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Why Do We Freeze When Startled? New Study in Flies Points to Serotonin

Videos of flies (5x speed) using FlyWalker, a program that enables scientists to label and track the position of each of the fly’s footfalls, thereby building a high-resolution picture of it’s walking gait. Top: normal fly walking at around 25 mm/s. Bottom: fly with its VNC serotonin neurons stimulated, which slows its speed to 15 mm/s (Credit: Clare Howard/Mann lab/Columbia's Zuckerman Institute)

A Columbia University study in fruit flies has identified serotonin as a chemical that triggers the body’s startle response, the automatic deer-in-the-headlights reflex that freezes the body momentarily in response to a potential threat. Today’s study reveals that when a fly experiences an unexpected change to its surroundings, such as a sudden vibration, release of serotonin helps to literally — and temporarily — stop the fly in its tracks.

These findings, recently published in Current Biology , offer broad insight into the biology of the startle response, a ubiquitous, yet mysterious, phenomenon that has been observed in virtually every animal studied to date, from flies to fish to people.

“Imagine sitting in your living room with your family and — all of a sudden — the lights go out, or the ground begins to shake,” said Richard Mann , PhD, a principal investigator at Columbia’s Mortimer B. Zuckerman Mind Brain Behavior Institute and the paper’s senior author. “Your response, and that of your family, will be the same: You will stop, freeze and then move to safety. With this study, we show in flies that a rapid release of the chemical serotonin in their nervous system drives that initial freeze. And because serotonin also exists in people, these findings shed light on what may be going on when we get startled as well.”

In the brain, serotonin is most closely associated with regulating mood and emotion. But previous research on flies and vertebrates has shown it can also affect the speed of an animal’s movement. The Columbia researchers’ initial goal was to more fully understand how the chemical accomplished this.

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Biological ‘Rosetta Stone’ Brings Scientists Closer to Deciphering How the Body is Built

Time lapse of a developing drosophila embryo. (Credit: Carlos Sanchez-Higueras/Hombría lab/CABD)

Every animal, from an ant to a human, contains in their genome pieces of DNA called Hox genes. Architects of the body, these genes are keepers of the body’s blueprints; they dictate how embryos grow into adults, including where a developing animal puts its head, legs and other body parts. Scientists have long searched for ways to decipher how Hox genes create this body map; a key to decoding how we build our bodies.

Now an international group of researchers from Columbia University and the Spanish National Research Council (CSIC) based at the Universidad Pablo de Olavide in Seville, Spain have found one such key: a method that can systematically identify the role each Hox gene plays in a developing fruit fly. Their results, reported recently in Nature Communications , offer a new path forward for researchers hoping to make sense of a process that is equal parts chaotic and precise, and that is critical to understanding not only growth and development but also aging and disease.

“The genome, which contains thousands of genes and millions of letters of DNA, is the most complicated code ever written,” said study co-senior author Richard Mann , PhD, principal investigator at Columbia’s Mortimer B. Zuckerman Mind Brain Behavior Institute and a faculty member in the Department of Systems Biology . “Deciphering this code has proven so difficult because evolution wrote it in fits and starts over hundreds of millions of years. Today’s study offers a key to cracking that code, bringing us closer than ever to understanding how Hox genes build a healthy body, or how this process gets disrupted in disease.”

Read the full article at the Zuckerman Institute. 

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Building a Better Way to Decode the Genome

No Read Left Behind

Gradually eliminating low-affinity binding sites identified by NRLB (from left to right) results in a gradual reduction of gene expression (white); Credit: Mann Lab/Columbia’s Zuckerman Institute

As reported  by the Zuckerman Mind Brain Behavior Institute, Columbia University researchers have developed a new computational method for deciphering DNA’s most well-kept secrets, and this new algorithm may help find the links between genes and disease. 

The researchers included lead PI at Zuckerman  Richard Mann , PhD, with collaborator, Harmen Bussemaker , PhD, both faculty members of the Department of Systems Biology. They recently published their findings in the Proceedings of the National Academy of Sciences .

“The genomes of even simple organisms such as the fruit fly contain 120 million letters worth of DNA, much of which has yet to be decoded because the cues it provides have been too subtle for existing tools to pick up,” said Mann, who is also Higgins Professor of Biochemistry and Molecular Biophysics and senior author of the paper. “But our new algorithm lets us sweep through these millions of lines of genetic code and pick up even the faintest signals, resulting in a much more complete picture what DNA encodes.”

A few years ago, the two labs--Mann and Bussemaker--developed a genetic sequencing method called SELEX-seq to systematically characterize all Hox binding sites. Hox genes are known as the drivers of some of the body's earliest and most critical aspects of growth and differentiation. Still, SELEX-seq had limitations: It required the same DNA fragment to be sequenced over and over again. With each new round, more pieces of the puzzle were revealed, but information about those critical low-affinity binding sites remained hidden.

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Faculty

Barry Honig

Professor, Department of Systems Biology
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