of protein. “We decreased only the yeast concentration in the diet, from eight percent to either one or two percent,” Obata explains. This low-protein diet was introduced roughly halfway through the larval period. Once the flies emerged from their pupae as adults, they returned to standard food.
In Obata’s experiment, the protein-restricted flies, males and females alike, outlived their well-fed siblings. But it came at a cost. The flies were paler and lighter, weighing sometimes 28 percent less. The females also laid fewer eggs.
“It’s very common, actually. Reproduction and lifespan are always in a trade-off relationship,” Obata says. “This is also the case in this early-life dietary restriction. They have fewer eggs and they are slightly smaller. But they have a lifespan extension.”
This typical trade-off wasn’t the whole story, though. When the team added amino acids, the building blocks of proteins, back into the low-yeast larval food, the lifespan boost disappeared. Somehow, the adult flies’ bodies were remembering how much protein they had eaten as larvae. Obata and his colleagues called this a nutritional memory and set out to find where exactly in the body that memory was kept.
Comparing gene activity in adult flies raised on low-protein and standard diets turned up around 100 candidate proteins that could store the information about early protein intake. “We basically went one by one, checking which would be important,” Obata says.
To narrow the search down, the team tagged the larval food to tell which proteins in an adult fly’s body were built from food it ate as a larva. Larvae were raised on a synthetic diet in which two amino acids, lysine and arginine, were made with rarer, heavier isotopes of carbon and nitrogen atoms. Once the larvae became adult flies, the team switched to food with a second set of amino acids tagged with different, lighter isotopes.
Then the researchers used mass spectrometry to weigh fragments of proteins from the flies’ heads. The same protein fragment might register as a few units heavier or lighter, depending on whether it was built from larval or adult food. “This is basically only achievable with this stable isotope experiment,” Obata says.