A fruit fly larva normally begins metamorphosis -- the process of maturing into an adult -- by transforming into a pupa like one on the left. A University of Utah study found that a gene named DHR4 determines when this change begins. When scientists disabled the gene, fruit fly larvae began to mature prematurely and ended up as small pupae like the three on the right. The pupa at far right also is misshapen. Photo by Kirst King-Jones, University of Utah
When a fruit fly begins to mature from a juvenile larva into an adult, it is known as a pupa, like the one on the left. But when University of Utah researchers crippled a key gene that controls the timing and early stages of maturation, the pupa can fail to develop an adult head or legs, like the pupa on the right. Photo by Kirst King-Jones, University of Utah
When gene is disabled, young flies don’t grow up
University of Utah researchers showed that a fruit fly gene is crucial for determining when juveniles begin to mature into adults, and how the transformation initially proceeds. Understanding this process in humans may help explain how adorable children become surly teenagers.
When the DHR4 gene is disabled, fruit flies prematurely begin metamorphosis – maturation from an immature larva to a sexually active adult. It is the first genetic mutation found to cause early maturation in fruit flies, according to a new study in the Friday June 3 issue of the journal Cell. The flies are abnormally small and die as they enter adulthood, sometimes when their heads fail to emerge from their bodies.
"How does an animal know when it is ready to mature – what determines that time?" Thummel asks. "That’s a big question of which we have poor understanding. This gene, DHR4, controls the time at which the animal begins to mature. It also plays an important role – along with many other genes – during maturation."
How the Gene Works: Stop Eating and Grow Up!
"In insects, the larval period is exclusively devoted to growth," says Thummel. "Insects are pests because, in their larval form, they consume many times their body weight in food, which can include our crops. … When babies are born, they are 7 or 8 pounds. By the time they are entering puberty, they are about 80 pounds. That’s about a 10-fold increase in weight. Innocent childhood is a period essentially dedicated to growth, much like insects."
But while human teenagers often are voracious, fruit fly larvae wander away from food and stop eating when it’s time to mature into pupae.
The scientists concluded that the DHR4 gene controls the timing of metamorphosis and its initial stages by coordinating how hormones respond when a fruit fly larva has gained enough weight – and stored enough food – to begin the transformation to adulthood. When the gene was deactivated, larvae did not know whether or not they had gained enough weight, so they entered metamorphosis one day early and began adulthood as prepupae that were 40 percent lighter than normal and 60 percent to 90 percent of normal length.
Thummel concludes: "Our life cycle consists of embryonic development, growth, maturation, aging and then death. We have a good handle on how embryonic development and aging work at a molecular level. But the transition from growth to maturation is poorly understood. If we can study this further in insects using them as a model for humans, because they have so many components that also are present in humans, we can gain some insights into how these processes – the timing of maturation and maturation itself – work in all higher organisms, including people."
Lee Siegel | EurekAlert!
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