Google ‘royal jelly’ – the goo that sustains honeybees destined for royalty – and the first hits tout its benefits: from youthful skin to virility to an anxiety treatment. These dubious perks are aimed at humans, but other organisms may want to take notice.
A new paper published online today in Nature identifies a key component of royal jelly and finds that it endows female flies with some of the physical traits of queen bees, by acting on the same cellular pathways.
“Finding the active components of royal jelly that are important for queen development has been kind of a holy grail of insect research for decades,” says Gro Amdam, an entomologist at Arizona State University in Tempe, who was not involved in the new paper.
All newly hatched honeybee larvae gorge on the heady mix of proteins, fats, sugars and vitamins. After three days, though, soon-to-be worker bees switch to a diet of honey, pollen and water, while the heirs to throne continue to eat royal jelly. This shift underpins the eusocial lifestyle of honeybees, in which sterile workers support a hyper-fertile queen, who grows much larger and lives about 20 times longer than workers.
Research from the 1960s suggested that royal jelly contained a potent neurochemical, while a 1972 paper highlighted developmental hormones. More recently, scientists identified a set of Major Royal Jelly Proteins, potentially involved in making queens.
On the hunch that one of these proteins might be a key ingredient of royal jelly, Masaki Kamakura, an entomologist at the Biotechnology Research Center in Toyoma, Japan, designed a simple experiment.
He stored royal jelly at a temperature that degraded its proteins at different rates and then he tested whether the heat-treated jelly could still make queens. It took 30 days for the potency of royal jelly to vanish. Chemical analysis showed that a protein he had previously named royalactin was one of the slowest to break down but was gone by 30 days.
The royalactin protein, when combined with other nutrients, transformed larvae into queens just as effectively as royal jelly.
To get a better handle on how royalctin could make a queen, Kamakura tested the protein on fruit flies. Although the common ancestor of fruit flies and honeybees lived tens of millions of years ago, the two share enough in common that royalactin might affect the same cell functions in them. Also, geneticists have created thousands of fruit fly strains that lack particular genes, which could steer Kamakura to those influenced by royal jelly.
Fruit flies fed royal jelly or royalactin (shown below) gained some of the traits of queen bees. They grew larger, more fertile and lived longer than flies on a normal diet.
Meanwhile, mutant flies hinted that royalactin was recognized by a protein called EGFR, which senses hormones called epidermal growth factors. Flies lacking EGFR or some of the proteins it communicates with got none of the growth or fertility benefits of royal jelly or royalactin, Kamakura found. Reducing the levels of the growth factor-sensing protein in honey bee larvae, meanwhile, prevented royal jelly-fed larvae from becoming queens.
“It’s really an awesome paper,” Amdam says, and it should inspire other honeybee researchers to see what they can learn in fruit flies. However, queen bee development is probably too complex to be explained by one ingredient in royal jelly, she says. “We just need to be careful in falling in love with a single explanation.”
In 2008, Ryszard Maleszka at Australian National University in Canberra, and his team showed that ‘epigenetic’ modifications that quiet genes are instrumental to the queen-making process. Honeybee larvae with reduced levels of a protein that silences genes by tagging them with chemicals become queens in the absence of royal jelly, they found.
“There are dozens of potentially important components in royal jelly and giving a special rank to one of them is misleading,” Maleszka says. If the entire social structure rested on a single protein, one mutation could collapse an entire colony.
Image 1: courtesy Wikimedia Commons. Image 2: Masaki Kamakura