Why does puberty cause us to stop growing?

All animals start as a single-celled organism and then begin to grow. At some point, of course, they will have to stop growing, but the process by which this happens is poorly understood.

New research by Alexander Shingleton of the University of Illinois at Chicago and colleagues identifies a potential trigger that stops fruit flies from growing, which has implications for understanding human development. The research is published in the Proceedings of the National Academy of Sciences.

In men, the body’s signal to stop growth occurs around puberty, although it still takes several years before growth actually stops. It is important to better understand this process, in part because of recent changes in the way children experience puberty.

“We know that the onset of puberty is getting younger and younger. But to understand why something changes, you have to understand how it works,” said Shingleton, a professor of biological sciences.

So the researchers looked at fruit flies, which undergo the equivalent of puberty when they metamorphose from larvae into adults. The theory of many biologists is that a larva stops growing when it reaches a certain body size, which triggers it in the process of becoming an adult. Other insects do this, such as the kissing bug, which uses a “stretch receptor” in its abdomen to monitor its size, Shingleton explained.

But Shingleton and his co-authors weren’t convinced that fruit flies used such a mechanism. They hypothesized that it had something to do with a steroid hormone involved in the growth of fruit flies, called ecdysone, which is similar to estrogen and testosterone in humans.

The researchers used a mathematical model to explore their idea. The model showed that body size is not the trigger that causes a fruit fly to stop growing. Instead, a “stop growth” switch is triggered by the gland that produces ecdysone. In the larval stage, this gland receives a lot of nutritional information that helps it decide how to regulate ecdysone production. But once ecdysone reaches a certain level, the gland no longer needs this nutritional information to make decisions and begins to self-regulate.

Researchers believe that no longer needing nutritional information is what triggers the fruit fly to stop growing. “It’s not that the fly is measured in a direct way,” Shingleton said.

He would like to see similar studies done in mammals, which could shed more light on the process of growth arrest in humans. But Shingleton suspects that fruit flies’ experience is related to ours, given that both involve similar steroid hormones and that fruit flies and humans transmit nutritional information via insulin.

Other researchers on the project are UIC undergraduate Amirali Monshizadeh, John Tyson of Virginia Tech and Stanislav Shvartsman of Princeton.