How mechanical tearing severs neuronal connections in the fruit fly

How mechanical tearing severs neuronal connections in the fruit fly

Researchers visualized the forces acting on dendrites during pruning by measuring their lengths (blue/red) and angles at dendritic junction points: A) before, B) after dendrite severing. Photo credit: WWU – Hull Lab

Scientists from the Institute of Neuro- and Behavioral Biology at the WWU have investigated the regulated breakdown of neuronal connections in the model system of the Drosophila fruit fly. They find that mechanical forces play an important role.

Nerve cells communicate with each other via long processes known as axons and dendrites, or more commonly, neurites. During development, these extensions initially grow and form connections with other cells, for example synapses with other nerve cells. Any neurites that are improperly linked or no longer needed are removed through a correction mechanism known as “pruning.” Such circumcision processes can appear drastic, and neurites sometimes appear to be severed directly from the nerve cell.

researchers around Dr. Sebastian Rumpf from the Institute of Neuro- and Behavioral Biology at the University of Münster have now found the mechanism of neurite transection. In a study published in the Journal of Cell Biologythe team shows that in sensory neurons of the fruit fly Drosophila melanogaster, pruning occurs through mechanical tearing.

In the fruit fly, large numbers of neurites are removed by pruning during the pupal phase or metamorphosis. “First, the neurites become very unstable. This is due to an intrinsic mechanism,” says Sebastian Rumpf. The main phase of pruning coincides with the phase when the animal changes its body shape, which is accompanied by strong body contractions.

“We have now found that these movements put so much strain on the fragile neurites that they are torn off,” explains Rumpf. The severed neurites are then recognized as “waste” and removed from the surrounding tissue.

Animal cells are constantly exposed to mechanical forces to which they can react, for example, by changing their shape. “Surprisingly little is known about the role of mechanical forces in the nervous system,” said lead authors Dr. Rafael Kramer and Dr. Neele Wolterhoff. “Our work now shows how mechanical pulling can affect nerve cells.”

The mechanism of circumcision was previously unclear and the role played by mechanical forces had not been studied. Instead, experts suspected that there must be a separation mechanism in the neurites themselves. However, the effects of potentially “separating” enzymes could always be better explained in different ways, so the mechanism remained unclear.

Detecting mechanical forces in Drosophila pupae is difficult because the animals cannot be removed from their pupal cases to make force measurements. To solve this problem, Kramer and Wolterhoff followed the circumcision process with live video microscopy and recorded many long videos of nerve cell trimming.

By analyzing these video recordings, they then demonstrated the existence of tensile forces. For example, the neurites were initially stretched before being torn off, indicating that they were under tension. Through genetic manipulations, they were also able to decrease the morphogenetic movements that led to errors in the circumcision process.

More information:
Rafael Kramer et al, Developmental Pruning of Sensory Neurites by Mechanical Tearing in Drosophila, Journal of Cell Biology (2023). DOI: 10.1083/jcb.202205004

Provided by the Westfälische Wilhelms-Universität Münster

Citation: How Mechanical Tearing Cuts Neural Connections in the Fruit Fly (2023, January 25), retrieved January 25, 2023 from

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