Fruit fly brain cells offer potential insight on human synapse formation

UCLA researchers discovered a pattern in fruit fly brain cells that might help explain how human brains make connections between their brain cells.

Orkun Akin, an assistant professor of neurobiology, and Bryce Bajar, a graduate student and first author on the paper, found developing fruit flies exhibited activity in their innermost eye cells before they were able to open their eyes.

This type of cell activity is fundamental to making connections in a developing brain in humans and other animals, said Lawrence Zipursky, a distinguished professor of biological chemistry and an author of the study. However, before this study, researchers thought this type of retinal activity only occurred in mammals, Akin said.

Researchers are still unsure what role this activity plays in the formation of neural connections, or synapses, during brain development because it is difficult to observe the neural activity of animals that develop within the uterus. However, this study will allow researchers to gain a clearer picture of brain cell development by observing species whose brain develops outside of a uterus.

Using technology Akin had previously developed to observe the development of live fruit fly brain cells, the researchers were able to study fruit fly brains while the flies were in the pupal stage of development, the stage during which a larva transitions to an adult.

Bajar said the researchers used GCaMP, a protein that lights up when there is activity in a cell, to detect this pattern of retinal activity.

The researchers then inserted GCaMP into different kinds of brain cells in the fly’s visual system. They observed the cells would light up together at the beginning of the pupal stage. However, several hours later, some of the cells would light up while others did not.

The researchers noticed the cells that exhibited the same activity pattern formed synapses in the adult brain, which could give them an idea about the role of innermost eye cells activity in adult synapse formation.

Akin said because they have the tools study this development in flies, they can begin to figure out which particular genes have a role in the formation of synapses.

The genes that control how the nervous system develops in a fly are the same genes that control neural development in the human brain, Zipursky said. By observing simpler organisms like flies, researchers can potentially discover how brain cells form connections in the human brain and the role these processes play in human brain development, he said.

“We may have a stepping stone to answering these questions and that turns out to be a fruit fly,” Akin said.